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.
A near relationship between the Apterygota and the Crustacea has been ably advocated by H.
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.
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.
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."
Ray's "Insects" comprised the Arachnids, Crustacea, Myriapoda and Annelida, in addition to the Hexapods.
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.
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).
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.
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.
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.
Limulus thus agrees with Scorpio and differs from the Crustacea, in which there are three prosthomeres - one ocular and two carrying palpiform appendages.
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.
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.
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.
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.
In the specialized ommatidia of the compound eyes of Crustacea and Hexapods the rhabdom is an important structure.'
Possibly, however, an investigation of the development of the median eyes of some Crustacea(Apus,Palaemon)may prove them to be diplostichous in origin.
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.
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.
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.
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.
The Crustacea never have more than one pair.
This is a very definite and remarkable agreement, since such a reticular gonocoel is not found in Crustacea (except in the male Apus).
The Crustacea are - with the exception of the Cirrhipedia - remarkable for having stiff, motionless spermatozoids.
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.
(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.
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.
The great Arthropod class, the Crustacea, presents to the zoologist at the present day an immense range of forms,.
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.
This fact renders their association with the Crustacea impossible, if classification is to be the expression of genetic affinity inferred from structural coincidence.
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.
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.
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.
This estuary they called the Rio dos Camaroes (the river of Prawns), from the 2 abundance of the crustacea found therein.
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.
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.
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.
,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.
Certain other remarkable crustacea, however, had made their appearance, especially in connection with the Salina series of the east.
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.
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.