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crustacea

crustacea Sentence Examples

  • His order of wingless insects (Aptera) included Crustacea, spiders, centipedes and other creatures that now form classes of the Arthropoda distinct from the Hexapoda; it also included Hexapoda of parasitic and evidently degraded structure, that are now regarded as allied more or less closely to various winged insects.

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  • A near relationship between the Apterygota and the Crustacea has been ably advocated by H.

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  • Carpenter (1899, 1902-1904) has lately endeavoured to show an exact numerical correspondence in segmentation between the Hexapoda, the Crustacea, the Arachnida, and the most primitive of the Diplopoda.

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  • On either view it may be believed that the Hexapoda arose with the allied classes from a primitive arthropod stock, while the relationships of the class are with the Crustacea, the Chilopoda and the Diplopoda, rather than with the Arachnida.

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  • The science of insects began with Aristotle, who included in a class "Entoma" the true insects, the arachnids and the myriapods, the Crustacea forming another class ("Malacostraca") of the "Anaema" or "bloodless animals."

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  • Ray's "Insects" comprised the Arachnids, Crustacea, Myriapoda and Annelida, in addition to the Hexapods.

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  • Lime is, in fact, absorbed to an enormous extent by fishes, molluscs, crustacea, calcareous algae and sponges, starfishes, sea-urchins and feather stars, many polyzoa and a multitude of protozoa (mainly the foraminifera).

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  • Lamarck at the same time founded the class Crustacea for the lobsters, crabs and water-fleas, also until then included in the order Aptera of Linnaeus.

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  • The Arachnida form a distinct class or line of descent in the grade Euarthropoda, diverging (perhaps in common at the start with the Crustacea) from primitive Euarthropods, which gave rise also to the separate lines of descent known as the classes Diplopoda, Crustacea, Chilopoda and Hexapoda.

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  • The cerebral mass is in Limulus more easily separated by dissection as a median lobe distinct from the laterally placed ganglia of the cheliceral somite than is the case in Scorpio, but the relations are practically the same in the two forms. Formerly it was supposed that in Limulus both the chelicerae and the next following pair of appendages were prosthomerous, as in Crustacea, but the dissections of Alphonse Milne-Edwards (6) demonstrated VI FIG.

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  • Limulus thus agrees with Scorpio and differs from the Crustacea, in which there are three prosthomeres - one ocular and two carrying palpiform appendages.

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  • It is true that in the lower Crustacea (Apus, &c.) we have evidence of the gradual movement forward of the nerve-ganglia belonging to these FIG.

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  • But although in such lower Crustacea the nerve-ganglia of the third prosthomere have not fused with the anterior nerve-mass, there is no question as to the prae-oral position of two appendage-bearing somites in addition to the ocular prosthomere.

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  • The Crustacea have, in fact, three prosthomeres in the head and the Arachnida only two, and Limulus agrees with the Arachnida in this respect and differs from the Crustacea.

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  • Watase has shown, in a very convincing way, how by deepening the pit-like set of cells beneath a simple lens the more complex ommatidia of the compound eyes of Crustacea and Hexapoda may be derived from such a condition as that presented in the lateral eyes of Limulus and Scorpio.

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  • In the specialized ommatidia of the compound eyes of Crustacea and Hexapods the rhabdom is an important structure.'

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  • Possibly, however, an investigation of the development of the median eyes of some Crustacea(Apus,Palaemon)may prove them to be diplostichous in origin.

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  • The coxal glands of the Arachnida are structures of the same nature as the green glands of the higher Crustacea and the so-called " shell glands " of the Entomostraca.

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  • The coxal glands do not establish any special connexion between Limulus and Scorpio, since thay also occur in the same somite in the lower Crustacea, but it is to be noted that the coxal glands of Limulus are in minute structure and probably in function more like those of Arachnids than those of Crustacea.

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  • This body occurs also in the blood of Crustacea and of Molluscs, but its abundance in both Limulus and Scorpio is very marked, and gives to the freshly-shed blood a strong indigo-blue tint.

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  • the Myriapoda and some of the arthrostracous Crustacea.

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  • The only point in which the gut of Limulus resembles that of Scorpio rather than that of any of the Crustacea, is in possessing more than a single pair of ducts or lateral outgrowths connected with ramified gastric glands or gastric caeca.

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  • The Crustacea never have more than one pair.

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  • This is a very definite and remarkable agreement, since such a reticular gonocoel is not found in Crustacea (except in the male Apus).

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  • The Crustacea are - with the exception of the Cirrhipedia - remarkable for having stiff, motionless spermatozoids.

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  • Limulus agrees with the majority of the Crustacea in being destitute of renal excretory caeca or tubes opening into the hinder part of the gut.

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  • (From Lankester, "Limulus an Arachnid.) of adaptation to the changed physiological conditions of respiration, and not of morphological significance, since a pair of renal excretory tubes of this nature is found in certain Amphipod Crustacea (Talorchestia, &c.) which have abandoned a purely aquatic life.

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  • They have appeared independently in connexion with a change in the excretion of nitrogenous waste in Arachnids, Crustacea, and the other classes of Arthropoda when aerial, as opposed to aquatic, respiration has been established - and they have been formed in some cases from the mesenteron, in other cases from the proctodaeum.

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  • The great Arthropod class, the Crustacea, presents to the zoologist at the present day an immense range of forms,.

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  • They differ from the Crustacea in that they have only a single pair of prae-oral appendages, the second pair being definitely developed as mandibles.

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  • This fact renders their association with the Crustacea impossible, if classification is to be the expression of genetic affinity inferred from structural coincidence.

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  • Little is known of the form of the appendages in the lowest archaic Arachnida, but the tendency of those of the prosomatic somites has been (as in the Crustacea) to pass from a generalized bi-ramose or multi-ramose form to, that of uni-ramose antennae, chelae and walking legs.

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  • - Extinct archaic Arachnida, in which (as in the Entomostracous Crustacea) the number of well-developed somites may be more or less than eighteen and may be grouped only as head (prosoma) and trunk or may be further differentiated.

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  • The members of this group, whilst resembling the lower Crustacea (as all lower groups of a branching genealogical tree must do), differ from them essentially in that the head exhibits only one prosthomere (in addition to the eye-bearing prosthomere) with palpiform appendages (as in all Arachnida) instead of two.

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  • The Pantopoda stand in the same relation to Limulus and Scorpio that Cyamus holds to the thoracostracous Crustacea.

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  • Crustacea are abundant.

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  • MaXaKOVTpaKa, soft-shelled Anaema (= Crustacea).

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  • "Evropa, insected Anaema or Insects (= Arthropoda, exclusive of Crustacea).

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  • Crustacea.

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  • Classes: Arachnida, Insecta (including Sub-Classes M y riapoda, Hexapoda), Crustacea (including Sub-Classes Entomostraca, Malacostraca), Epizoa (Epizootic Crustacea), Annellata (Chaeto p ods and Leeches), Cirripedia.

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  • He upset (1830) Cuvier's retention of the Cirripedes among Mollusca, and his subsequent treatment of them as an isolated class, by showing that they begin life as free-swimming Crustacea identical with the young forms of other Crustacea.

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  • Classes: Crustacea, Arachnida,Myriapoda,Insecta,Chaetognatha, Annelida.

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  • Fritz Muller, by his studies on Crustacea (Fiir Darwin, 1864), showed the way in which genealogical theory may be applied to the minute study of a limited group.

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  • Dana on Zoophytes (1846), Geology (1849) and Crustacea (2 vols., 1852-1854).

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  • Udonella occurs on parasitic Crustacea).

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  • In Japan, as elsewhere, the principal crustacea are found in the sea.

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  • Malta has several species of zoophytes, sponges, mollusca and crustacea.

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  • Crustacea >>

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  • Pure calcareous sand and calcareous mud are formed by wave action on the shores of coral islands where the only material available is coral and the accompanying calcareous algae, crustacea, molluscs and other organisms secreting carbonate of lime.

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  • The larger shrimp-like crustacea are generally known as "prawns," the name being especially applied in Britain to the species Leander serratus, formerly called Palaemon serratus, which is highly esteemed for the table.

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  • Under the heading Crustacea the Entomostraca have already been distinguished not only from the Thyrostraca or Cirripedes, but also from the Malacostraca, and an intermediate group of which the true position is still disputed.

