50 THE LIFE OF CRUSTACEA 



Mysidacea, the epipodite of the maxilliped ; but in 

 this order it forms a gill, and usually carries a row 

 of flattened gill lobes. 



The third Order, that of the Tanaidacea (Fig. 19), 

 is of special interest, since in many respects it forms 

 a transition to the next. It comprises a number of 

 minute Crustacea, generally found burrowing in mud 

 in the sea. They have a small carapace, which only 

 involves the first two thoracic somites, the rest of 



ex. 



Fig. 19 — Apseudes spinosus, One of the Tanaidacea. En- 

 larged. (From Lankester's " Treatise on Zoology," after 

 Sars.) 



ex, Vestiges of exopodites on second and third thoracic limbs ; oc, 

 the small and immovable eye-stalks ; sc, scale or exopodite of 

 antenna ; ur, uropod ' 



the somites being distinct. The side-folds of the 

 carapace enclose a pair of small cavities, within 

 which lie, as in the case of the last two orders, 

 the epipodites of the maxillipeds. The eyes are not 

 movable, although they are set on little side-lobes of 

 the head, representing the vestiges of eye-stalks. The 

 first pair of thoracic limbs are maxillipeds, and the 

 second pair are very large, and form pincer-claws 

 (chelae). Minute vestiges of exopodites are some- 



