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arthropoda

arthropoda Sentence Examples

  • The body consists of a number of exactly similar or closely similar segments, which are never fused and metamorphosed, as in the Arthropoda, to form specialized regions of the body.

  • Where locomotive appendages (the parapodia of the Polychaeta) exist, they are never jointed, as always in the Arthropoda; nor are they modified anteriorly to form jaws, as in that group.

  • These muscles are not striated, as they are in the Arthropoda.

  • Thus in the Chaetopoda the perivisceral cavity is coelomic; in this respect the group contrasts with the Arthropoda and Molluscs, where the perivisceral cavity is, mainly at least, part of the vascular or haemal system, and agrees with the Vertebrata.

  • The plan of the central nervous system is therefore that of the Arthropoda.

  • The cerebral ganglia constitute an archicerebrum for the most part, there being no evidence that, as in the Arthropoda, a movement forward of post-oral ganglia has taken place.

  • von Siebold's (1848) name of Arthropoda.

  • And the wings, though not always present, are highly characteristic of the Hexapoda, since no other group of the Arthropoda has acquired the power of flight.

  • In all main points of their internal structure the Hexapoda agree with other Arthropoda.

  • The nature of these organs is described in the article Arthropoda.

  • r remarkable type of bloodsystem characterizing the Arthropoda.

  • Lecaillon (1898) on various leaf beetles, tend to show that the organ " in the embryos of the lower Arthropoda corresponds with whole of the " mid-gut " arises from the proliferation of cells at the the region invaginated to form the serosa of the hexapod embryo.

  • 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.

  • Relationships And Phylogeny The Hexapoda form a very clearly defined class of the Arthropoda, and many recent writers have suggested that they must have arisen independently of other Arthropods from annelid worms, and that the Arthropoda must, therefore, be regarded as an " unnatural," polyphyletic assemblage.

  • The cogent arguments against this view are set forth in the article on Arthropoda.

  • of the animals included in the class Hexapoda of the great phylum (or sub-phylum) Arthropoda.

  • In 1735 appeared the first edition of the Systema naturae of Linnaeus, in which the "Insecta" form a group equivalent to the Arthropoda of modern zoologists, and are divided into seven orders, whose names - Coleoptera, Diptera, Lepidoptera, &c., founded on the nature of the wings - have become firmly established.

  • The Insecta of Linnaeus was a group exactly equivalent to the Arthropoda founded a hundred years later by Siebold and Stannius.

  • The position of the Arachnida in the great sub-phylum Arthropoda, according to recent anatomical and embryological researches, is explained in the article Arthropoda.

  • But it is necessary to remember, in the light of recent discoveries, that the sixth prosomatic pair of appendages is carried on the seventh somite of the whole series, there being two prosthomeres or somites in front of the mouth, the first carrying the eyes, the second the chelicerae; also that the first mesosomatic or genital somite is not the seventh or even the eighth of the whole series of somites which have been historically present, 1 See the article Arthropoda for the use of the term " prosthomere."

  • 12 in the article Arthropoda.

  • The genital ducts of Arthropoda are, like the green glands, shell glands and coxal glands, to be regarded as coelomoducts (gonocoels).

  • We know that such a lateral position of the nerve cords preceded the median position in both Arthropoda and Chaetopoda.

  • It seems that there is a primitive tendency in the Arthropoda for the arteries to accompany the nerve cords, and a " supra-spinal " artery - that is to say, an artery in close relation to the ventral nerve cords--has been described in several cases.

  • It is very probable that in Scorpio they do not serve merely to secrete a digestive fluid (shown in other Arthropoda to resemble the pancreatic fluid), but that they also become distended by the juices of the prey sucked in by the scorpion - as certainly must occur in the case of the simple unbranched gastric caeca of the spiders.

  • In Limulus Lankester found (15) the spermatozoa to possess active flagelliform " tails," and to resemble very closely those of Scorpio which, as are those of most terrestrial Arthropoda, are actively motile.

  • We have now passed in review the principal structural features in which Limulus agrees with Scorpio and differs from other Arthropoda.

  • (From Lankester, loc. cit., after Packard.) with all air-breathing Arthropoda except Peripatus, possesses these tubules, which are often called Malpighian tubes.

  • In fact it is not possible to maintain that the renal excretory tubes of the gut are of one common origin in the Arthropoda.

  • 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.

  • Further, it is pointed out by Korschelt and Heider that the hinder portion of the gut frequently acts in Arthropoda as an organ of nitrogenous excretion in the absence of any special excretory tubules, and that the production of such caeca from its surface in separate lines of descent does not involve any elaborate or unlikely process of growth.