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  • Medusae capture their prey, consisting of small organisms of various kinds, especially Crustacea, by means of the tentacles which hang out like fishing-lines in all directions.

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  • The mouth opens through a narrow pharynx (p) into a chamber which is (as in Crustacea) at once crop and gizzard, the mastax (ma), whose thickenings are imbedded in the posteroventral wall.

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  • are twice as long as the 3to 5-toothed Thus the crop-gizzard unci; c, virgate - mallei rod-like, manubria has the same comand fulcrum very long, unci Ior 2-toothed; bination of structures d forcipate - rami large and used as a foras we find in the ceps, mallei rod-like, unci pointed or evanstomach of higher escent; e, incudate - stout fulcrum, rami Crustacea, with which formingaforceps, mallei evanescent; f, unwe may call it homocinate - unci large, 2-toothed, manubria plastic. The trophi evanescent, incus slender; g, ramate - rami are (I) a median incus subquadrantic, fulcrum rudimentary, manY - shaped, with the ubria evanescent; h,malleo-ramate - mallei (fulcrum) distal fastened by their unci to the rami, manubria foot and the arms (rami) looped, rami large and fulcrum slender.

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  • The Rotifera are all aquatic, the majority dwelling in fresh water with Protozoa and Protophyta, as well as Entomostracous Crustacea.

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  • TRILOBITES, extinct Arthropoda, formerly classified with the Crustacea, but of late years relegated to the Arachnida, which occurred abundantly in seas of the Cambrian and Silurian periods, but disappeared entirely at the close of the Palaeozoic epoch.

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  • ,Among the known fossils are vermes, crustacea and probably brachiopods and pteropods The character of the sediments of the Proterozoic is such as to show that mature weathering affected the older rocks before their material was worked over into the Proterozoic formations.

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  • Certain other remarkable crustacea, however, had made their appearance, especially in connection with the Salina series of the east.

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  • The life of the land waters was also noteworthy, especially for the great deployment of what may be called the crustacean-ostracodermo-vertebrate group. The crustacea were represented by eurypterids, the ostracoderms by numerous strange, vertebrate-like forms (Cephalaspis, Gyathaspis, Trematopsis, Bothriolepss, &c.), and the vertebrates by a great variety of fishes, The land life of the period is represented more fully among the fossils than that of any preceding period.

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  • Their affinities with the lower Crustacea were recognized by Cuvier and his contemporaries, but it was one of the brilliant discoveries of that remarkable and too-little-honoured naturalist, J.

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  • Vaughan Thompson, of Cork, which decided their position as Crustacea.

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  • Thus the condition in the Dermaptera is more primitive than in any other Pterygote order except the Ephemeroptera (Mayflies) which are still more generalized, the primitive mesodermal ducts (oviducts and vasa deferentia) opening by paired apertures as in the Crustacea.

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  • Albinism is restricted to no particular class of the animal kingdom; for partial albinism at least is known to occur in Coelentera, worms, Crustacea, Myriapoda, Coleoptera,Arachnida and fishes.

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  • The inhabitants of the waters of this geographical phase include mollusca, which are supposed to have lived in brackish or fresh water, such as Anthracomya, Naiadites, Carbonicola, and many forms of Crustacea, e.g.

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  • This estuary they called the Rio dos Camaroes (the river of Prawns), from the 2 abundance of the crustacea found therein.

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  • Crustacea occupied an extremely prominent place; there were Phyllocarids such as Hymenocaris, and Ostracods like Entomidella; but by far the most important in numbers and development were the Trilo bites, now extinct, but in palaeozoic times so abundant.

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  • Under this zoological title are included several groups of Crustacea, united by characters which attest their common origin, though some, and probably all of them, were already separated in distant geological ages, and some have now attained a peculiar isolation.

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  • New light, however, has been thrown upon the "intellectual" capacity of Crustacea by the proof that the spider-crabs deliberately use changes of raiment to harmonize with their surroundings, donning and doffing various natural objects as we do our manufactured clothes.

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  • A bibliography of the order is given in that author's Crustacea of Norway, vol.

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  • It adapts itself to parasitic life not only in fishes, but in its own class Crustacea, and that in species of every order, its own included.

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  • The order has been divided into seven tribes, of which a fuller summary than can here be given will be found in Stebbing, History of Crustacea (1893).

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  • APTERA (Greek for "wingless"), a term in zoological classification applied by Linnaeus to various groups of wingless arthropods, including some of the insects, the centipedes, the millipedes, the Arachnida (scorpions, spiders, &c.) and the Crustacea.

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  • i, Mn.; 4), with toothed apex and sub-apical grinding surface, like those of certain Crustacea; by the presence between the mandibles and maxillae of a pair of appendages (superlinguae or maxil ' x lulae), fig.

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  • They are distributed thus: Vertebrata, 8 species; Insecta, 17; Arachnida, 12; Myriapoda, 2; Crustacea, 5; Vermes, 3; Mollusca, 1.

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  • CRUSTACEA, a very large division of the animal kingdom, comprising the familiar crabs, lobsters, crayfish, shrimps and prawns, the sandhoppers and woodlice, the strangely modified barnacles and the minute water-fleas.

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  • In point of size also the Crustacea vary within very wide limits.

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  • The habits of the Crustacea are no less diversified than their structure.

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  • Apart from the numerous parasitic forms, the only Crustacea which have adopted a strictly sedentary habit of life are the Cirripedia, and here, as elsewhere, profound modifications of structure have resulted, leading ultimately to a partial assumption of the radial type of symmetry which is so often associated with a sedentary life.

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  • Perhaps the most complete degeneration is found in the Rhizocephala, which are parasitic on other Crustacea.

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  • Many of the larger species of Crustacea are used as food by man, the most valuable being the lobster, which is caught in large quantities on both sides of the North Altantic. Perhaps the most important of all Crustacea, however, with respect to the part which they play in the economy of nature, are the minute pelagic Copepoda, of which incalculable myriads form an important constituent of the " plankton " in all the seas of the globe.

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  • The application of the morphological method to the Crustacea may perhaps be dated from the work of J.

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  • Vaughan Thompson demonstrated the existence of metamorphosis in the development of the higher Crustacea.

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  • It is noteworthy that even at this late date the Cirripedia (Thyrostraca) were still excluded from the Crustacea, though Darwin's Monograph (1851-1854) was soon to make them known with a wealth of anatomical and systematic detail such as was available, at that time, for few other groups of Crustacea.

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  • In more recent years the long and constantly increasing list of writers on Crustacea contains no name more honoured than that of the veteran G.

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  • It is quite probable, however, that in the primitive ancestors of existing Crustacea a still smaller number of somites formed the head.

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  • A character which recurs in the most diverse groups of the Crustacea, and which is probably to be regarded as a primitive attribute FIG.

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  • - Amid the great variety of forms assumed by the appendages of the Crustacea, it is possible to trace, more or less plainly, the modifications of a fundamental type consisting of a peduncle, the protopodite, bearing two branches, the endopodite and exopodite.

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  • The Phyllopoda are the only Crustacea in which distinct and functional gnathobasic processes are found on appendages far removed from the mouth.

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  • The two distal endites are regarded as corresponding to the endopodite and exopodite of the higher Crustacea, the axis or corm of the Phyllopod limb representing the protopodite.

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  • It is not altogether easy to recognize the homologies of the endites and exites even within the order Phyllopoda, and the identification of the two distal endites as corresponding to the endopodite and exopodite of higher Crustacea is not free from difficulty.

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  • In many Crustacea the eyes are borne on stalks which are movably articulated with the head and which may be divided into two or three segments.

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  • In the great majority of Crustacea the antennules are purely sensory in function and carry numerous " olfactory " hairs.

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  • The antennae (second antennae) are of special interest on account of the clear evidence that, although preoral in position in all adult Crustacea, they were originally postoral appendages.

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  • In almost all Crustacea the food-canal runs straight through the body, except at its anterior end, where it curves downwards to the ventrally-placed mouth.

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  • As in the other Arthropoda, the circulatory system in Crustacea is largely 1 6/ lacunar, the blood flowing in spaces or channels without definite walls.

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  • The most important excretory or renal organs of the Crustacea are two pairs of glands lying at the base of the antennae and of the second maxillae respectively.

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  • In addition to these two pairs of glands, which are in all probability the survivors of a series of segmentally arranged coelomoducts present in the primitive Arthropoda, other excretory organs have been described in various Crustacea.

