2S5 



ISOPODA. 



ISOPODA. 



Cuvier, the two anomalous chords composing the mesial part of the 

 nervous system of the Onisci (and probably of the other hopoda, and 

 even of the Amphipoda) are not entirely approximated, and may be 

 well distinguished throughout their length. There are nine ganglions, 

 without counting the brain ; but the first two and the last two are 

 so approximated that they may be reduced to seven. The second and 

 the six following furnish the nerves to the seven pairs of feet ; the 

 four anterior feet, although analogous in the order of succession of the 

 parts to the last four jaw-feet of the Decapoda, are really feet, properly 

 BO called. The segments which immediately succeed, or those that 

 form the tail, receive their nerves from the last ganglion. These 

 segments may be considered as simple divisions of a single segment, 

 represented by that ganglion ; and we accordingly see that the number 

 of these posterior segments varies. . 



The following is the arrangement of M. Latreille : 



The order consists of six sections. 



1. F.PICARIDE3 (Latreille). These are parasitical Isopoda, which, 

 according to M. Latreille, are without either eyes or antenna; ; the 

 males however have eyes, though the females are blind. The body is 

 flat, very small and oblong in the males, but much larger in the 

 females, taking in their case the form of an oval, which is narrowed 

 and a little curved posteriorly, hollow below, with a thoracic border, 

 divided on each side into five membranous lobes. On this border 

 the feet, which are very small and unfit either for walking or swim- 

 ming, are situated. The under part of the tail is furnished with five 

 pairs of small ciliated imbricated leaflets, answering to as many 

 iegments, and disposed in two longitudinal rows ; but the posterior 

 extremity is deprived of appendages. The mouth presents distinctly 

 only two membranous leaflets applied one upon the other, of the 

 same consistence, and quadrilateral. The lower concavity, forming a 

 sort of flat basket, is filled with eggs. Near the place of their issue 

 is constantly found an individual, which is presumed to be the male ; 

 but M. Latreille adds, thr.t the extreme smallness of its size seems to 

 forbid the possibility of copulation. According to M. Desmarest, this 

 individual is furnished with two eyes ; its body is straight and nearly 

 linear. One sub-genus only belongs to this section. 



Bopyria (Latreille). The most common species is B. Crangorum. 

 Those who are in the habit of eating prawns will probably have 

 observed a tumour occasionally presenting itself under the carapacj 

 on one of the sides, which is bulged our On lifting this part of the 

 shell, the parasite will, in such cases, be discovered immediately 

 under it and upon the branchia). We have frequently detected the 

 Bopyrus, but on whatever species of prawn it has been found, we 

 have never remarked that the nnimul to which it adhered was more 

 meagre than its fellow?, though this perhaps may have arisen from 

 the prawn not having been long subject to the visitation of the 

 parasite. But there is another reason why the prawn should not 

 suffer much from the adhesion of the parasite. The author of ' Horfc 

 Eutomologiete ' informs us that he has lately found three specimens 

 of Bopyriu (females) with their backs turned to the branchiaj of 

 the prawns; and he is or opinion that they and other crustaceous 

 par.i-itec which adhere to the anterior parts of fishes and Crustacea, 

 fix themselves there for the sake of the currents (produced by the 

 branchiae in respiration), which bring with them the animalcules on 

 which the parasites feed. 



Crnngvrwn. 



a, the tipper aide ; I, the animal Bern in profile ; c, the under side ; rf, one 

 of the fict, inufh magnified (foni:il>') ; <, Mnall individual, considered as the 

 mate, upper sidr ; /, th<* fame, lower side ; g, carapace of a Prawn deformed on 

 the right side by the pretence of Uupynn. (Desmarest.) 



B. Crangorum is found on Palemon servatm and Palemon squilla, 

 but most frequently on the former. 



M. Risso has described another specie?, under the female of which 

 he states that he found 800 or 900 living young ones. 



2. CTMOTHOADA (Latreille). This section comprises those Isopodce 

 which have four very apparent antenna;; these are setaceous, and 

 nearly always terminated by a pluriartieulate stem. These crustaceans 

 have eyes, a mouth of the ordinary formation, vesicular branchia), 

 disposed longitudinally in pairs, a tail consisting of from four to 

 six segments, with a fin on each side, and the anterior feet most 

 frequently terminated by a strong but small nail or hook. These 

 Isopodce are all parasitic according to Latreille ; but Serolis appears 

 not to be a parasite. Sometimes the eyes are mounted on tubercles 

 at the summit of the head. The tail is composed of only four 

 segments. 



Serolis (Leach). One species only known, S. Falricii (Cymothoa 

 paradoxa of Fabricius). Antenuto placed on two lines, and termi- 

 nated by a pluriarticulate stem. Under the first three segments of 

 the tail there are between the ordinary appendage three others, which 

 are transverse, and terminated posteriorly in a point. 



M. Desmarest describes the animal thus: -Superior antenna! 

 formed of four joints, larger than the first three of the inferior 

 antenna; ; the last joint composed of many others, and smaller. 

 Inferior antenna) with five joints, the first two small ; the third and 

 fourth (principally this last) elongated ; the fifth composed of many 

 others, smaller. Second pair of feet having the penultimate joint 

 enlarged and the nail or claw much elongated ; the sixth pair ambu- 

 latory, rather spiny, and having the nail slightly curved. Anterior 

 appendages of the belly, or branchial lamina;, formed of two equal 

 parts, which are foliaceous, rounded at their extremity, furnished 

 with hairs at their base, placed upon a common peduncle ; the two 

 posterior and lateral appendages small and narrow, especially the 

 interior one, which hardly projects. 



This is a very interesting animal, and has been considered to offer 

 some resemblance at first sight to the extinct form of the Trilolites. 

 [TRILOBITES.] 



Serolis Falricii, 



a, back ; 6, under surface, showing the union of crustaceous legs with tho 

 membranous bronchia! ; c, magnified view of branchiffl. . 



This creature has been found at Tierra del Fuego, Straits of 

 Magalhaens (Banks), and Senegal (Dufresne). Captain Phillip Parker 

 Kins, R.N., collected many specimens on the east coast of Patagonia, 

 and also at Port Famine, in the Straits, where Captain King saw the 

 beach covered with dead specimens. Ho also observed them alive 

 swimmii.g close to the bottom among the sea-weed. They moved 

 slowly and gradually, unlike a shrimp. He never saw them swimming 

 near the surface : their legs seemed adapted for swimming and 

 crawling on the bottom. 



Cymothoa (Fabr.) Antenna! nearly equal in length ; eyes but little 

 apparent ; last segment of the tail squared, and the two pieces termi- 

 nating the lateral fins linear, equal, and styliform. 



Cymnthoa oestrum, 

 a, upper side ; ft, lower side. 



