288 



COMPARATIVE ANATOMY 



CHAP. 



THE CRUSTACEA. 

 Systematic Review. 



Sub-Class I. Entomostraca. 



Fig. 191. Branchipus stagnalis, male. 01, Anterior an- 

 tenna; ; a-2, posterior antennae, seizing antennae with accessory 

 appendages ; ua, unpaired eye ; I, liver ; md (above), mandible ; 

 sd, shell gland ; h, heart or dorsal vessel ; oh, slit-like apertures 

 (ostia) of the heart ; md (below), intestine ; p, penis ; br, branchial 

 sac ; bri, branchial leaflet ; pa, paired stalked eyes (after Glaus). 



The trunk consists of a 

 varying number of segments. 

 AVe can here often distin- 

 guish an anterior division 

 bearing limbs from a pos- 

 terior division which has 

 no such appendages. Each 

 division, however, consists of 

 a varying number of seg- 

 ments. The genital aper- 

 tures usually lie between the 

 two divisions of the trunk. 

 A dorsal shield is often 

 present, and is developed in 

 various ways. The limbs 

 are very variously shaped. 

 Besides the usual lateral 

 eyes, the unpaired frontal 

 eye of the Nauplius larva is 

 retained by the adult animal. 

 A masticatory stomach is 

 wanting. A Nauplius larva 

 is hatched from the egg. 

 Mostly sinall animals. 



Order I. Phyllopoda. 



With swimming feet 

 which carry branchial sacs, 

 mandibles without feelers, 

 and reduced maxillse. 



Sub-Order 1. Branchiopoda. 



Body distinctly seg- 

 mented with numerous 

 trunk segments, and numer - 

 ous pairs of swimming feet., 

 Carapace seldom wanting, 

 either flat and shield-shaped 

 or in the form of a bivalve 

 shell. Heart an elongated 

 dorsal vessel with numerous 

 pairs of ostia. In fresh 

 water. Branchipus (Fig. 

 191) (without shell), Apus 

 (with flat carapace), Es- 

 theria, Limnadia (with bi- 

 valve shell). 