  • When we consider the relationships of the various classes of Arthropoda, having accepted and established the fact of the close genetic affinity of Limulus and Scorpio, we are led to important conclusions.

  • It has been insisted, by those who accepted Lankester's original doctrine of the direct or genetic affinity of the Chaetopoda and Arthropoda, that Apus and Branchipus really come very near to the ancestral forms which connected those two great branches of Appendiculate (Parapodiate) animals.

  • (From Korschelt and Heider.) quently take place (as in all Arthropoda) at the posterior extremity of the body, whilst excalation of somites may occur at the constricted areas which often separate adjacent " regions," though there are very few instances in which it has been recognized.

  • Claus, " Degeneration of the Acari and Classification of Arthropoda," Anzeiger d.

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

  • Arthropoda.

  • the Rotifera, the Chaetopoda and the Arthropoda.

  • Sub-phyla: Rotifera, Chaetopoda, Arthropoda.

  • Arthropoda (q.v.).

  • (See ARTHROPODA.)

  • Annelids are segmented worms, and differ from the Arthropoda, which they closely resemble in many respects, by the possession of a portion of the coelom traversed by the alimentary canal.

  • Yet in the next family Alonella nana (Baird) disputes the palm and claims to be the smallest of all known Arthropoda.

  • 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.

  • 21), so that its fibres join the anterior faces of the nerve-end cells as in Vertebrates, instead of their posterior faces as in the cephalic eyes of Mollusca and Arthropoda; moreover, the lens is not a cuticular product but a cellular structure, which, again, is a feature of agreement with the Vertebrate FIG.

  • The perioesophageal nerve-ring of Chaetopoda and Arthropoda is represented, not by the collar first mentioned in the above description, but by the commissures connecting the cerebral and pedal ganglia.

  • (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart.

  • Experiments to test distastefulness have also been made with various kinds of insectivorous Arthropoda, like spiders and mantises.

  • Among the remaining divisions of Invertebrata special mention may be made of the air-breathing Arthropoda - on the whole the most important and interesting group. About one-third of the animals belonging thereto that occur in the higher regions are exclusively alpine (or alpine and northern); these characteristically alpine forms being furnished chiefly by the spiders, beetles and butterflies.

  • The animals thus associated, the Rotifera, Chaetopoda and Arthropoda, are composed of a larger or smaller number of hollow rings, each ring possessing typically a pair of hollow lateral appendages, moved by intrinsic muscles and penetrated by blood-spaces.

  • Arthropoda are very abundant and as yet little known.

  • Collectively, they are ranked as one of the classes forming the sub-phylum Arthropoda, and their distinguishing characters are discussed under that heading.

  • It will be sufficient here to define them as Arthropoda for the most part of aquatic habits, having typically two pairs of antenniform appendages in front of the mouth and at least three pairs of post-oral limbs acting as jaws.

  • - As in all Arthropoda the body consists of a series of segments or somites which may be free or more or less coalesced together.

  • As in all Arthropoda, it is composed of three divisions, a fore-gut or stomodaeum, ectodermal in origin and lined by an inturning of the chitinous cuticle, a mid-gut formed by endoderm and without a cuticular lining, and a hind-gut or proctodaeum, which, like the fore-gut, is ectodermal and is lined by cuticle.

  • 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.

  • There is every reason to believe 2, Gastric teeth of common that, in the primitive Arthropoda, lobster, Homarus vulgaris.

  • A very remarkable condition of the blood-system, unique, as far as is yet known among the Arthropoda, is found in a few genera of parasitic Copepoda (Lernanthropus, Mytilicola).

  • 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.

  • The central nervous system is constructed on the same general plan as in the other Arthropoda, consisting of a supra-oesophageal ganglionic mass or brain, united by circumoesophageal connectives with a double ventral chain of segmentally arranged ganglia.

  • As in Arthropoda, the hairs or setae on the surface of the body are important organs of sense and are variously modified for special sensory functions.

  • The gonads, as in other Arthropoda, are hollow saccular organs, the cavity communicating with the efferent ducts.

  • The definition just quoted might include all animals belonging to the groups of the Arthropoda and Annelida, and U.

  • The class Insecta of Linnaeus (1758) was coextensive with the Arthropoda of modern zoologists.

  • For a general account of the structure, development and relationships of insects, see Arthropoda and Hexapoda, while details of the form, habits and classification of insects will be found in articles on the various orders or groups of orders (Aptera, Coleoptera, Dipteria,Hemiptera,Hymenoptera,Lepidoptera,Neuroptera, Orthoptera, Thysanoptera), and in special articles on the more familiar divisions (ANT, BEE, Dragon-Fly, Earwig, &c.).

