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UNITED STATES

EXPLORING EXPEDITION,

BY AUTHORITY OF CONGRESS.

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UNITED STATES

EXPLORING EXPEDITION.

DURING THE YEARS

1838, 1839, 1840, 1841, 1842.

UNDER THE COMMAND OF

CHARLES WILKES, U.8.N.

C E U STC E A,

BY

JAMES D. DANA, A.M.,

MEMBER OF THE SOC. C.KS. NAT. CUR. OF MOSCOW; THE SOC. PHILOMATHIQUE OF PARIS; THB

GEOLOGICAL SOCIETY OF LONDON; THE AMF.RICAN ACADEMY OF ARTS AND SCIENCES

AT BOSTON; THE ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA, ETC.

WITH A FOLIO ATLAS OF NINETY-SIX PLATES.

PART I.

PHILADELPHIA: PRINTED BY C. SHERMAN.

1852.

CRUSTACEA,

PART I.

TJITIVERSITY

CONTENTS.

INTRODUCTORY REMARKS, . .. > ; v'.; :. l

CLASSIFICATION OF CRUSTACEA, . . . . . . 3

HOMOLOGIES OF CRUSTACEA, ..... .19

CRUSTACEA PODOPHTHALMIA, . . . . . ." . 45

ORDER I. EUBRANCHIATA, . 45

TRIBE I. BRACHYURA, 68

I. MAIOIDEA, 75

I. MAIINEA, ....... 77

II. PARTHENOPINEA 186

II. CANCROIDEA, . 142

I. CANCRINEA, . . . . . .147

II. TELPHUSINEA, . . . . . 292

III. CYCLINEA, 294

III. CORYSTOIDEA, . 290

r

IV. GRAPSOIDEA, 306

V. LEUCOSOIDEA, 389

TRIBE II. ANOMOURA, . .398

I. DROMIDEA, . 402

II. BELLIDEA, . 403

III. RANINIDEA .403

IV. HIPPIDEA, 404

V. PORCELLANIDEA .410

VI. LITHODEA, . 426

CONTENTS.

MM

VII. jEGLEIDEA, . . . . .476

IX. GALATHEIDEA, ... .478

APPENDIX. MEGALOPIDEA, ..... 484

TRIBE III. MACROURA, . ' . .497

I. THALASSINIDEA 503

II. ASTACIDEA, . . 615

III. CARIDEA, . . V . . . . 528

IV. PEN-ffilDEA, 600

ORDER II. ANOMOBRANCHIATA 612

I. SQUILLOIDEA, 614

II. MYSIDEA, . . . . . . . . 635

iy

CRUSTACEA,

INTRODUCTORY REMARKS.

THE collections of Crustacea, which are the subject of the following Report, were made by the Exploring Expedition at all the various points visited in the course of the cruise, and through all the oceans traversed. The principal coasts which have contributed to the department are as follows :

1. Madeira,

2. Cape Verde,

3. Rio Janeiro,

4. Rio Negro, Northern Patagonia,

5. Nassau Bay, Tierra del Puego,

6. Valparaiso, Chili, 1. Callao, Peru,

8. San Francisco, California,

9. Coast of Oregon,

10. Sandwich Islands,

11. Paumotu Islands, Pacific,

12. Society Islands,

13. Samoan or Navigator Islands,

14. Tongatabu,

15. Feejee Islands,

16. New Zealand,

17. New South Wales,

18. Kingsmill Islands,

19. Wakes Island,

20. The Phillippines, Sooloo Sea, Singa-

pore, and Cape Town.

Our stay at these different places varied from twenty-four hours to four months ; and the extent of the collections they afforded is conse- quently as various as the time allowed for exploration. The waters of the Atlantic, Pacific, Antarctic, and Indian Oceans also added largely to the number of oceanic species.

The scientific world naturally demands results correspondent with the opportunities for investigation. As bearing on this point, the

1

2 CRUSTACEA.

author deems it incumbent to state that the Crustacea constituted one out of three extensive departments under his charge, Geology and Zoophytes, reports on which subjects are already published, having occupied a large share of his time and labours. Moreover, the unfor- tunate wreck of the Peacock on the Columbia bar sacrificed all the collections made through two seasons in the South Pacific, ranging over the ocean from the Paumotus to the Navigator Islands and also to the Kingsmill Group, and only a few dried Crustacea, not included in the packages lost, answer to a detailed catalogue numbering more than a thousand specimens.

Besides this misfortune, another befell the collections after reaching the country, before the return of the Expedition. A large part of the packages were unfortunately opened, and the specimens prepared, by drying, for exhibition. By this means, the references to the catalogues were to some extent lost, and many specimens were badly injured. Some were rendered wholly unfit for description, especially those of small size, which, without regard to their delicacy of structure, were taken from the bottles containing them and dried, and sometimes transfixed with pins, to the obliteration of many of their characters. Moreover, the larger species were rendered by this process unfit for dissection.

