78 



SIPHONOSTOMA. 



SIPHONOSTOMA. 



790 



blance in form to that of certain Opbidians, particularly of the 

 Coronellce. The teeth very loosely constructed (effile'es), and very 

 much couched backwards ; the second row above, instead of forming 

 a curved line like the first, makes an angle rounded at its summit. 

 The diameter of the middle of the trunk is one twenty-sixth of the 

 total length of the body, round which there are 340 perfectly 

 annuliform folds. 



It is a native of Guiana. 



RhinatreitKi bivittatwn. a, its scales. 



SIPHONOSTOMA, an order of Suctorial Ci-ustacea. It was estab- 

 lished by Latreille, and comprehends all the Suctorial Crustaceans 

 whose thorax, composed of many distinct joints, is furnished with 

 natatory feet 



M. Milne-Edwards describes these animals as having the body 

 divided into three parts ; the head, the thorax, and the abdomen. 

 The first is large, and carries a pair of antenna;, a sucker furnished 

 with styliform mandibles, and anchor-like or prehensile jaw-feet, 

 generally three pairs in number. This cephalic portion of the body is, 

 in general, more or less clypeiform, and is confounded with one or two 

 of the first thoracic rings. The normal number of the constituent 

 segments of the thorax is five, but in consequence of the soldering of 

 the parts, this middle portion of the body offers mostly only two, 

 three, or four distinct joints. The last thoracic ring is apod, and, in 

 the female, carries two or three oviferous tubes. Finally, the abdo- 

 men is in general rudimentary, and is only furnished with a single 

 pair of appendages, disposed so as to constitute ordinarily a email 

 caudal fin. The general form of the body varies much, and some- 

 times departs considerably from that which may be considered as 

 normal in this class of annulose animals. 



The Siphonostoma undergo considerable metamorphoses in their 

 youth, and do not become parasites till they have changed their skin 

 once or many times ; they swim at first with ease, but after having 

 fixed themselves, they become more or less deformed, and do not quit 

 their place except slowly and with difficulty. 



M. Milne-Edwards divides the tyiphonoitoma into two families the 

 Pdtocephala and the Pachycefihala. 



Peltocephala. This family has less affinity with Cyclops than some 

 of the Pachycep/tala, but they offer a more complicated structure, 

 and consequently appear to M. Milne-Edwards to deserve precedence. 



The head is very large, shield-like, and in general much larger than 

 the thorax or abdomen ; it resembles a disc slightly convex above, 

 delicate on its edges, and truncated behind, where it is confounded 

 with the first rings of the thorax. On its upper surface two small 

 smooth eyes may be almost always distinguished; they are closely 

 approximated to the median line. Forward it is continued with two 

 frontal blades more or less distinct, and directed transversely. The 

 thorax is composed of a variable number of joints ; sometimes two 

 only are distinguishable, sometimes three or even four may be counted, 

 according as the three first segments are confounded with the head, 

 or this soldering extends to but two of these rings, or even to one 

 only. For the rest, the aspect of this portion of the body varies 

 much, for sometimes the dorsal segment of these rings presents nothing 

 remarkable, and sometimes it gives rise to great laming;, which resemble 

 the elytra of insects. 



The abdomen is but little developed, and presents no appendage 

 below, but terminates by two small natatory blades ciliated on the 

 edges, or by a species of trifoliated fin. 



The appendicular system presents, in all the animals of this division, 

 the same essential characters, and is composed of a pair of antenna), 

 a buccal apparatus, and four pairs of feet. 



The antennae, two in number only, are inserted very far from each 

 other, and are short, flattened, and directed outwards ; they are always 

 composed of two or three small lamellar joints, and are never setaeeous 

 nor annulated. 



