306 



MANUAL OF ZOOLOGY. 



ORDER I. STOMAPODA. In this order there are generally 

 from six to eight pairs of legs, and the branchm, when present, are 

 not enclosed in a cavity beneath the thorax, but are either suspended 

 beneath the abdomen, or, more rarely, are attached to the thoracic 

 legs. The shell, also, is thin, and often membranous. From 

 all the preceding orders the Stomapoda are, of course, distin- 

 guished by the possession of pedunculate eyes. The develop- 

 ment of the Stomapoda would appear to be by means of " Zoeae." 

 All the Stomapoda are marine, with the single exception 

 of the My sis relicta of the great lakes of Sweden and North 

 America; and the Locust Shrimp (Squilla mantis] may be 

 taken as a good example of the order. In this Crustacean 

 (fig. 156) the carapace is small, and does not cover the pos- 

 terior half of the thorax. The 

 eyes and antennae are attached 

 to a somite which is not solder- 

 ed to the cephalothorax. Sev- 

 eral of the anterior appendages 

 are developed into powerfully 

 prehensile and hooked feet. 

 The branchiae are attached to 

 the first five pairs of abdominal 

 feet. The three posterior tho- 

 racic and the abdominal ap- 

 pendages are in the form of 

 " swimmerets," and the tail is 

 expanded into a powerful fin. 

 Besides the Locust Shrimps, 

 the order includes the Glass 

 Shrimps (Erichthys] and their 

 allies, and the Opossum Shrimps 

 (Mysis). 



ORDER II. DECAPODA. The 

 members of this order are the 

 most highly organised of all the 

 Crustacea, as well as being 



Fig. 156. Squilla mantis, the Locust 

 Shrimp. 



those which are most familiarly 

 known, the Lobsters, Crabs, 

 Shrimps, &c., being comprised under this head. For the most 

 part they are aquatic in their habits, and they are usually pro- 

 tected by strong resisting shells. There is always a compli- 

 cated set of " gnathites," or appendages modified for masticat- 

 ory purposes, surrounding the mouth. The ambulatory feet are 

 made up of five pairs of legs (hence the name of the order) ; the 

 first pair and often some other pairs behind this being "che- 