Notwithstanding these occurrences, the number of new species described in the following pages exceeds five hundred, although in many of those collected we have been anticipated by foreign inves- tigators, owing to the delay in our publications.

The species embraced belong to every branch of the department of Crustacea, including the minute Entomostraca as well as the higher grades. The subject of classification has therefore come necessarily under consideration. We have also been led for the same reason to a study of the homologies of Crustacea, and have endeavoured to present the parallel relations of species in all the prominent groups.

I. ON THE CLASSIFICATION OF CRUSTACEA.

THE following observations on the classification of Crustacea relate only to the grander divisions of this class of animals. The various subdivisions and their distinctions come under consideration in the succeeding descriptive part of the work, in connexion with the detailed descriptions of the several groups.

In presenting our remarks on this subject, we offer first a few ob- servations on the limits of the department of Crustacea, and a brief review of the distinctive characters of the class.

I. LIMITS OF THE DEPARTMENT OF CRUSTACEA, AND DISTINCTIVE CHARACTERS OF THE CLASS.

1. Limits. The only point of doubt that has existed of late upon the limits of the department of Crustacea refers to the lower orders of the class, and, through recent investigations, the uncertainties are now mostly removed. The Cirripedia have been claimed by the concho- logist as Mollusca, and the Rotifers by Ehrenberg and others as a branch of Infusoria. The former are so completely like Cypridinea in the young state, as first shown by Thompson,* both in external form and internal structure, and so unlike any species of Mollusca, that their relations to the Articulata were made out satisfactorily by this observation alone. The author collected some of these young Anatifse in the Equatorial Atlantic in 1838, and, not being aware at the time of Thompson's investigations, the species were referred to the Cypris group. Subsequent investigations off Fuegia, where the young and adult forms were found together, enabled him to trace out the transitions. Another fact of importance, fixing the relations of the Cirripeds, was observed by the author in the harbour of Rio Janeiro. Numerous exuviae of Cirripeds were collected, proving that these animals undergo exuviation, a process in growth characteristic

* Zoological Kesearches, by J. V. Thompson, Esq., F.L.S., No. 3, January, 1830.

4 CRUSTACEA.

of this branch of the Articulata, and not so of any true Mollusca. Again, the organs of the mouth as well as the jointed structure of the legs are completely Crustacean in type.

The Rotifers have the mandibles and other mouth-organs of Crus- tacea, and some of them resemble certain Entomostraca in general form, and in the jointed structure of the caudal extremity. In these species we have, therefore, the lowest Crustacean form under a Eadiate type, the type of the inferior branch of the animal kingdom.

Crustacea also pass, by almost imperceptible shades, into Vermes, through the Caligus and Lernsea tribes; the most degraded Lernaaan forms having the sluggishness and almost memberless character of the lowest worms. Their resemblance to the typical Crustacea is so slight, that, without a knowledge of the gradations through the well- modelled Caligi to the higher forms, their relations to the class would hardly be suspected.

2. Characteristics. On account of the wide variations among Crus- tacea, the systematist experiences great difficulty in laying down the characteristics of the class.

The higher divisions have a regular heart ; the lower (and this is true even of some Caligidse) have no heart, and only two or three valves in the course of the circulation.

The higher have a system of vessels for the arterial circulation, the venous system only being lacunal; the lower have no vessels for circulation in any part, and the blood sweeps along among the muscles in broad currents, flowing off in side channels wherever passages are open, more like the sap in the leaf of a plant than what is naturally looked for in the zoological kingdom.

The higher orders have branchiae for the aeration of the blood attached to the thoracic members ; species of another type have allied organs attached to the abdominal members; and those^of the lower orders are without any trace of branchiae or corresponding organs, and the function of aeration devolves upon the exterior surface of the body.

The higher orders have a nervous ganglion for each segment of the body, and these ganglia are clustered in two masses only when the limbs are gathered closely about a centre, with the abdomen small and inflexed against the thorax, as in Crabs ; but in the lower orders, although the body may consist of a series of segments, we find at times only one single ganglion, pierced by the oesophagus, and placed

CLASSIFICATION OF CRUSTACEA. 5

above the mouth, from which cords pass forward and backward, and subdivide, in order to supply the posterior segments and their members; and in this particular, the great characteristic which is laid down as dividing the Articulata from the Mollusca, fails of being distinctive, and we find essentially the nervous system of a molluscan with a crustacean structure.

The higher have large biliary glands ; the lower often no distinct glandular masses of this kind.

Again, as already observed, while in the higher orders the species have a series of limbs for locomotion and prehension, the members are reduced in the lowest to a single pair, or even this is wanting, a long head with its mouth fitted for suction, and a long tail, making up the body.

