288 



Stomapoda.- 



-CRUSTACEA.- 



-Amphipoda. 



victim, clothing themselves with its spoils. They run 

 about with great rapidity, and when seized draw them- 

 selves into the shell with a sudden snap, close the aper- 

 ture with their stout claws, and resist strongly all at- 

 tempts to pull them out. When young they may be 

 found inhabiting small shells, such as the periwinkle, 

 &o., but as thej' increase iu size they take possession 

 of the large whelk or buccinum. 



Ordeb II.— STOMAPODA {Sea-Mantes). 



The Slomapoda are distinguished from the Decapoda 

 by their not possessing internal branchiae or gills. These 

 organs when present are external, and generally spring 

 from the basal joint of the abdominal false feet. Some- 

 times they are fixed at the base of the thoracic feet, and 

 are suspended under the thorax. The carapace varies 

 in form and size, sometimes covering the whole thorax, 

 or at others only part. The abdomen varies much iu 

 appearance also. In general it resembles that part of 

 the body in the Macroura, and terminates in a caudal 

 fin, which fits them for swimming. The feet are seven 

 or eight pairs, and in most of the species are placed 

 near the mouth, or are folded upon it, hence the name. 

 In some genera of this order the thoracic feet are slen- 

 der, resemble each other in form, and are all adapted 

 for swimming. In others, the first pair are large and 

 prehensile, and the three succeeding pairs are also claw- 

 shaped and formed for prehension. 



Mysis. — Amongst those of the first group we may 

 mention the genus Mijsis, the species of which are 

 known by the name of the Opossum shrimps. They 

 derive this name from their carrying their eggs and 

 young in a pouch beneath the thorax and between the 



Fig. 183. 



thoracic legs. The species are small and have the 

 body narrow and elongated, like the shrimps. They 

 are found in vast numbers, especially in the northern 

 seas, where they constitute a large portion of the food 

 of the whale, and are luminous at night. 



In this group we have also the curious crustaceans 

 belonging to the genus Phyllosoma, the body of which 

 is transparent and so completely flattened, that it is 

 difficult to understand how the viscera have room to 

 play. 



In the second group we may mention the genus 

 SquiUa. 



THE MANTIS CRAB {SquiUa 

 Desmarcstii — tig. 186) is about 

 seven inches in length. Its 

 carapace only covers the an- 

 terior half of the thorax, the 

 hinder being formed of rings 

 like those of the abdomen. It 

 is provided with enormous 

 claws, terminating in a sharp 

 hook; the last joint furnished 

 with six sharp projecting 

 spines, and the preceding joint 

 with three, and so hollowed as 

 to render this claw a most effi- 

 cient instrument of prehension. 

 They bear a considerable re- 

 semblance to the fore legs of 

 the Orthopterous genus of in- 

 sects. Mantis; hence the popu- 

 lar name applied to the species 

 of this genus. This species is 



a native of the seas of Europe, but the greater number 

 are inhabitants of tropical seas. 



Sea Miiiitis. 

 or Maatis Crab. 



Section IL— SESSILE-EYED CRUSTACEA (Edriophthalma). 



The Sessile-eyed Crustaceans are distinguished from 

 the Stalk-eyed, or PodojiJdhalma, by their branchiae, 

 or gills, not being organs specially formed for the pur- 

 pose of respiration, but constituting a part of the organs 

 of motion, their structure being peculiarly adapted to 

 serve that end ; and by their eyes not being placed on 

 foot-stalks, but being sessile and immovable. They 

 have no thoracic carapace; but the thorax and abdo- 

 men are composed of a series of rings or joints, sepa- 

 rate from each other and movable. The head is 

 distinct from the thorax. 



They are divided into three orders — AMPniPOD.4, 

 L^MODIPODA, and Isopoda. 



Order I.— THE AMPHIPODS {Amphipoda). 



The Amphipods have tlieir branchiae or gills in the 

 form of large membranous vesicles placed at the base 

 of the feet, on their inner side. The thorax is gene- 

 rally divided into seven movable rings, and the 

 thoracic, or true feet, are seven pairs. The abdomen 

 is large and well developed, and the members, or false 



swimming feet attached to it, are elongated, naiTow, 

 and fringed with hairs. The three hinder pairs are 

 bent backwards, and, along with the terminal portion 

 of the abdomen, form a sort of fin, which serves the 

 animal for swimming or leaping. The females carry 

 their eggs under the thorax, between certain scales or 

 vesicles, which form a kind of pouch. In this position 

 they are hatched, and the young remain attached to 

 the legs, or other parts of the body of the parents, until 

 they gain sufficient strength to swim and take care of 

 themselves. The order contains a considerable num- 

 ber of species, all of small size— some are parasitical, 

 living attached to fishes, and in Medusae or Acalephse. 

 Such are the species of the genus Phronima, one or 

 two of which are European, and are found inhabiting 

 the interior of a gelatinous, transparent, hell-like bag, 

 open at both ends, and formed probably of the body of 

 a Beroe. Others are free and very activb. some living 

 in the sand of the sea-shore, others in the oea or fresh- 

 water. 



Talitrus. — The species of this genus are well 

 known by the name of Sandhoppers, or Sea-fleas. 



