XII] CUMACEA 221 



abdomen is large and bears six pairs of flattened swimming limbs, 

 each of which carries a gill in its outer branch. 



Unlike most other Crustacea, Squilla and the other members of the 

 group do not carry their eggs about with them, but lay them in the 

 burrows in which they live, and by sitting over them and moving their 

 abdominal limbs they keep up a current of water which aeratesthe eggs. 

 They are exclusively marine and live buried in the sand or hidden 

 in crevices of the rock. They move actively and are difficult to catch. 



Sub-order 4. Cumacea (Peracarida pars). 

 The members of the sub-order Cumacea (Gr. KV/XXX, a wave, or 

 billow) are mostly small ; they live in the sea on sandy bottoms at 

 considerable depths, but come to the surface at night. They are 



f 



10 



7 

 FIG. 87. Female Diastylis stygiaxQ. After Sars. The carapace is 



represented as transparent to show the gill. 



1. Carapace. 2. First antenna. 3. First leg. 4. Gill borne on 

 first maxillipede. 5, 6, 7 and 8, second to fifth leg. 9. Free part 

 of thorax. 10. Abdomen. 11. Appendage of the last segment of 

 the abdomen. 



especially interesting because to a certain extent they are inter- 

 mediate in character between the Thoracostraca and the Arthro- 

 straca. Thus their paired eyes are not stalked and are some- 

 times fused together to form a single eye; the carapace is reduced 

 so as to leave several segments of the thorax uncovered (Fig. 87) 

 and on some of the thoracic legs there is a small exopodite. They 

 have a single pair of gills borne by the first thoracic limb the 

 so-called maxillipede. The exopodites of this pair of limbs lie in 

 grooves running foreward on the surface of the head. They are 

 folded into the form of tubes and convey away the water which has 

 passed over the gills. In the female the abdomen, which is long, has 

 lost all the limbs except the last pair. Like Mysis and its allies and 

 like all the Arthrostraca they have oostegites projecting inwards from 

 the bases of the thoracic limbs, which support the eggs. 