What is, then, a Crustacean ? No definition can be wholly satis- factory. As in other cases, the question must be answered by defining the essential characters of the typical form, and then the relations of the extreme divisions are to be distinguished by gradations of structure, rather than by complete conformity to the type. We observe, how- ever, that there are some invariable characters. All have a straight intestine, without convolutions; all pass through a series of meta- morphoses in development; all undergo exuviation; all have the head and thorax combined essentially in a single cephalothorax ; all are aquatic in their mode of respiration, the surface of certain gill-like organs, or of some or all parts of the body, serving in aeration.

While, therefore, Crustacea, in their typical forms, have the nervous system of other Articulata, and are thus widely removed from Mol- lusca, they graduate into species that have nearly the nervous system of the latter division. Yet the articulated body, the structure of the mouth, the jointed appendages, the character of the intestine, and the process of exuviation, are decisive characteristics, with few exceptions ; and in the exceptions, the species are elongated and resemble worms rather than Mollusca.

Again, while related to Insects in the nervous system, they are separated from them by the existence of branchiae, or, if branchiae are absent, by the fact that the surface of the body performs the function of aeration. In other words, while Crustacea are aquatic Articulata, Insects are essentially sub-aerial species. Moreover, the process of exuviation, the structure of the heart, the coalescence of the head and thorax, and the large number of jointed limbs in the typical forms,

2

(J CRUSTACEA.

besides other characters, distinguish Crustacea from Insecta. A close approximation of Crustacea to other Articulata is not to be expected, except with aquatic species. And we find an analogy with the aquatic larvae of many insects, and still closer with certain Vermes, as the Helminths, into which the lower grades, as they are more and. more nude of members, evidently pass. A strongly-drawn line is here not to be expected, since both are divisions of the same sub- kingdom, and both are fitted for the same element and similar modes of life.

The position of Crustacea in the scale of animals among the Articu- lata has been learnedly discussed by Professor Agassiz ;* and he has shown, we think satisfactorily, that they should rank below Insects, and above Worms. The gradation into Worms is evidence on the latter point, and the analogy to the aquatic larves of Insects on the former. This author remarks upon the greater number of limbs in Crustacea, which is also a peculiarity commonly of the imperfect insect or larve, the smaller number in the mature insect being a result of a higher stage of development. He also observes that the separation of the head and thorax is further indication that Insects rank highest. It is true that Crustacea attain a size never found among the Insecta. But this is attributable to their living in a denser element, and is analogous to the occurrence of the largest but lowest of Mammalia in the ocean. Moreover, size of body is no necessary criterion of relative rank, for, unless the nervous system is of a higher grade as the size increases, the bulk is so far only an encumbrance to the weak forces within, and less agility of motion and inferior attributes in other respects are the consequence. Thus the huge medusa is but an unwieldy mass compared with minute acalephs, and the large crab but a clumsy animal alongside of the nimble ant.

It seems to be a correct principle laid down by Professor Agassiz, that in each zoological group the aquatic species are inferior in grade to those of the land.

II. SUBDIVISIONS OF CRUSTACEA.

In the classification of Crustacea, we adopt mainly the grand divi- sions laid down in the excellent treatise by Milne Edwards, although

* Classification of Insects from Embryological Data. By Prof. Agassiz. 28 pp. 4to., and one plate. Smithsonian Contrib. to Knowledge, vol. ii., art. 6.

CLASSIFICATION OF CRUSTACEA. 7

with some modifications as to the relative importance of these divisions, and the mode of grouping. The species with pedunculate eyes are naturally separated from those with sessile eyes ; and, in subdividing the latter, the large group including the Amphipoda and Isopoda are as properly separated from the other species, or Entomostraca. These steps in classification were first recognised essentially by the Swedish naturalist, Linnaeus.

The Cirripeds also have sessile eyes in the young, if not in the adult, state, and might be arranged with the second of the divisions mentioned. Yet they have so many peculiarities of structure, and their habits are so different from those of other Crustacea, that they more properly form a third grand division. Though Entomostracan in the young state, they subsequently develope in a widely divergent line, producing species with a persistent shelly covering not liable to be thrown off like the skin of the rest of the body, and having a fixed instead of a migratory body, with many peculiarities of structure.

The three grand groups among Crustacea are then as follows :

I. CRUSTACEA PODOPHTHALMIA.

II. CRUSTACEA EDRIOPHTHALMIA.

III. CRUSTACEA CIRRIPEDIA.

I. PODOPHTHALMIA. The Podophthalmia have a great similarity of structure, although exceedingly diverse in form, a diversity princi- pally owing to the greater or less development of the abdomen. The large carapax covering the thorax, exposing only two or three pos- terior segments, if any, and the characters of the cephalic organs and mouth, are very uniform features for the species. A variation takes place in the number of buccal appendages, but this consists simply in the posterior pairs being either appropriated exclusively to the mouth, or being so elongated as to act the part of feet.