  • GNATHOPODA, a term in zoological classification, suggested as an alternative name for the group Arthropoda.

  • ARTHROPODA, a name, denoting the possession by certain animals of jointed limbs, now applied to one of the three sub-phyla into which one of the great phyla (or primary branches) of coelomocoelous animals - the Appendiculata - is divided; the other two being respectively the Chaetopoda and the Rotifera.

  • The word "Arthropoda " was first used in classification by Siebold and Stannius (Lehrbuch der vergleich.

  • We have, in fact, returned very nearly to Cuvier's conception of a great division or branch, which he called Articulata, including the Arthropoda and the Chaetopoda (Annelides of Lamarck, a name adopted by Cuvier), and differing from it only by the inclusion of the Rotif era.

  • The 1 The group Arthropoda itself,th usconstituted,wasprecisely identical in its area with the Insecta of Linnaeus, the Entoma of Aristotle.

  • Hence the term Appendiculata was introduced by Lankester (preface to the English edition of Gegenbaur's Comparative Anatomy, 1878) to indicate the group. The relationships of the Arthropoda thus stated are shown in the subjoined table: - (Sub-phylum r.

  • There are other remarkable and distinctive features of structure which hold the Arthropoda together, and render it impossible to conceive of them as having a polyphyletic origin, that is to say, as having originated separately by two or three distinct lines of descent from lower animals; and, on the contrary, establish the view that they have been developed from a single line of primitive Gnathopods which arose by modification of parapodiate annulate worms not very unlike some of the existing Chaetopods.

  • (2) In all existing Arthropoda the region in front of the mouth is no longer formed by the primitive prostomium or head-lobe, but one or more segments, originally post-oral, with their appendages have passed in front of the mouth (prosthomeres).

  • Tabular Statement of the Grades, Classes and Sub-classes of the Arthropoda.

  • - It will be convenient now to give in the clearest form a statement of the larger subdivisions of the Arthropoda which it seems necessary to recognize at the present day.

  • SUB-Phylum Arthropoda (of the Phylum Appendiculata).

  • Hyparthropoda (hypothetical forms connecting ancestors of Chaetopoda with those of Arthropoda).

  • The body of the Arthropoda is more or less clearly divided into a series of rings, segments, or somites which can be shown to be repetitions one of another, possessing identical parts and organs which may be larger or smaller, modified in shape or altogether suppressed in one somite as compared with another.

  • The Arthropoda are all distinguished from, The prostomial the Chaetopoda by the fact that the head A ganglion-mass or consists of one or more somites which lie in archi cerebrum.

  • It was conceived by Huxley, among others, that the same number of cephalic somites would be found to be characteristic of all the diverse classes of Arthropoda, and that the somites, not only of the head but of the various regions of the body, could be closely compared in their numerical sequence in classes so distinct as the Hexapods, Crustaceans and Arachnids.

  • that all the Arthropoda are to be traced to a common ancestor resembling a Chaetopod worm, but differing from it in having lost its chaetae and in having a prosthomere in front of the mouth (instead of prostomium only) and a pair of hemignaths (mandibles) on the parapodia of the buccal somite.

  • It has taken some time to obtain any general acceptance of the view that the parapodia of the Chaetopoda and the limbs of Arthropoda are genetically identi cal structures; yet if we compare the para podium of Tomopteris or of Phyllodoce with one of the foliaceous limbs of Branchipus or __; Apus, the correspond ences of the two are striking.

  • An erroneous view of the fundamental morphology of the Crustacean limb, and consequently of that of other Arthropoda, came into favour owing to the acceptance of the highly modified limbs of Astacus as typical.

  • The range of modification of which the rami or limb-branches of the limbs of Arthropoda are capable is very large, and in allied orders or even families or genera we often find d z what is certainly the palp of the same appendage (as determined by numerical position of the segments) - in one case antenniform, in another chelate, in another pediform, and in another reduced to a mere stump or absent altogether.

  • 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.

  • This is the usual uni-ramose limb found in the various classes of Arthropoda.

  • e n / e n 2' (the eye-stalk and sessile lateral eyes of Arthropoda generally, exclusive of Peripatus).

  • It may be pointed out that the most radical difference presented in this list is that between appendages consisting of the corm alone without rami (Onychophora) and those with more or less developed rami (the rest of the Arthropoda).

  • There is no reason to suppose that any of the forms of limb observed in Arthropoda may not have been independently developed in two or more separate diverging lines of descent.

  • 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.

  • Therefore, it seems to be, with our present knowledge, a hopeless task to analyse the branchial organs of Arthropoda and to identify them genetically in groups.