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  • The eyes of Crustacea are of two kinds, the unpaired, median or "nauplius " eye, and the paired compound eyes.

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  • Mention should also be made of the partial or complete atrophy of the eyes in many Crustacea which live in darkness, either in the deep sea or in subterranean habitats.

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  • Recent observations, however, make it very doubtful whether aquatic Crustacea can hear at all, in the proper sense of the term, and it has been shown that one function, at least, of the so-called otocysts is connected with the equilibration of the body.

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  • In nearly all Crustacea the antennules and often also the antennae bear groups of hair-like filaments in which the chitinous cuticle is extremely delicate and which do not taper to a point but end bluntly.

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  • In addition to the digestive and excretory glands already mentioned, various glandular structures occur in the different groups of Crustacea.

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  • - Many Crustacea belonging to very different groups (Ostracoda, Copepoda, Schizopoda, Decapoda) possess the power of emitting light.

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  • In the great majority of Crustacea the sexes are separate.

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  • Very few Crustacea are viviparous in the sense that the eggs are retained within the body until hatching takes place (some Phyllopoda), but, on the other hand, the great majority carry the eggs in some way or other after their extrusion.

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  • The majority of the Crustacea are hatched from the egg in a form differing more or less from that of the adult, and pass through a series of free-swimming larval stages.

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  • They are of interest, however, rather from the point of view of general embryology than from that of the special student of the Crustacea, and cannot be fully dealt with here.

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  • The larval metamorphoses of the Crustacea have attracted much attention, and have been the subject of much discussion in view of their bearing on the phyiogenetic history of the group. In those Crustacea in which the series of larval stages is most complete, the starting-point is the form already mentioned under the name of nauplius.

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  • In most Crustacea, however, this primitive scheme is more or less modified.

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  • Although fossil remains of Crustacea are abundant, from the most ancient fossiliferous rocks down to the most recent, their study has hitherto contributed little to a precise knowledge of the phylogenetic history of the class.

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  • In the dearth of trustworthy evidence as to the actual forerunners of existing Crustacea, we are compelled to rely wholly FIG.

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  • The first attempts to reconstruct the genealogical history of the Crustacea started from the assumption that the " theory of recapitulation " could be applied to their larval history.

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  • As regards the nauplius, however, the constancy of its general character in the most widely diverse groups of Crustacea strongly suggests that it is a very ancient type, and the view has been advocated that the Crustacea must have arisen from an unsegmented nauplius-like ancestor.

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  • The resemblances between the Crustacea and the Annelid worms, in such characters as the structure of the nervous system and the mode of growth of the somites, can hardly be ignored.

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  • 5, 3, Eryon arctiformis, Schl.; Lithographic stone, Solen6, stock of the Crustacea, such as the paired eyes and the shell-fold, are not present in the nauplius.

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  • In those Copepods in which the palps of the mandibles as well as the antennae are biramous and natatory, the first three pairs of appendages retain throughout life, with little modification, the shape and function which they have in the nauplius stage, and must, in all likelihood, be regarded as approximating to those of the primitive Crustacea.

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  • The probable course of evolution of the different groups of Crustacea from this hypothetical ancestral form can only be touched on here.

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  • The modern classification of Crustacea may be said to have been founded by P. A.

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  • Class Crustacea.

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  • Crustacea and fish abound on the reefs.

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  • BARNACLE, a name applied to Crustacea of the division Cirripedia or Thyrostraca.

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  • His earlier publications were on zoology; he dealt with the Amphibia (1839), Reptiles (1840), with Mollusca and Crustacea (1845) and more generally with the invertebrate fauna of the Mediterranean (1854).

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  • The names Condylopoda and Gnathopoda have been subsequently proposed for the same group. The word refers to the jointing of the chitinized exo-skeleton of the limbs or lateral appendages of the animals included, which are, roughly speaking, the Crustacea, Arachnida, Hexapoda (so-called " true insects "), Centipedes and Millipedes.

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  • Lamarck's penetrating genius is chiefly responsible for the shrinkage of the word Insecta, since it was he who, forty years after Linnaeus's death, set up and named the two great classes Crustacea and Arachnida (included by Linnaeus under Insecta as the order " Aptera "), assigning to them equal rank with the remaining Insecta of Linnaeus, for which he proposed the very appropriate class-name " Hexapoda."

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  • Lamarck, however, appears not to have insisted on this name Hexapoda, and so the class of Pterygote Hexapods came to retain the group-name Insecta, which is, historically or etymologically, no more appropriate to them than it is to the classes Crustacea and Arachnida.

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  • 8) of the marine branchiate worms are the same things genetically as the " legs " of Crustacea and Insects (figs.

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  • Lankester (2) was the first to suggest that (as is actually the fact in the Nauplius larva of the Crustacea) the prae-oral somites or prosthomeres and their appendages were ancestrally postoral, but have become prae-oral " by adaptational shifting of the oral aperture."

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  • (After Goodrich.) The Crustacea (fig.

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  • The three prosthomeres or prae-oral somites of Crustacea due to the sinking back of the mouth one somite farther than in Arachnida are not clearly indicated by coelomic cavities in the embryo, but their existence is clearly established by the development and position of the appendages and by the neuromeres.

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  • The eyes in some Crustacea are mounted on articulated stalks, and from the fact that they can after injury be replaced by antennalike appendages it is inferred that they represent the parapodia of the most anterior prosthomere.

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  • The Crustacea are tetartognathous.

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  • As in Crustacea and Arachnida, FIG.

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  • The existence of this third prosthomere corresponding to the third prosthomere of the Crustacea is a strong argument for the derivation of the Hexapoda, and with them the Chilopoda, from some offshoot of the Crustacean stem or class.

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  • The buccal somite, with its mandibles, is in Hexapoda, as in Crustacea, the fourth: they are tetartognathous.

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  • In Crustacea the fourth or mandibular somite never has less than the two following somites associated with it by the adaptation of their appendages as jaws, and the ankylosis of their terga with that of the prosthomeres.

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  • But in higher Crustacea the cephalic " tagma " is extended, and more somites are added to the fusion, and their appendages adapted as jaws of a kind.

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  • 7) - thus six in all (as in some Crustacea), including prosthomeres, all ankylosed by their terga to form a cephalic shield.

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  • Lankester (5) has shown (and his views have been accepted by Professors Korschelt and Heider in their treatise on Embryology) that the limb of the lowest Crustacea, such as Apus, consists of a corm or axis which may be jointed, and gives rise to outgrowths, either leaf-like or filiform, on its inner and outer margins (endites and exites).

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  • It is not true that all the biting processes of the Arthropod limb are thus produced - for instance, the jaws of Peripatus are formed by the axis or corm itself, whilst the poisonjaws of Chilopods, as also their maxillae, appear to be formed rather by the apex or terminal region of the ramus of the limb; but the opposing jaws (= hemignaths) of Crustacea, Arachnida and Hexapoda are gnathobases, and not the axis or corm.

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  • to) becomes in Crustacea the " walking leg " of the mid-region of the body; it becomes the palp or jointed process of anterior segments.

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  • Such chelate rami or limbbranchesare independently developed in Crustacea and inArachnida, and are carried by somites of the body which do not correspond in position in the two groups.

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  • A, A walking leg; p ' to p 4, Since the eye-stalks of Podophthalthe characteristic " pads "; f, mate Crustacea represent appendthe foot; cl', c1 2, the two ages, we are forced to the conclusion claws.

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  • that the sessile eyes of other B, An oral papilla, one of Crustacea, and of other Arthropoda the second pair of post-oral generally, indicate the position of appendages.

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  • Milne-Edwards, who was followed by Huxley, long ago formulated the conclusion that the eye-stalks of Crustacea are modified appendages, basing his argument on a specimen of Palinurus (figured in Bateson's book (1), in which the eye-stalk of one side is replaced by an antenniform palp. Hofer (6) in 1894 described a similar case in Astacus.

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  • (4) Three of the rami of the primitive limb (endites 5 and 6, and exite I) specially developed as endopodite, exopodite, and epipodite - the first two often as firm and strongly chitinized, segmented, leg-like structures; the original axis or corm reduced to a basal piece, with or without a distinct gnathobase (endite i)- typical tri-ramose limb of higher Crustacea.