There are species, however, which are removed from the rest by characters of high importance; yet such species are only examples of inferior development; that is, they are analogous in general character to the condition which the typical species present before arriving at complete maturity. Their degradation is seen in their having the thoracic branchiae exposed, instead of covered by the carapax ; and, in a lower stage, in having no thoracic branchiae, but only similar appendages to the abdomen ; and, in a stage still lower, in the branchiae being wanting altogether, and even the abdominal appen- dages rudimentary, as well as one, two, or three posterior pairs of tho-

8 CRUSTACEA.

racic feet ; a condition closely analogous to that of the Cyclopacea and other species among the Edriophthalmia, in which the same thoracic feet are wanting, as well as the abdominal feet, and also the branchiae. Thus it is that the Podophthalmia naturally include two groups, a higher, with the branchiae enclosed in the normal condition beneath the carapax, and a second, or lower, with the branchiae exposed, or wanting. These subdivisions of the Podophthalmia are :

Order I. EUBRANCHIATA or DEC APOD A.

Order II. ANOMOBRANCHIATA.

Eubranchiata. The Eubranchiates or Decapoda are naturally divided by Milne Edwards into the three groups *

Tribe I. BRACHYURA.

Tribe II. ANOMOURA.

Tribe III. MACROURA.

The nature and propriety of this arrangement will be the subject of extended remark on a future page, where the Eubranchiata come under consideration.

Anomobranchiata. In the Anomobranchiates the feet are in part two-branched or bifid, and this is an additional mark of their relation to immature forms. But this character is not universal ; and, more- over, it is presented by some species of the first division. We there- fore have not used the term Schizopoda for the group, but give it to a subdivision of the group which is characterized eminently by two- branched feet ; while another small subdivision or tribe, closely allied in most particulars, but with simple feet (Genus Lucifer), forms the tribe Aploopoda* Another portion of these species have the anterior thoracic feet clustered about the mouth, and cheliform, and this cha- racter suggested to Latreille the name Stomapoda (more properly Stomatopoda). This structure has a resemblance to that found in some Macroura, especially the Thalassinidea, and is a proper charac- teristic for one of the subdivisions of the Anomobranchiata.

The Anomobranchiata will thus include three tribes :

Tribe I. STOMAPODA.

Tribe II. SCHIZOPODA.

Tribe III. APLOOPODA.

II. EDRIOPHTHALMIA. The Edriophthalmia embrace a great variety of forms and structures, with very unlike habits. Separating the Amphi-

* From ocrXoos, simple or undivided, and tfouj, foot.

CLASSIFICATION OF CRUSTACEA. 9

pods and Isopods, it leaves a large group, ranging from well-organized forms to the sluggish worm-like Lernaea on one side, and to the microscopic Rotifer on the other, the line of gradation to the former being through the Caligacea, and to the latter through the Cyclops and Daphnia groups. Moreover, while some species have mouths with regular jaws, like the higher Crustacea, others have a trunk for suction ; and in still others (Limuli) the jaws are but the basal joints of the legs.

May we, in view of these differences, retain all the species in a common group, subdivided in accordance with the varieties of struc- ture ? or shall we, as done by Milne Edwards, give the very highest rank in classification to the character of the mouth, and so make our first three grand divisions of Crustacea paramount to all others, the following, 1, those with proper jaws (Crustace"s Maxille's) ; 2, sucking species (Crustace's S^eurs) ; 3, those with the basal joints of the legs acting as feet ?

The differences here alluded to, are, in our estimation, of compara- tively small importance. They are confined to the mouth, and are simply an adaptation of the same organs to somewhat different modes of life. The sucking Crustacea have the mandibles of other species, although more slender and placed in an elongate trunk ; and all other important characters are identical with those of certain maxil- lated species of like form and grade of structure.

In all Crustacea, the mandible is but a process from the basal joint of a leg, and the maxillae are of like character. In the higher species, the leg or jointed portion of the organ is short; but among the lower, it often has a large development, and all the maxillae may be like feet in form, and actually so in part of their functions. It is, therefore, but a single step, a shade beyond, which brings us to the Limuli, in which all the mouth organs are feet, and similar in form, the basal joints of which act together as jaws. In the Calani and Cypridinae, true mandibulated species, the maxillae are much enlarged, and the mandibles have long, jointed, fooWike appen- dages. Facts of this kind are too well known to require repetition, and they need but be appreciated, we think, to make the impropriety evident of laying that stress upon this characteristic which is done in the classification just alluded to.