  • A brief notice must suffice of the structure and history of the Eyes, the Tracheae and the so-called Malpighian tubes of Arthropoda, though special importance attaches to each in regard to the determination of the affinities of the various animals included in this great sub-phylum.

  • We are also, by the isolation of Peripatus and the impossibility of tracing to it all other tracheate Arthropoda, or of regarding it as a degenerate offset from some one of the tracheate classes, forced to the conclusion that the tracheae of the Onychophora have been independently acquired.

  • It is a noteworthy fact that other tubes in these same terrestrial Arthropoda - namely, the ducts of glands - are similarly strengthened by a chitinous cuticle, and that a spiral or annular thickening of the cuticle is developed in them also.

  • It seems that we have to suppose that the vasifactive tissue of Arthropoda can readily take the form of air-holding instead of blood-holding tubes, and that this somewhat startling change in its character has taken place independently in several instances - viz.

  • Tubes of renal excretory function in a like position occur in most terrestrial Arthropoda - viz.

  • We shall now pass the groups of the Arthropoda in review, attempting to characterize them in such a way as will indicate their probable affinities and genetic history.

  • SUB-Phylum Arthropoda.

  • 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.

  • In the other classes of Arthropoda we have more or less complete embryological evidence on the subject.

  • When the facile tendency of Arthropoda to develop tracheal air-tubes is admitted, it becomes probable that the tracheae of Hexapods do not all belong to one original system, but may be accounted for by new developments within the group. Whether the primitive tracheal system of Hexapoda was a closed one or open by serial stigmata in every somite remains at present doubtful, but the intimate relation of the system to the wings and tracheal gills cannot be overlooked.

  • 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.

  • We may tabulate the facts as to head-structure in Chaetopoda and Arthropoda as follows: Grade x (below the Arthropoda).

  • Grade' (of the Arthropoda).

  • Grade 2 (of the Arthropoda).

  • Grade 3 (of the Arthropoda).

  • Grade 4 (of the Arthropoda).

  • We are prohibited by a general consideration of metamerism in the Arthropoda from adopting the hypothesis of intercalation of somites.

  • The solid palpless mandible such as we now see in some Arthropoda is, necessarily, a late specialization.

  • - References to the early literature concerning the group Arthropoda will he found in Carus, Geschichte der Zoologie.

  • Detailed references will be found under the articles on the separate groups of Arthropoda.

  • PERIPATUS, a genus of animals belonging to the air-breathing division of the phylum Arthropoda.

  • It differs, however, from all other Arthropoda in such important respects that a special class, equivalent in rank to the old-established Arthropod classes, had been created for its sole occupancy.

  • As in all Arthropoda, the perivisceral cavity is a haemocoele, i.e.

  • Its true place in the system, as a primitive member of the group Arthropoda, was first established in 1874 by H.

  • Finally, the tracheae, though not characteristic of all the classes of the Arthropoda, are found nowhere outside that group, and constitute a very important additional reason for uniting Peripatus with it.

  • Crustaceans The largest Phylum of invertebrate animals is the Arthropoda containing the crustaceans The largest Phylum of invertebrate animals is the Arthropoda containing the crustaceans with over 50,000 marine species.

  • The body consists of a number of exactly similar or closely similar segments, which are never fused and metamorphosed, as in the Arthropoda, to form specialized regions of the body.

  • Where locomotive appendages (the parapodia of the Polychaeta) exist, they are never jointed, as always in the Arthropoda; nor are they modified anteriorly to form jaws, as in that group.

  • These muscles are not striated, as they are in the Arthropoda.

  • Thus in the Chaetopoda the perivisceral cavity is coelomic; in this respect the group contrasts with the Arthropoda and Molluscs, where the perivisceral cavity is, mainly at least, part of the vascular or haemal system, and agrees with the Vertebrata.

  • The plan of the central nervous system is therefore that of the Arthropoda.

  • The cerebral ganglia constitute an archicerebrum for the most part, there being no evidence that, as in the Arthropoda, a movement forward of post-oral ganglia has taken place.

  • HEXAPODA (Gr., six, and g obs, foot), a term used in systematic zoology for that class of the Arthropoda, popularly known as insects.

  • von Siebold's (1848) name of Arthropoda.

  • And the wings, though not always present, are highly characteristic of the Hexapoda, since no other group of the Arthropoda has acquired the power of flight.

  • In all main points of their internal structure the Hexapoda agree with other Arthropoda.

  • The nature of these organs is described in the article Arthropoda.

  • r remarkable type of bloodsystem characterizing the Arthropoda.