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  • This may be filiform or brush-like or lamellate when it is an antenna or palp; a simple spike (walking leg of Crustacea, of other aquatic forms, and of Chilopods and Diplopods); the terminal joint flattened (swimming leg of Crustacea and Gigantostraca); the terminal joint provided with two or with three recurved claws (walking leg of many terrestrial forms - e.g.

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  • En s, The rudimentary sixth endite (exopodite of higher Crustacea).

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  • This is the typical " bi-ramose limb " often found in Crustacea.

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  • The rami may be flattened for swimming, when it is " a bi-ramose swimmeret," or both or only one may be filiform and finely annulate; this is the form often presented by the antennae of Crustacea, and rarely by prae-oral appendages in other Arthropods.

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  • The endopodite may be retained as a small segmented palp at the side of the gnathobase or disappear (mandible of Crustacea, Chilopoda and Hexapods).

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  • Its jointing (segmentation) may be retained, but its rami disappear (Podophthalmous Crustacea).

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  • Crustacea).

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  • (io) The forms assumed by special modification of the elements of the parapodium in the maxillae, labium, &c., of Hexapods, Chilopods, Diplopods, and of various Crustacea, deserve special enumeration, but cannot be dealt with without ample space and illustration.

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  • It seems probable that there are branchial plumes or filaments in some Arthropoda (some Crustacea) which can be identified with the distinct branchial organs of Chaetopoda, which lie dorsal of the parapodia and are not part of the parapodium.

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  • In Crustacea and Hexapoda of all grades we find compound eyes with the more complicated ommatidia described above.

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  • But they seem to point to a community of origin of Hexapods and Crustacea in regard to the complicated ommatidia of the compound eye, and to a certain isolation of the Arachnida, which are, however, traceable, so far as the eyes are concerned, to a distant common origin with Crustacea and Hexapoda through the very simple compound eyes (monostichous, polymeniscous) of Limulus.

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  • The Malpighian tubes of Hexapods are outgrowths of the proctodaeum, but those of Scorpion and the Amphipod Crustacea are part of the metenteron or endodermal gut, though originating near its junction with the proctodaeum.

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  • The absence of such renal caeca in Limulus and their presence in the terrestrial Arachnida is precisely on a parallel with their absence in aquatic Crustacea and their presence in the feebly branchiate Amphipoda.

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  • (Compare the definition of the class Chilopoda.) The movement of the legs in Diplopoda is like that of those of Peripatus, of the Phyllopod Crustacea, and of the parapodia of Chaetopoda, symmetrical and identical on the two sides of the body.

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  • - CRusTAcEA.

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  • No tracheate Crustacea are known, but some terrestrial Isopoda develop pulmonary in-sinkings of the integument.

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  • The lateral eyes of Crustacea are polymeniscous, with highly specialized retinulae like those of Hexapoda, and unlike the simpler compound lateral eyes of lower Arachnida.

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  • The Crustacea exhibit a longer and more complete series of forms than any other class of Arthropoda, and may be regarded as preserving the most completely represented line of descent.

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  • The first prosthomere has its appendages represented by the compound eyes and a protocerebrum, the second has the antennae for its appendages and a deutocerebral neuromere, the third has suffered suppression of its appendages (which corresponded to the second pair of antennae of Crustacea), but has a tritocerebrum and coelomic chamber.

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  • The number is significant, since it agrees with that found in Edriophthalmous Crustacea, and assigns the labium of the Hexapod to the same somite numerically as that which carries the labium-like maxillipedes of those Crustacea.

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  • It appears from observation of the embryo that whilst the first prosthomere of Centipedes has its appendages reduced and represented only by eye-patches (as in Arachnida, Crustacea and Hexapoda), the second has a rudimentary antenna, which disappears, whilst the third carries the permanent antennae, which accordingly correspond to the second antennae of Crustacea, and are absent in Hexapoda.

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  • twenty-one somites in all (as in the higher Crustacea).

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  • The Hexapoda are not only all confined to a very definite disposition of the somites, appendages and apertures, as thus indicated, but in other characters also they present the specialization of a narrowly-limited highly-developed order of such a class as the Crustacea rather than a range from lower more generalized to higher more specialized forms such as that group and also the Arachnida present.

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  • The lateral eyes of Hexapoda, like those of Crustacea, belong to the most specialized type of " compound eye," found only in these two classes.

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  • Our general conclusion from a survey of the Arthropoda amounts to this, that whilst Peripatus, the Diplopoda, and the Arachnida represent terrestrial offshoots from successive lower grades of primitive aquatic Arthropoda which are extinct, the Crustacea alone present a fairly full series of representatives leading upwards from unspecialized forms. The latter were not very far removed from the aquatic ancestors (Trilobites) of the Arachnida, but differed essentially from them by the higher specialization of the head.

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  • On the other hand, the facts that the Hexapoda and the Chilopoda have triprosthomerous heads, that the Hexapoda have the same total number of somites as the nomomeristic Crustacea, and the same number of opisthomeres in the head as the more terrestrial Crustacea, together with the same adaptation of the form of important appendages in corresponding somites, and that the compound eyes of both Crustacea and Hexapoda are extremely specialized and elaborate in structure and identical in that structure, all lead to the suggestion that the Hexapoda, and with them, at no distant point, the Chilopoda, have branched off from the Crustacean main stem as specialized terrestrial lines of descent.

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  • And it seems probable that in the case of the Hexapoda, at any rate, the point of departure was subsequent to the attainment of the nomomeristic character presented by the higher grade of Crustacea.

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  • It ranges from Iceland to the shores of the Red Sea, and lives chiefly on marine worms, crustacea and such molluscs as it is able to obtain.

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  • The manioc root is also largely consumed, together with several other roots and vegetables; but little animal foods (save fish and freshwater Crustacea) is taken by the mass of the people except at festival times.

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  • THYROSTRACA, an order of Crustacea, comprising barnacles, acorn shells and some allied degenerate parasites.

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  • In strong contrast with the condition in most Crustacea, the spermatozoa are mobile.

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  • Studer (Crustacea of the Gazelle, 1882) records Balanus amphitrite (Darwin?) from roots and stems of mangroves in the Congo, where, he says, " it follows the mangroves as far as their vegetation extends along the stream, to six sea-miles from the mouth."

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  • The compactness of the class Crustacea is generally admitted; of the precise affinities of its subdivisions there is still much to learn.

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  • The aquarium of the zoological station at Naples contains the finest collection in the world of marine animals, showing the wonderful variety of the different species of fish, molluscs, crustacea, &c., found in the Mediterranean.(E.

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  • Most conspicuous among the appendages of the head are the feelers or antennae, which correspond to the anterior feelers A (antennules) of Crustacea.

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  • His order of wingless insects (Aptera) included Crustacea, spiders, centipedes and other creatures that now form classes of the Arthropoda distinct from the Hexapoda; it also included Hexapoda of parasitic and evidently degraded structure, that are now regarded as allied more or less closely to various winged insects.

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  • A near relationship between the Apterygota and the Crustacea has been ably advocated by H.

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  • Carpenter (1899, 1902-1904) has lately endeavoured to show an exact numerical correspondence in segmentation between the Hexapoda, the Crustacea, the Arachnida, and the most primitive of the Diplopoda.

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  • On either view it may be believed that the Hexapoda arose with the allied classes from a primitive arthropod stock, while the relationships of the class are with the Crustacea, the Chilopoda and the Diplopoda, rather than with the Arachnida.

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  • The science of insects began with Aristotle, who included in a class "Entoma" the true insects, the arachnids and the myriapods, the Crustacea forming another class ("Malacostraca") of the "Anaema" or "bloodless animals."

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  • Ray's "Insects" comprised the Arachnids, Crustacea, Myriapoda and Annelida, in addition to the Hexapods.

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  • These three authors definitely separated the Arachnida, Crustacea and Myriapoda as classes distinct from the Insecta (see Hexapoda).

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  • The plankton is divided into (a) the Zoo-plankton (such as the minute crustacea and the eggs and larva of fishes and many other marine animals); and (b) the Phyto-plankton, that is, the minute algae, diatoms, peridinians, some flagellate protozoa, spores of alga, etc. The investigation of the plankton from a new point of view, begun by Hansen in 1889, was continued by Lohmann at Kiel, by Cleve in Sweden, by Gran and Ostenfeldt in Norway and Denmark, and by Herdman, Allen and others in England.