We acknowledge that if this adaptation to suction occurred among the superior grades of Crustacea, it should have a high value in classi-

3

IQ CRUSTACEA.

fication ; but in fact it is confined to the lower grades, and it indicates only subordinate divisions of the inferior group. "We deem it of so little taxonomic importance, that we do not assume it as a basis of a grand distinction among the Edriophthalmia ; for it appears evident that the characters of the Amphipoda and Isopoda separate them widely from the rest of the species. Indeed, the sucking Caligi are so like the Sapphirinae among the Cyclopacea in every point of struc- ture, except the mouth, and so close even in this organ, that they seem to be only related groups of the same subdivision that of the Ento- mostraca.

Besides the species alluded to, there are also in this sub-class the Trilobita and Rotifera. The latter evidently have the lowest place. The former have been arranged both with the Entomostraca and Iso- poda; but the opinion of most authors places them at present in an intermediate group. A few brief considerations on this point are offered on a following page, after our observations on the Entomo- straca. The subdivisions of the sub-class Edriophthalmia are, therefore, as follows :

Order I. CHOEISTOPODA (or Tetradecapoda), including the Amphi- poda and Isopoda.

Order II. TRILOBITA.

Order III. ENTOMOSTRACA.

Order IV. ROTIFERA.

I. CHORISTOPODA. The Choristopoda are so called from x*p«rTi>«i sepa- rate, and «•«»«, foot, alluding to the most striking peculiarity of these species, separating them both from the Macroura and the Entomo- straca, viz. : that the thorax consists of a series of segments exposed to view and corresponding each to a pair of thoracic feet, which feet are ambulatory or prehensile. This division of the body into distinct segments from the head to the abdomen has scarcely an exception. Yet sometimes one or two pairs of the feet are rudimentary or wanting, and one or two of the anterior segments of the thorax, adjoining the head, are obsolescent or concealed; and in a very rare case two seg- ments are coalescent.

Among the Choristopoda, there are two prominent groups, the Am- phipoda and Isopoda.

In one group, the Amphipoda, the abdomen is elongated, with flexi- ble articulations ; the three anterior pairs of appendages are natatory ; the three posterior pairs styliform; the branchial vesicles are attached to the thoracic legs at base.

CLASSIFICATION OF CRUSTACEA. H

In the other, the Isopoda, the abdomen is short, with the articula- tions admitting of little flexion ; four or five pairs of abdominal appen- dages are lamellar and branchial, and only the posterior pair styliform.

Such are the characteristics laid down respectively for these groups. But there is another character of high importance, which has not been alluded to by previous authors, corroborative of this arrangement of the species. In the Amphipoda, four pairs of the thoracic feet are directed forward, and three outward and backward: while in the Iso- poda three pairs are directed forward, and four backward; that is, the sets of legs are four anterior and three posterior in the Amphipoda ; three anterior and four posterior in the Isopoda.

A third subdivision of the Choristopoda was proposed by Latreille, under the name Loemipoda (or Loernodipoda) . The species included are characterized by having the abdomen nearly or quite rudimentary. In the more essential characters they are closely related to the Amphi- poda, rather than to the Isopoda, and are not properly intermediate, nor a new type alike distinct from both ; for they have the thoracic branchial vesicles of the Amphipoda, and the abdomen in species that have this part somewhat elongated, partakes of the Amphipod charac- ter. They are properly therefore Amphipoda, with certain parts obso- lescent. That this is a correct view of their relations is shown by the thoracic feet, the four anterior pairs being forward feet, as in the Am- phipods. This conclusion has been adopted by many Zoologists.

There are, however, true intermediate species between the Amphi- pods and Isopods, and if any third or intermediate group is admitted, these should be considered as constituting it. These species belong to the genera Tanais, Arcturus, Leachia, and others allied. Like the Amphipoda, they have the four anterior pairs of feet of the forward series, and the three posterior of the hinder ; but like the Isopoda, they have the abdomen very short, and composed of six very short joints, and only the last pair of members is styliform (instead of the three posterior pairs, as in normal Amphipoda), while the others are lamellar and branchial, as in Isopods.

We therefore recognise three groups or tribes of the Choristopods, as follows :

1. Amphipoda. Branchial vesicles thoracic; forward series of tho- racic feet eight in number.

2. Anisopoda. Branchial vesicles abdominal ; forward series of tho-

12 CRUSTACEA.

racic feet eight in number, and used like arms, the six posterior am- bulatory or affixing.

3. Isopoda. Branchial vesicles abdominal; forward series of thoracic feet six in number, and all ambulatory (except that one or two ante- rior pairs are sometimes prehensile).