  • Lecaillon (1898) on various leaf beetles, tend to show that the organ " in the embryos of the lower Arthropoda corresponds with whole of the " mid-gut " arises from the proliferation of cells at the the region invaginated to form the serosa of the hexapod embryo.

  • 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.

  • Relationships And Phylogeny The Hexapoda form a very clearly defined class of the Arthropoda, and many recent writers have suggested that they must have arisen independently of other Arthropods from annelid worms, and that the Arthropoda must, therefore, be regarded as an " unnatural," polyphyletic assemblage.

  • The cogent arguments against this view are set forth in the article on Arthropoda.

  • of the animals included in the class Hexapoda of the great phylum (or sub-phylum) Arthropoda.

  • In 1735 appeared the first edition of the Systema naturae of Linnaeus, in which the "Insecta" form a group equivalent to the Arthropoda of modern zoologists, and are divided into seven orders, whose names - Coleoptera, Diptera, Lepidoptera, &c., founded on the nature of the wings - have become firmly established.

  • The Insecta of Linnaeus was a group exactly equivalent to the Arthropoda founded a hundred years later by Siebold and Stannius.

  • The position of the Arachnida in the great sub-phylum Arthropoda, according to recent anatomical and embryological researches, is explained in the article Arthropoda.

  • - Modern views as to the classification and affinities of the Arachnida have been determined by the demonstration that Limulus and the extinct Eurypterines (Pterygotus, &c.) are Arachnida; that is to say, are identical in the structure and relation of so many important parts with Scorpio, whilst differing in those respects from other Arthropoda, that it is impossible to suppose that the identity is due to homoplasy or convergence, and the conclusion must be accepted that the resemblances arise from close genetic relationship. The view that Limulus, the king-crab, is an Arachnid was maintained as long ago as 182 9 by Strauss-Diirckheim (1), on the ground of its possession of an internal cartilaginous sternum - also possessed by the Arachnida (see figs.

  • But it is necessary to remember, in the light of recent discoveries, that the sixth prosomatic pair of appendages is carried on the seventh somite of the whole series, there being two prosthomeres or somites in front of the mouth, the first carrying the eyes, the second the chelicerae; also that the first mesosomatic or genital somite is not the seventh or even the eighth of the whole series of somites which have been historically present, 1 See the article Arthropoda for the use of the term " prosthomere."

  • - It appears (see Arthropoda) that there is embryological evidence of the existence of two somites in Arachnida which were originally post-oral, but have become prae-oral by adaptational shifting of the oral aperture.

  • 12 in the article Arthropoda.

  • The genital ducts of Arthropoda are, like the green glands, shell glands and coxal glands, to be regarded as coelomoducts (gonocoels).

  • We know that such a lateral position of the nerve cords preceded the median position in both Arthropoda and Chaetopoda.

  • It seems that there is a primitive tendency in the Arthropoda for the arteries to accompany the nerve cords, and a " supra-spinal " artery - that is to say, an artery in close relation to the ventral nerve cords--has been described in several cases.

  • It is very probable that in Scorpio they do not serve merely to secrete a digestive fluid (shown in other Arthropoda to resemble the pancreatic fluid), but that they also become distended by the juices of the prey sucked in by the scorpion - as certainly must occur in the case of the simple unbranched gastric caeca of the spiders.

  • In Limulus Lankester found (15) the spermatozoa to possess active flagelliform " tails," and to resemble very closely those of Scorpio which, as are those of most terrestrial Arthropoda, are actively motile.

  • We have now passed in review the principal structural features in which Limulus agrees with Scorpio and differs from other Arthropoda.

  • (From Lankester, loc. cit., after Packard.) with all air-breathing Arthropoda except Peripatus, possesses these tubules, which are often called Malpighian tubes.

  • In fact it is not possible to maintain that the renal excretory tubes of the gut are of one common origin in the Arthropoda.

  • 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.

  • Further, it is pointed out by Korschelt and Heider that the hinder portion of the gut frequently acts in Arthropoda as an organ of nitrogenous excretion in the absence of any special excretory tubules, and that the production of such caeca from its surface in separate lines of descent does not involve any elaborate or unlikely process of growth.

  • When we consider the relationships of the various classes of Arthropoda, having accepted and established the fact of the close genetic affinity of Limulus and Scorpio, we are led to important conclusions.

  • It has been insisted, by those who accepted Lankester's original doctrine of the direct or genetic affinity of the Chaetopoda and Arthropoda, that Apus and Branchipus really come very near to the ancestral forms which connected those two great branches of Appendiculate (Parapodiate) animals.

  • 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.