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  • Lime is, in fact, absorbed to an enormous extent by fishes, molluscs, crustacea, calcareous algae and sponges, starfishes, sea-urchins and feather stars, many polyzoa and a multitude of protozoa (mainly the foraminifera).

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  • Lamarck at the same time founded the class Crustacea for the lobsters, crabs and water-fleas, also until then included in the order Aptera of Linnaeus.

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  • The Arachnida form a distinct class or line of descent in the grade Euarthropoda, diverging (perhaps in common at the start with the Crustacea) from primitive Euarthropods, which gave rise also to the separate lines of descent known as the classes Diplopoda, Crustacea, Chilopoda and Hexapoda.

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  • The cerebral mass is in Limulus more easily separated by dissection as a median lobe distinct from the laterally placed ganglia of the cheliceral somite than is the case in Scorpio, but the relations are practically the same in the two forms. Formerly it was supposed that in Limulus both the chelicerae and the next following pair of appendages were prosthomerous, as in Crustacea, but the dissections of Alphonse Milne-Edwards (6) demonstrated VI FIG.

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  • Limulus thus agrees with Scorpio and differs from the Crustacea, in which there are three prosthomeres - one ocular and two carrying palpiform appendages.

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  • It is true that in the lower Crustacea (Apus, &c.) we have evidence of the gradual movement forward of the nerve-ganglia belonging to these FIG.

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  • But although in such lower Crustacea the nerve-ganglia of the third prosthomere have not fused with the anterior nerve-mass, there is no question as to the prae-oral position of two appendage-bearing somites in addition to the ocular prosthomere.

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  • The Crustacea have, in fact, three prosthomeres in the head and the Arachnida only two, and Limulus agrees with the Arachnida in this respect and differs from the Crustacea.

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  • Watase has shown, in a very convincing way, how by deepening the pit-like set of cells beneath a simple lens the more complex ommatidia of the compound eyes of Crustacea and Hexapoda may be derived from such a condition as that presented in the lateral eyes of Limulus and Scorpio.

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  • In the specialized ommatidia of the compound eyes of Crustacea and Hexapods the rhabdom is an important structure.'

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  • Possibly, however, an investigation of the development of the median eyes of some Crustacea(Apus,Palaemon)may prove them to be diplostichous in origin.

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  • The coxal glands of the Arachnida are structures of the same nature as the green glands of the higher Crustacea and the so-called " shell glands " of the Entomostraca.

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  • The coxal glands do not establish any special connexion between Limulus and Scorpio, since thay also occur in the same somite in the lower Crustacea, but it is to be noted that the coxal glands of Limulus are in minute structure and probably in function more like those of Arachnids than those of Crustacea.

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  • This body occurs also in the blood of Crustacea and of Molluscs, but its abundance in both Limulus and Scorpio is very marked, and gives to the freshly-shed blood a strong indigo-blue tint.

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  • the Myriapoda and some of the arthrostracous Crustacea.

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  • The only point in which the gut of Limulus resembles that of Scorpio rather than that of any of the Crustacea, is in possessing more than a single pair of ducts or lateral outgrowths connected with ramified gastric glands or gastric caeca.

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  • The Crustacea never have more than one pair.

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  • This is a very definite and remarkable agreement, since such a reticular gonocoel is not found in Crustacea (except in the male Apus).

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  • The Crustacea are - with the exception of the Cirrhipedia - remarkable for having stiff, motionless spermatozoids.

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  • Limulus agrees with the majority of the Crustacea in being destitute of renal excretory caeca or tubes opening into the hinder part of the gut.

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  • (From Lankester, "Limulus an Arachnid.) of adaptation to the changed physiological conditions of respiration, and not of morphological significance, since a pair of renal excretory tubes of this nature is found in certain Amphipod Crustacea (Talorchestia, &c.) which have abandoned a purely aquatic life.

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  • They have appeared independently in connexion with a change in the excretion of nitrogenous waste in Arachnids, Crustacea, and the other classes of Arthropoda when aerial, as opposed to aquatic, respiration has been established - and they have been formed in some cases from the mesenteron, in other cases from the proctodaeum.

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  • The great Arthropod class, the Crustacea, presents to the zoologist at the present day an immense range of forms,.

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  • When it is admitted - as seems to be reasonable - that the primitive Arachnida would, like the primitive Crustacea, be anomomeristic and anomotagmic, we shall not demand of claimants for the rank of primitive Arachnids agreement with Limulus and Scorpio in respect of the exact number of their somites and the exact grouping of those somites; and when we see how diverse are the modifications of the branches of the appendages both in Arachnida and in other classes of Arthropoda, we shall not over-estimate a difference in the form of this or that appendage exhibited by the claimant as compared with the higher Arachnids.

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  • They differ from the Crustacea in that they have only a single pair of prae-oral appendages, the second pair being definitely developed as mandibles.

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  • This fact renders their association with the Crustacea impossible, if classification is to be the expression of genetic affinity inferred from structural coincidence.

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  • They are strangely modified and degenerate, but seem to be (as explained in the systematic review) the remnant of an Arachnidan group holding the same relation to the scorpions which the Laemodipoda hold to the Podophthalmate Crustacea.

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  • Little is known of the form of the appendages in the lowest archaic Arachnida, but the tendency of those of the prosomatic somites has been (as in the Crustacea) to pass from a generalized bi-ramose or multi-ramose form to, that of uni-ramose antennae, chelae and walking legs.

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  • - Extinct archaic Arachnida, in which (as in the Entomostracous Crustacea) the number of well-developed somites may be more or less than eighteen and may be grouped only as head (prosoma) and trunk or may be further differentiated.

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  • The members of this group, whilst resembling the lower Crustacea (as all lower groups of a branching genealogical tree must do), differ from them essentially in that the head exhibits only one prosthomere (in addition to the eye-bearing prosthomere) with palpiform appendages (as in all Arachnida) instead of two.

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  • The Pantopoda stand in the same relation to Limulus and Scorpio that Cyamus holds to the thoracostracous Crustacea.

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  • Crustacea are abundant.

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  • MaXaKOVTpaKa, soft-shelled Anaema (= Crustacea).

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  • "Evropa, insected Anaema or Insects (= Arthropoda, exclusive of Crustacea).

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  • Classes: Arachnida, Insecta (including Sub-Classes M y riapoda, Hexapoda), Crustacea (including Sub-Classes Entomostraca, Malacostraca), Epizoa (Epizootic Crustacea), Annellata (Chaeto p ods and Leeches), Cirripedia.

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  • He upset (1830) Cuvier's retention of the Cirripedes among Mollusca, and his subsequent treatment of them as an isolated class, by showing that they begin life as free-swimming Crustacea identical with the young forms of other Crustacea.

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  • Classes: Crustacea, Arachnida,Myriapoda,Insecta,Chaetognatha, Annelida.

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  • Fritz Muller, by his studies on Crustacea (Fiir Darwin, 1864), showed the way in which genealogical theory may be applied to the minute study of a limited group.

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  • Dana on Zoophytes (1846), Geology (1849) and Crustacea (2 vols., 1852-1854).

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  • Udonella occurs on parasitic Crustacea).

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  • In Japan, as elsewhere, the principal crustacea are found in the sea.

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  • This Makuzu faience, produced by the now justly celebrated Miyagawa ShOzan of Ota (near Yokohama), survives in the form of vases and pots having birds, reptiles, flowers, crustacea and so forth plastered over the surfacespecimens that disgrace the period of their manufacture, and represent probably the worst aberration of Japanese ceramic conception.

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  • Malta has several species of zoophytes, sponges, mollusca and crustacea.

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  • Pure calcareous sand and calcareous mud are formed by wave action on the shores of coral islands where the only material available is coral and the accompanying calcareous algae, crustacea, molluscs and other organisms secreting carbonate of lime.

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  • SHRIMP, a name applied in general to the smaller crustacea of the order Macrura and in particular to an edible species found on the coasts of northern Europe (Crangon vulgaris).

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  • The larger shrimp-like crustacea are generally known as "prawns," the name being especially applied in Britain to the species Leander serratus, formerly called Palaemon serratus, which is highly esteemed for the table.

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  • Under the heading Crustacea the Entomostraca have already been distinguished not only from the Thyrostraca or Cirripedes, but also from the Malacostraca, and an intermediate group of which the true position is still disputed.