The name Anisopoda, from the Greek *»/»•««, unequal, and ™f,foot, alludes to the unlike functions and size of the anterior and posterior feet; the six posterior feet serve as feet for affixing themselves and standing; while, the eight anterior are used like arms, and are stretched out in search of food. Unlike most Amphipods and Isopods, therefore, the two sets of thoracic feet are strikingly different in func- tion ; and from the latter, they differ in that only the six posterior feet are ambulatory, and these have the additional function of enabling the animal to hold on to objects with an erect body, while the anterior members are free to move in every direction.

II. ENTOMOSTRACA. The Entomostraca agree in a general degrada- tion of character (by which they differ from the Choristopods) , rather than in any similarity of form ; yet, there are strong points which unite them. Unlike the Choristopods, the thorax does not consist of a series of seven segments following the head, with as many pairs of ambulatory, or ambulatory and prehensile feet. The abdomen, more- over, is without a regular series of appendages, either natatory or branchial, a caudal pair being usually the only one present, though sometimes, one or two preceding pairs, of peculiar structure, exist connected with the egg-system. Of the thoracic members, the pos- terior two pairs are, with few exceptions, obsolete, and in these excep- tions they are natatory ; and the three to five pairs preceding, when present, are natatory, excepting when one of them is genital in its use. These natatory feet are well seen in the groups, Cyclops, Sap- phirina, Caligus, Daphnia, and others ; and they are not found in the Cypris group, because three of these pairs of legs, elsewhere natatory, are here obsolete. These are striking peculiarities, removing the species far from the Choristopods; and they as closely bind the species together into a common family. Other points of resemblance are as follows : 1, the absence in general of arterial vessels ; 2, the frequent diversion of the posterior antennas to a natatory or prehensile purpose ; 3, the diverse forms often presented by the anterior thoracic members ; 4, the reduction of the nervous system, in most cases to a single ganglion, encircling the oesophagus, which gives out all the

CLASSIFICATION OF CRUSTACEA. ^3

nerves of the body without other ganglions in their course ; 5, the absence of branchiae, or any organs especially fitted for the purpose, in most species, and in cases where branchia-like appendages exist, they being only an adaptation to this function of some portion of a tho- racic leg.

The species differ among themselves in number of segments, which in a few instances is largely multiplied, and in others, reduced to four or five, or even less ; in the size of the anterior shell or carapax, which may be confined to the head, or be so enlarged as to enclose like a shell, the whole body; in the number of legs, which varies between a single pair, or even none, and fifty pairs or more ; in the number of organs devoted to the mouth, from a single pair of mandi- bles to mandibles with three pairs of maxillae or maxillipeds which may either be regular jaws, as in the higher Crustacea; or, may be imbedded, the basal joints of a series of legs acting as jaws; or, may project and form a moveable trunk, with slender, spiculiform organs for mandibles.

Of these differences, the last mentioned is of the widest importance. The trunk-form or sucker mouth characterizes a large number of species, which constitute a natural group, among the Entoraostraca ; and through these species, the class of Crustacea declines into the more degraded class of worms.

The mouth with jaws formed by the bases of a series of pairs of legs, affords a less important distinction. The aspect and structure in such species are peculiar, as observed in the Limuli, where this kiud of mouth is in perfection ; but, the mandibles are as much a pair of legs in the Cypris, and, indeed, they are the largest and strongest pair in these species ; moreover, in the Cyclops, the jointed or pediforrn por- tion of the mandibles and maxillae is largely developed, as already remarked. The Limuli are, therefore, but an example of the same principle, more perfectly carried out. Still, this may be a sufficient ground for placing these species in a separate subdivision of the Entoraostraca, although not authorizing a wide separation from the Order.

The Entomostraca are, therefore, distributed here into three groups, as follows :

Sub-order I. GNATHOSTOMATA (from v>ato<, jaw, and <rreu.», moutli). The mouth with regular jaws, and not forming a moveable trunk.

4

14 CRUSTACEA.

Sub-order II. CORMOSTOMATA (from x<.?/«««, trunk, and or^a). The mouth having the form of a moveable trunk.

Sub-order III. MEROSTOMATA (from /*„,..«, thigh, and «•«,*«). The basal joints of the legs constituting the joints.

Gnathostomata. Among the Gnathostomata there are species with an excessive or abnormal number of segments to the body, and lamellar appendages below, corresponding to the segments. These are naturally separated from the other species, which are essentially normal in their characters, the variations in the normal species being occasioned by obsolescence of parts, and not by increase. The former are very appropriately called PHYLLOPODA* by Latreille, in allusion to the foliaceous character and great number of the appendages, while the latter he designated LoPiiYROPODA,f on account of the fact that the feet are usually setigerous, being terminated or margined by long hairs.

The two groups include to some extent parallel forms, and admit of parallel subdivisions. Cyclops or Sapphirina of the Lophyropoda is analogous to Apus, among the Phyllopoda, and Cypris or Daphnia to Limnadia.

