CHAPTER II 



CRUSTACEA (COXTIX( T EI>) : ENTOMOSTRACA BRANCHIOPODA- 



PHYLLOPODA CLADOCERA WATER-FLEAS 



SUB-CLASS I. ENTOMOSTRACA. 



THE Entomostraca are mostly small Crustacea in which the 

 segmentation of the body behind the head is very variable, both 

 in regard to the number of segments and the kind of differentia- 

 tion exhibited by those segments and their appendages. An 

 unpaired simple eye, known as the Nauplius eye from its 

 universal presence in that larval form, often persists in the 

 adult, and though lateral compound eyes may be present they 

 are rarely borne on movable stalks. In the adult the excretory 

 gland ("shell-gland") opens on the second maxillary segment, 

 but in the larval state or early stages of development a second 

 ant.t'iinary gland may also be present, which disappears in the 

 adult. The liver usually points forwards, and is simple and 

 saccular in structure, and the stomach is not complicated by the 

 formation of a gastric mill. AVith the exception of most Clado- 

 cera and Ostracoda the young hatch out in the Nauplius state. 



Order I. Branchiopoda. 1 



The r.nmchiopods arc of small or moderate size, with flattened 

 and lobate post-cephalic limbs, and with functional gnathobases. 

 Median and lateral eyes are nearly always present. The labrum is 

 lar-'-e, and the second maxillae are small or absent in the adult. 



O ' 



Branchiopods arc found in every part of the world; a few are 

 marine, but the great majority are confined to inland lakes and 

 ponds, or to slowly-moving streams. The fresh waters, from the 



' For this use of the term P>r;iiidiio]io<l;i, cf. I'XIM^. Murph. Jalirl. viii., 1883. \>. 519. 



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