OCR Text |
Show 80 CRUSTACEA. a single piece, which however is free behind, usually exposin the thoracic segments, bearing the three last pairs of feet a ~ having an articulation before that serves as a base to the ey: and intermediate antennro; these latter organs are always ex~ tended and terminated by two or three threads. The eyes are always approximated. The formation of the mouth is essentially the same as in the Dccapoda; but the pal pi of the mandibles! instead of .b~ing laid on them, are always vertical. The foot-Jaws are deprived of the flagelliform appendage presented to us by the same parts in the Decapoda. They have the form of claws or of small feet, an~, at least in severalthe Squilloo,-their external base as well as that of the two anterior feet properly so called, exhibits a vesicular body. Those of the s.econd pair, in the same Stomapoda, are much -larger than the others and even than the feet, which has caused them to be considered as true feet; fourteen of 'them have been counted( I). The four anterior feet have also ·the form of ?laws, but are terminated as well as the foot-jaws by a hook ~hiCh curves towards the head, on the inferior and anteriOr edge of the preceding joint or of the hand. In others how. ever-the Phyllosoma for instance(2)-all these organs are filiform and have no forceps. Some of them at least as well as the last six and equally simple ones of the Stomap~da pro· vided with claws, have an appendage or lateral branch. The seven last segments of the body, containing a large portion of t~e heart and furnishing a base for the attachment of the res· p1ratory or~ans, can no longer in this respect be assimilated to that portiOn of the body which is called the tail in the De· capoda : it is a _true ab~omen. Its penultimate segment has a fin on each s1de formed like the caudal of the Macroura but ~s frequently, as well as the last segment or intermediat; portion, armed with spines or teeth. (l) The second jaws of these Stomapoda no longer present the same form as ~bose of the Decapoda. They have the figure of an elongated triangle divided d mto four segments by transverse lines. The mandibles are bifurcated and well en tate d. (2) IR all those where the four anterior feet are in the form of claws the six laJt are natatory. ' 81 The Stomapoda are all marine Crustacea. Their favourite habitat is in the intertropical latitudes, and they are not found beyond the temperate zones. Of their habits we are totally ignorant; that those which are furnished with claws use them in seizing their prey, in the manner of those Orthoptera called in Provence Pregadious or Mantes( I), we cannot doubt. Hence their vulgar appellation of Sea-:Nlantis: they are the C1·angones and Crangines of the Greeks. According to Risso they prefer sandy bottoms in deep water, and copulate in the spring. Other Stomapoda, those of our second family, being less favoured with natatory appendages and having a much flatter and more superficially extended body, are generally found on the surface of the water, where they move very slowly. We will divide the Stomapoda into two families. FAMILY I. UNIPEL TAT A. In this family the shell consists of a single shield, of an elongated quadrilateral form, usually widened and free behind, covering the head, the antennre and eyes excepted which are placed on a common anterior articulation, and at least the first segments of the body. Its anterior extremity terminates in a point or is preceded by a small plate with a similar end. All the foot-jaws, the second of which are very large, and the four anterior feet are closely approximated to the mouth on two inferiorly converging lines, and have the form of claws with a single finger or mobile and flexed hook. With the exception of the second feet all these organs are furnished at their external origin with a little pediculated vesicle. The other six feet, at the base of whose third segment is a lateral appendage, are linear, terminated by a brush, and simply na- (1) Some other analogous Orthoptera, such as the Phyllium, resemble leaves. The Phyllosom<e, Crustacea. of the 10ame order, exhibit similar affinities. VoL. Ili.-L |