428 



ARTUIiOPOBA. 



Order I. ScMzopoda. 



These are small forms, mostly marine, in which the cephalo- 

 thorax is covered by a carapace with which some or all of the 



Yia. i'ii.— AmphWuH'. (From Gerstacker.) a', a^ first and second antennae; ou, eye; 

 Vll-Xlll^ the seven free thoracic segments ; 1-1, abdominal segments. 



thoracic somites are firmly united. The eight thoracic feet retain 

 throughout life a biramous condition and are used in swimming. 

 The posterior pair of abdominal feet together with the telson form 



Fig. 434. — Mi/^is elongata. (From Gerstacker.) a, j3, first and second antennre, a, ex- 

 pedite; ally eye; /, endopodite; o, otocyst ; 1-7, al)doniinal somites. 



a caudal ' fin ' by means of which tlie animal can swim backwards. 

 The delicate skin permits of diffuse respiration, and gills are fre- 

 quently lacking. In some genera plates from the legs of the female 

 enclose a brood case beneath the cophalothorax, thus giving these 

 forms the common name of opossum shrimps. 