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  • Though the exterior is more uniform than in most groups of Crustacea, the bivalved shell or carapace may be strongly calcified and diversely sculptured (fig.

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  • p. 211 (1901); Sars, Crustacea of Norway, vol.

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  • Medusae capture their prey, consisting of small organisms of various kinds, especially Crustacea, by means of the tentacles which hang out like fishing-lines in all directions.

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  • The mouth opens through a narrow pharynx (p) into a chamber which is (as in Crustacea) at once crop and gizzard, the mastax (ma), whose thickenings are imbedded in the posteroventral wall.

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  • are twice as long as the 3to 5-toothed Thus the crop-gizzard unci; c, virgate - mallei rod-like, manubria has the same comand fulcrum very long, unci Ior 2-toothed; bination of structures d forcipate - rami large and used as a foras we find in the ceps, mallei rod-like, unci pointed or evanstomach of higher escent; e, incudate - stout fulcrum, rami Crustacea, with which formingaforceps, mallei evanescent; f, unwe may call it homocinate - unci large, 2-toothed, manubria plastic. The trophi evanescent, incus slender; g, ramate - rami are (I) a median incus subquadrantic, fulcrum rudimentary, manY - shaped, with the ubria evanescent; h,malleo-ramate - mallei (fulcrum) distal fastened by their unci to the rami, manubria foot and the arms (rami) looped, rami large and fulcrum slender.

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  • The Rotifera are all aquatic, the majority dwelling in fresh water with Protozoa and Protophyta, as well as Entomostracous Crustacea.

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  • TRILOBITES, extinct Arthropoda, formerly classified with the Crustacea, but of late years relegated to the Arachnida, which occurred abundantly in seas of the Cambrian and Silurian periods, but disappeared entirely at the close of the Palaeozoic epoch.

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  • ,Among the known fossils are vermes, crustacea and probably brachiopods and pteropods The character of the sediments of the Proterozoic is such as to show that mature weathering affected the older rocks before their material was worked over into the Proterozoic formations.

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  • Certain other remarkable crustacea, however, had made their appearance, especially in connection with the Salina series of the east.

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  • The life of the land waters was also noteworthy, especially for the great deployment of what may be called the crustacean-ostracodermo-vertebrate group. The crustacea were represented by eurypterids, the ostracoderms by numerous strange, vertebrate-like forms (Cephalaspis, Gyathaspis, Trematopsis, Bothriolepss, &c.), and the vertebrates by a great variety of fishes, The land life of the period is represented more fully among the fossils than that of any preceding period.

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  • Their affinities with the lower Crustacea were recognized by Cuvier and his contemporaries, but it was one of the brilliant discoveries of that remarkable and too-little-honoured naturalist, J.

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  • Vaughan Thompson, of Cork, which decided their position as Crustacea.

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  • Thus the condition in the Dermaptera is more primitive than in any other Pterygote order except the Ephemeroptera (Mayflies) which are still more generalized, the primitive mesodermal ducts (oviducts and vasa deferentia) opening by paired apertures as in the Crustacea.

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  • Albinism is restricted to no particular class of the animal kingdom; for partial albinism at least is known to occur in Coelentera, worms, Crustacea, Myriapoda, Coleoptera,Arachnida and fishes.

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  • The inhabitants of the waters of this geographical phase include mollusca, which are supposed to have lived in brackish or fresh water, such as Anthracomya, Naiadites, Carbonicola, and many forms of Crustacea, e.g.

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  • This estuary they called the Rio dos Camaroes (the river of Prawns), from the 2 abundance of the crustacea found therein.

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  • Crustacea occupied an extremely prominent place; there were Phyllocarids such as Hymenocaris, and Ostracods like Entomidella; but by far the most important in numbers and development were the Trilo bites, now extinct, but in palaeozoic times so abundant.

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  • Under this zoological title are included several groups of Crustacea, united by characters which attest their common origin, though some, and probably all of them, were already separated in distant geological ages, and some have now attained a peculiar isolation.

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  • New light, however, has been thrown upon the "intellectual" capacity of Crustacea by the proof that the spider-crabs deliberately use changes of raiment to harmonize with their surroundings, donning and doffing various natural objects as we do our manufactured clothes.

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  • A bibliography of the order is given in that author's Crustacea of Norway, vol.

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  • It adapts itself to parasitic life not only in fishes, but in its own class Crustacea, and that in species of every order, its own included.

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  • The order has been divided into seven tribes, of which a fuller summary than can here be given will be found in Stebbing, History of Crustacea (1893).

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  • Hansen (1890); Isopoda Terrestria, Budde-Lund (1885); Bopyridae, Bonnier (1900); Crustacea of Norway, vol.

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  • xxviii., and supplementary notices in Della Valle's Monograph of the Gammarini (1893)', the scope of his work, however, not covering the Hyperiidea and Oxycephalidae of Bovallius (1889, 1890); but since these dates very numerous additions to the literature have been made by Birula, Bonnier, Norman, Walker and others, especially the Crustacea of Norway, vol.

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  • APTERA (Greek for "wingless"), a term in zoological classification applied by Linnaeus to various groups of wingless arthropods, including some of the insects, the centipedes, the millipedes, the Arachnida (scorpions, spiders, &c.) and the Crustacea.

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  • i, Mn.; 4), with toothed apex and sub-apical grinding surface, like those of certain Crustacea; by the presence between the mandibles and maxillae of a pair of appendages (superlinguae or maxil ' x lulae), fig.

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  • They are distributed thus: Vertebrata, 8 species; Insecta, 17; Arachnida, 12; Myriapoda, 2; Crustacea, 5; Vermes, 3; Mollusca, 1.

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  • CRUSTACEA, a very large division of the animal kingdom, comprising the familiar crabs, lobsters, crayfish, shrimps and prawns, the sandhoppers and woodlice, the strangely modified barnacles and the minute water-fleas.

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  • In point of size also the Crustacea vary within very wide limits.

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  • The habits of the Crustacea are no less diversified than their structure.

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  • Apart from the numerous parasitic forms, the only Crustacea which have adopted a strictly sedentary habit of life are the Cirripedia, and here, as elsewhere, profound modifications of structure have resulted, leading ultimately to a partial assumption of the radial type of symmetry which is so often associated with a sedentary life.

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  • Many, perhaps the majority, of the Crustacea are omnivorous or carrion-feeders, but many are actively predatory in their habits, and are provided with more or less complex and efficient instruments for capturing their prey, and there are also many planteaters.

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  • Perhaps the most complete degeneration is found in the Rhizocephala, which are parasitic on other Crustacea.

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  • Many of the larger species of Crustacea are used as food by man, the most valuable being the lobster, which is caught in large quantities on both sides of the North Altantic. Perhaps the most important of all Crustacea, however, with respect to the part which they play in the economy of nature, are the minute pelagic Copepoda, of which incalculable myriads form an important constituent of the " plankton " in all the seas of the globe.

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  • The application of the morphological method to the Crustacea may perhaps be dated from the work of J.

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  • Vaughan Thompson demonstrated the existence of metamorphosis in the development of the higher Crustacea.

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  • It is noteworthy that even at this late date the Cirripedia (Thyrostraca) were still excluded from the Crustacea, though Darwin's Monograph (1851-1854) was soon to make them known with a wealth of anatomical and systematic detail such as was available, at that time, for few other groups of Crustacea.

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  • In more recent years the long and constantly increasing list of writers on Crustacea contains no name more honoured than that of the veteran G.

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  • It is quite probable, however, that in the primitive ancestors of existing Crustacea a still smaller number of somites formed the head.

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  • A character which recurs in the most diverse groups of the Crustacea, and which is probably to be regarded as a primitive attribute FIG.

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  • It seems likely that a similar explanation is to be applied to the coalescence of one or two trunk-somites with the head in the Copepoda, and, if this be so, the only Crustacea remaining in which no trace of a shell-fold is found in the adult are the Anostracous Phyllopoda such as Branchipus (fig.

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  • - Amid the great variety of forms assumed by the appendages of the Crustacea, it is possible to trace, more or less plainly, the modifications of a fundamental type consisting of a peduncle, the protopodite, bearing two branches, the endopodite and exopodite.

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  • The Phyllopoda are the only Crustacea in which distinct and functional gnathobasic processes are found on appendages far removed from the mouth.