Moreover, these Phyllopodous species seem, in a certain degree, to be recent representatives of ancient forms, the Trilobites, which were also abnormal in the number of segments by a like multiplication. The Guathostomata are therefore naturally divided into these two groups, the Phyllopoda and Lophyropoda.

The LOPHYROPODA contain the natural groups or tribes Cyclopacea,, Daphniacea, and Oypridacea, as usually laid down ; and the Phyllo- poda, the Tribes Branchipodacea, Apodacea, and Limnadiacea. The graduation of the Macroura into the maxillated Entomostraca is seen through Mysis, Nebalia, and Branchipus, as observed by Milne Edwards, all three having pedunculate eyes.

The Cormostomata, or sucker-mouthed species, pertain to two widely different types one, the Cyclops type, as seen in Caligm (which has closely the form of Sapphirina, one of the genera of the Cyclops group), which group is named Pxcilopoda by Latreille ; and anotJier, the Arachnoid type, as in Nymphon, Pycnogonum, and the allied. The former pass into the Lernea group ; the latter are like spiders in form,

* From 0«AA»», leaf, and Tov<,foot.

f From A»0tip»5, having hairy or tail-like appendages, and irov(,foot.

CLASSIFICATION OF CRUSTA

and have their closest analogy among Crustacea with the Choristopods, especially the Caprellidae, the joints of the body being distinct, and the legs long and ambulatory.

Trilobites. With regard to the position of Trilobites in an arrange- ment of Crustacea, we offer the following observations.

In Apus and Limnadia we have examples of species with an abnor- mal number of segments, and foliaceous organs of locomotion concealed below. The absence of pediform jointed appendages among all exam- ples of fossil Trilobites is proof that there were no such appendages when living, as they could not have escaped preservation. A shell of a texture durable enough to be preserved, must have existed on legs suffi- ciently large to correspond in size with many Trilobites; for the articu- lation in all Crustacea legs is made by processes in the shelly covering of the legs, these being the only firm parts ; and such articulations for large legs would require a firm exterior, or else the member would be little better than a flabby piece of flesh, even if it had articulations. It is clear, therefore, that the organs of locomotion must have been folia- ceous, as in Limnadia. Such organs would be sufficient for swimming, and would not interfere with the adhesion of the animal, Chiton-like, to any body at hand. The antennae in some species may have been elongated, jointed organs, as specimens have shown.

Considering these points as established, does it follow that the species were properly Entomostracans related to the Phyllopoda? One great distinction separating the Entomostraca and Choristopods between which groups the Trilobita are supposed by authors to lie consists in the existence of a regular series of organs below the abdo- men in the latter, and the absence of such organs in the former. Even in Limnadia and Branchipus, the abdomen has no such series of organs.* This part of the body in the Phyllopods is often very short, as in Limnadia, or narrow, as in Branchipus, while in many Tri- lobites, as the genus Isotelus, it is very broad and large, so large, in fact, that we can hardly refuse to believe that it was provided with leaflets below, either like those of the thorax, or more properly bran- chial in character. In many species there is no obvious line between the thoracic and abdominal joints, as is true of some Isopoda, while in

* The large posterior segment of the Liraulus, with which the caudal appendage is articulated, and which covers foliaecous appendages, appears to be cephalothoracic and not abdominal, and the so-called tail in the common species is, therefore, all that exists of the abdomen.

16 CRUSTACEA.

.

others the distinction is obvious. In either case we have reason to conclude, from the breadth and extent of this part of the body, that the abdomen must have had its regular series of appendages.

On this ground, we should conclude that the species are interme- diate between the Isopoda among the Choristopods, and the Phyllo- poda among Entomostracans, and properly fall into neither of these divisions, though ranking most nearly with the former in perfection of structure and general character..

The following is a Tabular View of the Classification of Crustacea, explained in the preceding pages.

CLASSIFICATION OF CRUSTACEA.

17

CRUSTACEA.

SUHCLASSIS I.

SUBCLASSIS II.

SDBCLASi-13 III.

PODOPHTHALMIA.

EDRIOPHTHALMIA.

CIHRIPEDIA.

OSBO I.

OHDO I.

CHOBISTOPODA.

EUBRANCHIATA,

or

DECAPODA.

Tribus 1. AMPHIPODA.

2. AMSOPODA.

3. ISOPODA.

Tribus 1. BRACHYURA.

2. ANOMOUKA.

:l. MACROURA.

OBDO II.

TRILOBITA.

OSDO III.

KNTOMOSTKACA.

SUBORDO I. SUBOKDO II.

SoiiOltDO III.

GNATHOSTOMATA. Legio I.

COKUOSTOMATA. Legio I.