The buccal apparatus is composed of a sucker, of divera rudi- 



mentary appendages, situated on each side of its base, aud of three 

 pairs of anchor-like jaw-feet. The sucker is large, conical, aud directed 

 backwards ; two unequal pieces are there to be diatiuguished, which 

 are soldered by the edges throughout the greatest part of their length, 

 but remain free towards the end, and leave between them, at the 

 summit of this species of beak, a circular or triangular aperture ; one 

 of these lamina; is inserted between the mouth and the front, and 

 represents the labrum, or upper lip ; the other, situated backwards, 

 is analogous to the lower lip of the masticating crustaceans. Between 

 the base of these two lips springs, on each side, an appendage, which 

 evidently replaces the mandibles of these last animals; but which, 

 instead of being short, stout, and dentiform, is slender, very much 

 elongated, and similar to a stylet with a dentilated point ; these styli- 

 form jaws penetrate into the beak by means of a slit situated near 

 its base, and advance into its interior, so as to come out by the termi- 

 nating aperture, and serve as a pair of lancets when the animal wishes 

 to suck its prey. A little outwards is found a second pair of append- 

 ages, which is reduced to a nearly rudimentary state, and seems to 

 be the representative of the first pair of jaws of the ordinary Crusta- 

 cea. In general there is to be distinguished near the same point u 

 styliform, or forked horny piece, which seems to be the vestige of a 

 third pair of buccal appendages, appendages which, in the masticating 

 crustaceans, constitute the second pair of jaws. The jaw-feet, three 

 pairs in number, offer considerable dimensions, and are ranged on each 

 side of the siphon: the first pair seems to be reflected (refoulecs) 

 forward, for they spring in front of the edge of the upper lip, between 

 the sucker and the antenna;, and by some naturalists they are con- 

 sidered as antenna; ; they are stout, short, more or less misshapen, 

 and each terminated by a hooked claw, by the aid of which the 

 animal attaches itself to its prey. The second pair of jaw-feet are 

 slender, and always composed of two principal joints of nearly equal 

 length, the second of which carries, near its middle, a small append age, 

 aud terminates by one or two hooks but little bent. The third pair 

 of jaw-feet, situated more backward, are stout, in general short, and 

 more or less completely sub-cheliform ; the crooked claw which termi- 

 nates them can be bent back on the penultimate joint, in manner of 

 a claw. 



The feet are four pairs in number, and are always more or less com- 

 pletely natatory ; two pairs, and sometimes all, terminate by two oars, 

 each composed of three joints, offering generally a very remarkable 

 disposition of a nature to favour their action as natatory instruments, 

 and which consist in a very considerable development of their basilary 

 joint, and the soldering of that joint with an unequal sternal pioce, 

 so as to form, with the whole, a single transversal blade, as for tho 

 two feet. It is even to be remarked, that in general this basilary 

 piece, which occupies the whole width of the corresponding ring, is 

 much more developed than the terminal oara of those liuibs, and con- 

 stitutes by itself nearly the whole of the fin formed by the pair of 

 feet thus modified. These four pairs of limbs belong to the first four 

 thoracic rings, and spring, some from the cephalic buckler, others 

 from the postcephalic portion of the thorax, varying in number accord- 

 ing to that of the thoracic rings, which are confounded with the 

 head. The last ring of the thorax carries none ; but in general si 

 pair of tubercles, or lobules, may be distinguished there, which 

 appear to be the vestiges of a fifth pair of limbs reduced to a rudi- 

 mentary state. 



These Crustaceans live as parasites upon fishes, but they are not 

 permanently fixed to them, and when they let go their hold, they Ci'a 

 change their place either by crawling slowly or swimming. The male 

 is in general distinguished from the female by some peculiarities of 

 structure, and by a very inferior size. The female nearly always 

 carries her eggs in cylindrical tubes, which spring near the posterior 

 border of the last thoracic segment on each side of the abdomen, aud 

 which often attain a very considerable length. The young, at their 

 birth, resemble the young of Cyclops, and must undergo many moults 

 before they finish their metamorphosis ; little however is known at 

 present of these changes. It is also to be noted that one often finds 

 in the neighbourhood of the vulva; small ampullee, which are fixed 

 there by a very narrow neck, and which may be spermatic reservoirs 

 analogous to those which M. Siebold made known in Cyclops. 



M. Milne-Edwards divides this natural family into three divisions 

 or tribes the Argulians, the Caligians, and. the Pandarians. 



The Argulians consist of a single genus, Argulut, which infests 

 fresh-water fish and the tadpoles of Batrachians, to which they adhere, 

 but they are also found free, swimming about with vivacity. 



A.foliaceus is known to most anglers : it is figured in Desmaresl 

 (' Crust.,' pi. 50, fig. 1), and there is a woodcut of it in Yarrell's 

 ' British Fishes,' vol. ii. p. 399. [ARGULUS.] 



Caligiam. There is nothing abnormal in the conformation of the 

 thorax of this tribe, the thoracic rings being simple, and without 

 dorsal appendages. The cephalic buckler is large, more or less oval, 

 delicate on its edges, and furnished anteriorly with very well-developed 

 frontal lamina;, the lateral extremity of which covers the base of the 

 antenna;. The posterior angles of this carapace are prolonged more or 

 less far on each side of the thorax, aud the portion of its posterior 

 border comprised between these two prolongations is confounded 

 with the first, or even the second or third first thoracic segments. 

 The result i*, that tho thorax is only composed of two, three, or 