  • (From Korschelt and Heider.) quently take place (as in all Arthropoda) at the posterior extremity of the body, whilst excalation of somites may occur at the constricted areas which often separate adjacent " regions," though there are very few instances in which it has been recognized.

  • Claus, " Degeneration of the Acari and Classification of Arthropoda," Anzeiger d.

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

  • the Rotifera, the Chaetopoda and the Arthropoda.

  • Sub-phyla: Rotifera, Chaetopoda, Arthropoda.

  • Arthropoda (q.v.).

  • (See ARTHROPODA.)

  • Annelids are segmented worms, and differ from the Arthropoda, which they closely resemble in many respects, by the possession of a portion of the coelom traversed by the alimentary canal.

  • Yet in the next family Alonella nana (Baird) disputes the palm and claims to be the smallest of all known Arthropoda.

  • 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.

  • 21), so that its fibres join the anterior faces of the nerve-end cells as in Vertebrates, instead of their posterior faces as in the cephalic eyes of Mollusca and Arthropoda; moreover, the lens is not a cuticular product but a cellular structure, which, again, is a feature of agreement with the Vertebrate FIG.

  • The perioesophageal nerve-ring of Chaetopoda and Arthropoda is represented, not by the collar first mentioned in the above description, but by the commissures connecting the cerebral and pedal ganglia.

  • (1875); " Note on the Coelom and Vascular System of Mollusca and Arthropoda," Quart.

  • Experiments to test distastefulness have also been made with various kinds of insectivorous Arthropoda, like spiders and mantises.

  • Among the remaining divisions of Invertebrata special mention may be made of the air-breathing Arthropoda - on the whole the most important and interesting group. About one-third of the animals belonging thereto that occur in the higher regions are exclusively alpine (or alpine and northern); these characteristically alpine forms being furnished chiefly by the spiders, beetles and butterflies.

  • The animals thus associated, the Rotifera, Chaetopoda and Arthropoda, are composed of a larger or smaller number of hollow rings, each ring possessing typically a pair of hollow lateral appendages, moved by intrinsic muscles and penetrated by blood-spaces.

  • Arthropoda are very abundant and as yet little known.

  • Collectively, they are ranked as one of the classes forming the sub-phylum Arthropoda, and their distinguishing characters are discussed under that heading.

  • It will be sufficient here to define them as Arthropoda for the most part of aquatic habits, having typically two pairs of antenniform appendages in front of the mouth and at least three pairs of post-oral limbs acting as jaws.

  • - As in all Arthropoda the body consists of a series of segments or somites which may be free or more or less coalesced together.

  • This is especially the case in the anterior part of the body, where, in correlation with the " adaptational shifting of the oral aperture " (see Arthropoda), a varying number of somites unite to form the "cephalon " or head.

  • As in all Arthropoda, it is composed of three divisions, a fore-gut or stomodaeum, ectodermal in origin and lined by an inturning of the chitinous cuticle, a mid-gut formed by endoderm and without a cuticular lining, and a hind-gut or proctodaeum, which, like the fore-gut, is ectodermal and is lined by cuticle.

  • 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.

  • There is every reason to believe 2, Gastric teeth of common that, in the primitive Arthropoda, lobster, Homarus vulgaris.

  • A very remarkable condition of the blood-system, unique, as far as is yet known among the Arthropoda, is found in a few genera of parasitic Copepoda (Lernanthropus, Mytilicola).

  • 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.

  • The central nervous system is constructed on the same general plan as in the other Arthropoda, consisting of a supra-oesophageal ganglionic mass or brain, united by circumoesophageal connectives with a double ventral chain of segmentally arranged ganglia.

  • The compound eyes are very similar in the details of their structure (see Arthropoda) to those of insects (Hexapoda).

  • As in Arthropoda, the hairs or setae on the surface of the body are important organs of sense and are variously modified for special sensory functions.

  • The gonads, as in other Arthropoda, are hollow saccular organs, the cavity communicating with the efferent ducts.

  • The definition just quoted might include all animals belonging to the groups of the Arthropoda and Annelida, and U.

  • The class Insecta of Linnaeus (1758) was coextensive with the Arthropoda of modern zoologists.

  • For a general account of the structure, development and relationships of insects, see Arthropoda and Hexapoda, while details of the form, habits and classification of insects will be found in articles on the various orders or groups of orders (Aptera, Coleoptera, Dipteria,Hemiptera,Hymenoptera,Lepidoptera,Neuroptera, Orthoptera, Thysanoptera), and in special articles on the more familiar divisions (ANT, BEE, Dragon-Fly, Earwig, &c.).