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  • The two distal endites are regarded as corresponding to the endopodite and exopodite of the higher Crustacea, the axis or corm of the Phyllopod limb representing the protopodite.

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  • It is not altogether easy to recognize the homologies of the endites and exites even within the order Phyllopoda, and the identification of the two distal endites as corresponding to the endopodite and exopodite of higher Crustacea is not free from difficulty.

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  • In many Crustacea the eyes are borne on stalks which are movably articulated with the head and which may be divided into two or three segments.

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  • In the great majority of Crustacea the antennules are purely sensory in function and carry numerous " olfactory " hairs.

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  • The antennae (second antennae) are of special interest on account of the clear evidence that, although preoral in position in all adult Crustacea, they were originally postoral appendages.

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  • In almost all Crustacea the food-canal runs straight through the body, except at its anterior end, where it curves downwards to the ventrally-placed mouth.

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  • As in the other Arthropoda, the circulatory system in Crustacea is largely 1 6/ lacunar, the blood flowing in spaces or channels without definite walls.

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  • The most important excretory or renal organs of the Crustacea are two pairs of glands lying at the base of the antennae and of the second maxillae respectively.

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  • In addition to these two pairs of glands, which are in all probability the survivors of a series of segmentally arranged coelomoducts present in the primitive Arthropoda, other excretory organs have been described in various Crustacea.

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  • The eyes of Crustacea are of two kinds, the unpaired, median or "nauplius " eye, and the paired compound eyes.

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  • Mention should also be made of the partial or complete atrophy of the eyes in many Crustacea which live in darkness, either in the deep sea or in subterranean habitats.

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  • Recent observations, however, make it very doubtful whether aquatic Crustacea can hear at all, in the proper sense of the term, and it has been shown that one function, at least, of the so-called otocysts is connected with the equilibration of the body.

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  • In nearly all Crustacea the antennules and often also the antennae bear groups of hair-like filaments in which the chitinous cuticle is extremely delicate and which do not taper to a point but end bluntly.

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  • In addition to the digestive and excretory glands already mentioned, various glandular structures occur in the different groups of Crustacea.

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  • - Many Crustacea belonging to very different groups (Ostracoda, Copepoda, Schizopoda, Decapoda) possess the power of emitting light.

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  • In the great majority of Crustacea the sexes are separate.

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  • Very few Crustacea are viviparous in the sense that the eggs are retained within the body until hatching takes place (some Phyllopoda), but, on the other hand, the great majority carry the eggs in some way or other after their extrusion.

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  • The majority of the Crustacea are hatched from the egg in a form differing more or less from that of the adult, and pass through a series of free-swimming larval stages.

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  • They are of interest, however, rather from the point of view of general embryology than from that of the special student of the Crustacea, and cannot be fully dealt with here.

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  • The larval metamorphoses of the Crustacea have attracted much attention, and have been the subject of much discussion in view of their bearing on the phyiogenetic history of the group. In those Crustacea in which the series of larval stages is most complete, the starting-point is the form already mentioned under the name of nauplius.

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  • In most of the Crustacea which hatch at a later stage there is, as already mentioned, more or less clear evidence of an embryonic nauplius stage.

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  • In most Crustacea, however, this primitive scheme is more or less modified.

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  • Although fossil remains of Crustacea are abundant, from the most ancient fossiliferous rocks down to the most recent, their study has hitherto contributed little to a precise knowledge of the phylogenetic history of the class.

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  • In the dearth of trustworthy evidence as to the actual forerunners of existing Crustacea, we are compelled to rely wholly FIG.

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  • The first attempts to reconstruct the genealogical history of the Crustacea started from the assumption that the " theory of recapitulation " could be applied to their larval history.

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  • As regards the nauplius, however, the constancy of its general character in the most widely diverse groups of Crustacea strongly suggests that it is a very ancient type, and the view has been advocated that the Crustacea must have arisen from an unsegmented nauplius-like ancestor.

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  • The resemblances between the Crustacea and the Annelid worms, in such characters as the structure of the nervous system and the mode of growth of the somites, can hardly be ignored.

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  • 5, 3, Eryon arctiformis, Schl.; Lithographic stone, Solen6, stock of the Crustacea, such as the paired eyes and the shell-fold, are not present in the nauplius.

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  • In those Copepods in which the palps of the mandibles as well as the antennae are biramous and natatory, the first three pairs of appendages retain throughout life, with little modification, the shape and function which they have in the nauplius stage, and must, in all likelihood, be regarded as approximating to those of the primitive Crustacea.

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  • The probable course of evolution of the different groups of Crustacea from this hypothetical ancestral form can only be touched on here.

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  • The modern classification of Crustacea may be said to have been founded by P. A.

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  • Class Crustacea.

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  • Crustacea and fish abound on the reefs.

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  • BARNACLE, a name applied to Crustacea of the division Cirripedia or Thyrostraca.

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  • His earlier publications were on zoology; he dealt with the Amphibia (1839), Reptiles (1840), with Mollusca and Crustacea (1845) and more generally with the invertebrate fauna of the Mediterranean (1854).

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  • The names Condylopoda and Gnathopoda have been subsequently proposed for the same group. The word refers to the jointing of the chitinized exo-skeleton of the limbs or lateral appendages of the animals included, which are, roughly speaking, the Crustacea, Arachnida, Hexapoda (so-called " true insects "), Centipedes and Millipedes.

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  • Lamarck's penetrating genius is chiefly responsible for the shrinkage of the word Insecta, since it was he who, forty years after Linnaeus's death, set up and named the two great classes Crustacea and Arachnida (included by Linnaeus under Insecta as the order " Aptera "), assigning to them equal rank with the remaining Insecta of Linnaeus, for which he proposed the very appropriate class-name " Hexapoda."

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  • Lamarck, however, appears not to have insisted on this name Hexapoda, and so the class of Pterygote Hexapods came to retain the group-name Insecta, which is, historically or etymologically, no more appropriate to them than it is to the classes Crustacea and Arachnida.

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  • 8) of the marine branchiate worms are the same things genetically as the " legs " of Crustacea and Insects (figs.

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  • The orders included in the various classes are not discussed here, but are treated of under the following titles: - Peripatus (Onychophora), Centipede and Millipede (Myriapoda), Hexapoda (Insecta), Arachnida and Crustacea.

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  • Lankester (2) was the first to suggest that (as is actually the fact in the Nauplius larva of the Crustacea) the prae-oral somites or prosthomeres and their appendages were ancestrally postoral, but have become prae-oral " by adaptational shifting of the oral aperture."

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  • (After Goodrich.) The Crustacea (fig.

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  • The three prosthomeres or prae-oral somites of Crustacea due to the sinking back of the mouth one somite farther than in Arachnida are not clearly indicated by coelomic cavities in the embryo, but their existence is clearly established by the development and position of the appendages and by the neuromeres.

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  • The eyes in some Crustacea are mounted on articulated stalks, and from the fact that they can after injury be replaced by antennalike appendages it is inferred that they represent the parapodia of the most anterior prosthomere.

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  • The Crustacea are tetartognathous.

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  • As in Crustacea and Arachnida, FIG.

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  • The existence of this third prosthomere corresponding to the third prosthomere of the Crustacea is a strong argument for the derivation of the Hexapoda, and with them the Chilopoda, from some offshoot of the Crustacean stem or class.

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  • The buccal somite, with its mandibles, is in Hexapoda, as in Crustacea, the fourth: they are tetartognathous.

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  • In Crustacea the fourth or mandibular somite never has less than the two following somites associated with it by the adaptation of their appendages as jaws, and the ankylosis of their terga with that of the prosthomeres.

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  • But in higher Crustacea the cephalic " tagma " is extended, and more somites are added to the fusion, and their appendages adapted as jaws of a kind.

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  • 7) - thus six in all (as in some Crustacea), including prosthomeres, all ankylosed by their terga to form a cephalic shield.

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  • Lankester (5) has shown (and his views have been accepted by Professors Korschelt and Heider in their treatise on Embryology) that the limb of the lowest Crustacea, such as Apus, consists of a corm or axis which may be jointed, and gives rise to outgrowths, either leaf-like or filiform, on its inner and outer margins (endites and exites).

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  • It is by the specialization of two " endites " that the endopodite and exopodite of higher Crustacea are formed, whilst a flabelliform exite is the homogen or genetic equivalent of the epipodite (see Lankester, " Observations and Reflections on Apus Cancriformis," Q.