MEROSTOMATA.

OBDO II.

PHYLLOPODA.

P<ECILOPOBA.

ANOMOBRANCHIATA.

Tr.l. Branchipodacea.

Tribus 1. Caligacea.

Tribus 1. Limulitcea.

2. Apodacea.

2. Lermeacea.

Tribua 1. STOMATOPODA.

3. Limnadiacea.

2. SCHIZOPODA.

3. APLOOPODA.

Legio II.

Legio II.

LOPHYROPODA.

AEACBNOPODA.

it

Tribus 1. Cyclopacea.

Tr. 1. Xymphonacea.

2. Dapbniacea.

3. Cypridacca.

ORDO IV.

ROTIFEKA.

II. HOMOLOGIES OF CRUSTACEA.

1. General Typical Structure of the Body. Notwithstanding the great diversity of forms among Crustacea, there is in general little difficulty in tracing out the typical structure through all its many modifications, and distinguishing the true relations of the parts, even in the most aberrant species.

Before entering on this subject, it is important that we should ex- plain what we understand to be the typical structure in Crustacea. The investigations of Audouin and Milne Edwards have supplied the science, we think, with correct knowledge on this point. According to Edwards, the body of a Crustacean consists normally of twenty-one seg- ments, fourteen belonging to the head and thorax, and seven to the abdomen. In some species, as the Choristopods, seven of the first fourteen pertain to the thorax, and seven to the mouth and anterior part of the body or head ; but as the mouth-organs may become legs, and the legs mouth-organs, by slight variations, this last-mentioned division is far from general. The segments are as follows :

f 1st segment, ophthalmic.

I. CEPHALOTHORAX. \ 2(* segment> lst antennary- , , < 3d segment, 2d antennary.

14 segments. Y J

1 4th segment, mandibular.

V^ 5th to 14th segments, maxillary and podal, ten pairs.

/" 15th to 19th segments, bearing abdominal feet or appen-

II. ABDOMEN. S dages^w pairs.

_ , ^ 20th segment, bearing caudal abdominal appendages,

J one pair.

^ 21st or caudal segment, without appendages.

The variations among species, as brought out by Audouin, depend on the modifications which the normal segments may undergo by en- largement, diminution, coalescence, or obsolescence, together with such

20

CRUSTACEA.

changes of form in the existing parts as may accompany either of these conditions.

The normal parts of the separate rings or segments in the Articu- lata should be in mind in tracing out the homological relations of species, that is, that each of these rings consists normally of eight parts or segments, two below, called sternal, two above, called dorsal, one either side of the sternal, called the episternal, and one either side of the dorsal, called epimeral.

A different typical structure has been recently suggested, according to which the parts are multiples of the number six, instead of serai. It is based on the supposition that the organ called* the posterior or lower lip by Edwards and others, is a true pair of maxillae, to be counted with the following organs. Admitting this as correct, the cephalothorax consists normally of fifteen segments ; the first three, organs of senses, the next twelve pertaining to the mouth and thorax, the last six of these twelve (the outer maxillipeds thus included) being properly thoracic, according to the hypothesis. The abdomen, accord- ing to this hypothesis, consists of six segments, bearing appendages, and a seventh, which is normally composed of three segments. This gives for the normal number of segments twenty-four, a multiple of three or six.

As the truth of this hypothesis is to be ascertained mainly by in- quiring whether the so-called lower lip corresponds to a pair of maxillas or not, we offer a few considerations on this point. The organ consists of two oblong flat lobes, in some Decapods, somewhat maxilla-like in form. We observe, in the first place, that it is peculiar in being with- out articulations, and in no species throughout the range of Crustacea does it bear a palpus, or any corresponding appendage. In these par- ticulars it is unlike true maxillae. In some Schizopoda, as the Euphau- sia, it is a small, quadrate plate, consisting of two naked lobes in con- tact on the medial line ; and descending lower among Crustacea, the organ is a simple plate, with the lobes quite short and small. In the Caligi, the part corresponding to the lower lip forms the lower or pos- terior part of the buccal trunk. Such are in general the variations it undergoes.

Very different are the variations among the other mouth-organs. While in the Decapoda the lower lip is comparatively larger than in the Entomostraca, the maxillaj of the former are comparatively smaller than in many of the latter. Among the Entomostraca, these organs

HOMOLOGIES OF CRUSTACEA. 21

and the mandibles as well as the maxillipeds are often enlarged into feet, the palpus being much lengthened into a pediform or natatory ap- pendage. But this lower lip retains its fold-like character and par- takes of none of these modifications, being the same essentially in the highest and lowest species, excepting a diminution in size in the latter. The mandibles and maxillae it will be remembered form a con- tinuous series, alike in their relations and similar in their modifica- tions : while the lower lip, although following