  • GNATHOPODA, a term in zoological classification, suggested as an alternative name for the group Arthropoda.

  • ARTHROPODA, a name, denoting the possession by certain animals of jointed limbs, now applied to one of the three sub-phyla into which one of the great phyla (or primary branches) of coelomocoelous animals - the Appendiculata - is divided; the other two being respectively the Chaetopoda and the Rotifera.

  • The word "Arthropoda " was first used in classification by Siebold and Stannius (Lehrbuch der vergleich.

  • We have, in fact, returned very nearly to Cuvier's conception of a great division or branch, which he called Articulata, including the Arthropoda and the Chaetopoda (Annelides of Lamarck, a name adopted by Cuvier), and differing from it only by the inclusion of the Rotif era.

  • The 1 The group Arthropoda itself,th usconstituted,wasprecisely identical in its area with the Insecta of Linnaeus, the Entoma of Aristotle.

  • Hence the term Appendiculata was introduced by Lankester (preface to the English edition of Gegenbaur's Comparative Anatomy, 1878) to indicate the group. The relationships of the Arthropoda thus stated are shown in the subjoined table: - (Sub-phylum r.

  • (See, however, 8.) The Arthropoda might be better called the " Gnathopoda," since their distinctive character is, that one or more pairs of appendages behind the mouth are densely chitinized and turned (fellow to fellow on opposite sides) towards one another so as to act as jaws.

  • There are other remarkable and distinctive features of structure which hold the Arthropoda together, and render it impossible to conceive of them as having a polyphyletic origin, that is to say, as having originated separately by two or three distinct lines of descent from lower animals; and, on the contrary, establish the view that they have been developed from a single line of primitive Gnathopods which arose by modification of parapodiate annulate worms not very unlike some of the existing Chaetopods.

  • These additional features are the following - (1) All existing Arthropoda have an ostiate heart and have undergone " phleboedesis," that is to say, the peripheral portions of the blood-vascular system are not fine tubes as they are in the Chaetopoda and as they were in the hypothetical ancestors of Arthropoda, but are swollen so as to obliterate to a large extent the coelom, whilst the separate veins entering the dorsal vessel or heart have coalesced, leaving valvate ostia (see fig.

  • (2) In all existing Arthropoda the region in front of the mouth is no longer formed by the primitive prostomium or head-lobe, but one or more segments, originally post-oral, with their appendages have passed in front of the mouth (prosthomeres).

  • Tabular Statement of the Grades, Classes and Sub-classes of the Arthropoda.

  • - It will be convenient now to give in the clearest form a statement of the larger subdivisions of the Arthropoda which it seems necessary to recognize at the present day.

  • SUB-Phylum Arthropoda (of the Phylum Appendiculata).

  • Hyparthropoda (hypothetical forms connecting ancestors of Chaetopoda with those of Arthropoda).

  • The body of the Arthropoda is more or less clearly divided into a series of rings, segments, or somites which can be shown to be repetitions one of another, possessing identical parts and organs which may be larger or smaller, modified in shape or altogether suppressed in one somite as compared with another.

  • The Arthropoda are all distinguished from, The prostomial the Chaetopoda by the fact that the head A ganglion-mass or consists of one or more somites which lie in archi cerebrum.

  • It was conceived by Huxley, among others, that the same number of cephalic somites would be found to be characteristic of all the diverse classes of Arthropoda, and that the somites, not only of the head but of the various regions of the body, could be closely compared in their numerical sequence in classes so distinct as the Hexapods, Crustaceans and Arachnids.

  • that all the Arthropoda are to be traced to a common ancestor resembling a Chaetopod worm, but differing from it in having lost its chaetae and in having a prosthomere in front of the mouth (instead of prostomium only) and a pair of hemignaths (mandibles) on the parapodia of the buccal somite.

  • It has taken some time to obtain any general acceptance of the view that the parapodia of the Chaetopoda and the limbs of Arthropoda are genetically identi cal structures; yet if we compare the para podium of Tomopteris or of Phyllodoce with one of the foliaceous limbs of Branchipus or __; Apus, the correspond ences of the two are striking.

  • An erroneous view of the fundamental morphology of the Crustacean limb, and consequently of that of other Arthropoda, came into favour owing to the acceptance of the highly modified limbs of Astacus as typical.

  • The range of modification of which the rami or limb-branches of the limbs of Arthropoda are capable is very large, and in allied orders or even families or genera we often find d z what is certainly the palp of the same appendage (as determined by numerical position of the segments) - in one case antenniform, in another chelate, in another pediform, and in another reduced to a mere stump or absent altogether.

  • 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.