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  • It is not true that all the biting processes of the Arthropod limb are thus produced - for instance, the jaws of Peripatus are formed by the axis or corm itself, whilst the poisonjaws of Chilopods, as also their maxillae, appear to be formed rather by the apex or terminal region of the ramus of the limb; but the opposing jaws (= hemignaths) of Crustacea, Arachnida and Hexapoda are gnathobases, and not the axis or corm.

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  • to) becomes in Crustacea the " walking leg " of the mid-region of the body; it becomes the palp or jointed process of anterior segments.

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  • Such chelate rami or limbbranchesare independently developed in Crustacea and inArachnida, and are carried by somites of the body which do not correspond in position in the two groups.

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  • A, A walking leg; p ' to p 4, Since the eye-stalks of Podophthalthe characteristic " pads "; f, mate Crustacea represent appendthe foot; cl', c1 2, the two ages, we are forced to the conclusion claws.

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  • that the sessile eyes of other B, An oral papilla, one of Crustacea, and of other Arthropoda the second pair of post-oral generally, indicate the position of appendages.

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  • Milne-Edwards, who was followed by Huxley, long ago formulated the conclusion that the eye-stalks of Crustacea are modified appendages, basing his argument on a specimen of Palinurus (figured in Bateson's book (1), in which the eye-stalk of one side is replaced by an antenniform palp. Hofer (6) in 1894 described a similar case in Astacus.

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  • (4) Three of the rami of the primitive limb (endites 5 and 6, and exite I) specially developed as endopodite, exopodite, and epipodite - the first two often as firm and strongly chitinized, segmented, leg-like structures; the original axis or corm reduced to a basal piece, with or without a distinct gnathobase (endite i)- typical tri-ramose limb of higher Crustacea.

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  • This may be filiform or brush-like or lamellate when it is an antenna or palp; a simple spike (walking leg of Crustacea, of other aquatic forms, and of Chilopods and Diplopods); the terminal joint flattened (swimming leg of Crustacea and Gigantostraca); the terminal joint provided with two or with three recurved claws (walking leg of many terrestrial forms - e.g.

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  • En s, The rudimentary sixth endite (exopodite of higher Crustacea).

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  • This is the typical " bi-ramose limb " often found in Crustacea.

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  • The rami may be flattened for swimming, when it is " a bi-ramose swimmeret," or both or only one may be filiform and finely annulate; this is the form often presented by the antennae of Crustacea, and rarely by prae-oral appendages in other Arthropods.

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  • The endopodite may be retained as a small segmented palp at the side of the gnathobase or disappear (mandible of Crustacea, Chilopoda and Hexapods).

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  • Its jointing (segmentation) may be retained, but its rami disappear (Podophthalmous Crustacea).

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  • (io) The forms assumed by special modification of the elements of the parapodium in the maxillae, labium, &c., of Hexapods, Chilopods, Diplopods, and of various Crustacea, deserve special enumeration, but cannot be dealt with without ample space and illustration.

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  • It seems probable that there are branchial plumes or filaments in some Arthropoda (some Crustacea) which can be identified with the distinct branchial organs of Chaetopoda, which lie dorsal of the parapodia and are not part of the parapodium.

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  • In Crustacea and Hexapoda of all grades we find compound eyes with the more complicated ommatidia described above.

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  • But they seem to point to a community of origin of Hexapods and Crustacea in regard to the complicated ommatidia of the compound eye, and to a certain isolation of the Arachnida, which are, however, traceable, so far as the eyes are concerned, to a distant common origin with Crustacea and Hexapoda through the very simple compound eyes (monostichous, polymeniscous) of Limulus.

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  • - Diagram to show the derivation of the unit or "ommatidium " of the compound eye of Crustacea and Hexapoda, C, from a simple monomeniscous monostichous eye resembling the lateral eye of a scorpion, A, or the unit of the compound lateral eye of Limulus (see article Arachnida, figs.

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  • The Malpighian tubes of Hexapods are outgrowths of the proctodaeum, but those of Scorpion and the Amphipod Crustacea are part of the metenteron or endodermal gut, though originating near its junction with the proctodaeum.

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  • The absence of such renal caeca in Limulus and their presence in the terrestrial Arachnida is precisely on a parallel with their absence in aquatic Crustacea and their presence in the feebly branchiate Amphipoda.

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  • (Compare the definition of the class Chilopoda.) The movement of the legs in Diplopoda is like that of those of Peripatus, of the Phyllopod Crustacea, and of the parapodia of Chaetopoda, symmetrical and identical on the two sides of the body.

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  • No tracheate Crustacea are known, but some terrestrial Isopoda develop pulmonary in-sinkings of the integument.

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  • The lateral eyes of Crustacea are polymeniscous, with highly specialized retinulae like those of Hexapoda, and unlike the simpler compound lateral eyes of lower Arachnida.

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  • The Crustacea exhibit a longer and more complete series of forms than any other class of Arthropoda, and may be regarded as preserving the most completely represented line of descent.

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  • The first prosthomere has its appendages represented by the compound eyes and a protocerebrum, the second has the antennae for its appendages and a deutocerebral neuromere, the third has suffered suppression of its appendages (which corresponded to the second pair of antennae of Crustacea), but has a tritocerebrum and coelomic chamber.

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  • The number is significant, since it agrees with that found in Edriophthalmous Crustacea, and assigns the labium of the Hexapod to the same somite numerically as that which carries the labium-like maxillipedes of those Crustacea.

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  • It appears from observation of the embryo that whilst the first prosthomere of Centipedes has its appendages reduced and represented only by eye-patches (as in Arachnida, Crustacea and Hexapoda), the second has a rudimentary antenna, which disappears, whilst the third carries the permanent antennae, which accordingly correspond to the second antennae of Crustacea, and are absent in Hexapoda.

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  • twenty-one somites in all (as in the higher Crustacea).

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  • The Hexapoda are not only all confined to a very definite disposition of the somites, appendages and apertures, as thus indicated, but in other characters also they present the specialization of a narrowly-limited highly-developed order of such a class as the Crustacea rather than a range from lower more generalized to higher more specialized forms such as that group and also the Arachnida present.

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  • The lateral eyes of Hexapoda, like those of Crustacea, belong to the most specialized type of " compound eye," found only in these two classes.

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  • Our general conclusion from a survey of the Arthropoda amounts to this, that whilst Peripatus, the Diplopoda, and the Arachnida represent terrestrial offshoots from successive lower grades of primitive aquatic Arthropoda which are extinct, the Crustacea alone present a fairly full series of representatives leading upwards from unspecialized forms. The latter were not very far removed from the aquatic ancestors (Trilobites) of the Arachnida, but differed essentially from them by the higher specialization of the head.

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  • On the other hand, the facts that the Hexapoda and the Chilopoda have triprosthomerous heads, that the Hexapoda have the same total number of somites as the nomomeristic Crustacea, and the same number of opisthomeres in the head as the more terrestrial Crustacea, together with the same adaptation of the form of important appendages in corresponding somites, and that the compound eyes of both Crustacea and Hexapoda are extremely specialized and elaborate in structure and identical in that structure, all lead to the suggestion that the Hexapoda, and with them, at no distant point, the Chilopoda, have branched off from the Crustacean main stem as specialized terrestrial lines of descent.

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  • And it seems probable that in the case of the Hexapoda, at any rate, the point of departure was subsequent to the attainment of the nomomeristic character presented by the higher grade of Crustacea.

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  • It ranges from Iceland to the shores of the Red Sea, and lives chiefly on marine worms, crustacea and such molluscs as it is able to obtain.

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  • The manioc root is also largely consumed, together with several other roots and vegetables; but little animal foods (save fish and freshwater Crustacea) is taken by the mass of the people except at festival times.

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  • THYROSTRACA, an order of Crustacea, comprising barnacles, acorn shells and some allied degenerate parasites.

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  • In strong contrast with the condition in most Crustacea, the spermatozoa are mobile.

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  • Studer (Crustacea of the Gazelle, 1882) records Balanus amphitrite (Darwin?) from roots and stems of mangroves in the Congo, where, he says, " it follows the mangroves as far as their vegetation extends along the stream, to six sea-miles from the mouth."

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  • The compactness of the class Crustacea is generally admitted; of the precise affinities of its subdivisions there is still much to learn.

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