  • This is the usual uni-ramose limb found in the various classes of Arthropoda.

  • e n / e n 2' (the eye-stalk and sessile lateral eyes of Arthropoda generally, exclusive of Peripatus).

  • It may be pointed out that the most radical difference presented in this list is that between appendages consisting of the corm alone without rami (Onychophora) and those with more or less developed rami (the rest of the Arthropoda).

  • There is no reason to suppose that any of the forms of limb observed in Arthropoda may not have been independently developed in two or more separate diverging lines of descent.

  • 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.

  • Therefore, it seems to be, with our present knowledge, a hopeless task to analyse the branchial organs of Arthropoda and to identify them genetically in groups.

  • A brief notice must suffice of the structure and history of the Eyes, the Tracheae and the so-called Malpighian tubes of Arthropoda, though special importance attaches to each in regard to the determination of the affinities of the various animals included in this great sub-phylum.

  • We are also, by the isolation of Peripatus and the impossibility of tracing to it all other tracheate Arthropoda, or of regarding it as a degenerate offset from some one of the tracheate classes, forced to the conclusion that the tracheae of the Onychophora have been independently acquired.

  • It is a noteworthy fact that other tubes in these same terrestrial Arthropoda - namely, the ducts of glands - are similarly strengthened by a chitinous cuticle, and that a spiral or annular thickening of the cuticle is developed in them also.

  • It seems that we have to suppose that the vasifactive tissue of Arthropoda can readily take the form of air-holding instead of blood-holding tubes, and that this somewhat startling change in its character has taken place independently in several instances - viz.

  • Tubes of renal excretory function in a like position occur in most terrestrial Arthropoda - viz.

  • We shall now pass the groups of the Arthropoda in review, attempting to characterize them in such a way as will indicate their probable affinities and genetic history.

  • SUB-Phylum Arthropoda.

  • Eoperipatus, Peripatopsis, Opisthopatus, &c. (See Peripatus.) Grade C (of the Arthropoda).

  • 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.

  • In the other classes of Arthropoda we have more or less complete embryological evidence on the subject.

  • When the facile tendency of Arthropoda to develop tracheal air-tubes is admitted, it becomes probable that the tracheae of Hexapods do not all belong to one original system, but may be accounted for by new developments within the group. Whether the primitive tracheal system of Hexapoda was a closed one or open by serial stigmata in every somite remains at present doubtful, but the intimate relation of the system to the wings and tracheal gills cannot be overlooked.

  • 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.

  • We may tabulate the facts as to head-structure in Chaetopoda and Arthropoda as follows: Grade x (below the Arthropoda).

  • Grade' (of the Arthropoda).

  • Grade 2 (of the Arthropoda).

  • Grade 3 (of the Arthropoda).

  • Grade 4 (of the Arthropoda).

  • We are prohibited by a general consideration of metamerism in the Arthropoda from adopting the hypothesis of intercalation of somites.

  • The solid palpless mandible such as we now see in some Arthropoda is, necessarily, a late specialization.

  • - References to the early literature concerning the group Arthropoda will he found in Carus, Geschichte der Zoologie.

  • Detailed references will be found under the articles on the separate groups of Arthropoda.

  • PERIPATUS, a genus of animals belonging to the air-breathing division of the phylum Arthropoda.

  • It differs, however, from all other Arthropoda in such important respects that a special class, equivalent in rank to the old-established Arthropod classes, had been created for its sole occupancy.

  • This class has been named the Prototracheata or Onychophora (see Arthropoda), and may be most appropriately placed in the system in the neighbourhood of the Myriapoda, though it must not be forgotten that it differs from the Myriapoda more than the Myriapoda differ from other Arthropoda, and that in some respects it presents features which recall the segmented worms (Annelida).

  • As in all Arthropoda, the perivisceral cavity is a haemocoele, i.e.

  • Its true place in the system, as a primitive member of the group Arthropoda, was first established in 1874 by H.

  • Finally, the tracheae, though not characteristic of all the classes of the Arthropoda, are found nowhere outside that group, and constitute a very important additional reason for uniting Peripatus with it.

  • This unlikeness to other Arthropoda is mainly due to the Annelidan affinities which it presents, but in part to the presence of the following peculiar features: (I) the number and diffusion of the tracheal apertures; (2) the restriction of the jaws to a single pair; (3) the disposition of the generative organs; (4) the texture of the skin; and (,) the simplicity and similarity of all the segments of the body behind the head.

  • Arthropods are invertebrates belonging to the phylum Arthropoda, the jointed-leg, spineless creatures of the world.

  • Arthropoda include insects, arachnids (spiders), crustaceans, and other subgroups.

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