352 THE INVERTEBRATA 



n cgr 



Fig. 256. Anaspides tastnaniae, x 3. From Woodward, cgr. mandibular or 

 "anterior cervical" groove; 11, viii, second and eighth thoracic somites; 

 I, 6, first and sixth abdominal somites. 



Subclass PERACARIDA 



Malacostraca whose carapace, if present, does not fuse with more 

 than four thoracic somites ; whose eyes may be stalked or sessile ; and 

 which possess oostegites; a more or less elongate heart; and a few 

 simple coeca on the mid gut. 



A large subclass, containing several orders, which range from the 

 prawn-like Mysidacea, in which the caridoid facies (pp. 347, 348) is 

 practically intact, to the Isopoda and Amphipoda (slaters and sand- 

 hoppers) in which the carapace is lost and other features are greatly 

 modified. The important common characters which all these orders 

 possess are the presence of oostegites and the retention of the 

 young, which are directly developed, in a brood pouch formed by 

 those organs. Certain peculiarities, however, of the mandibles, which 

 bear behind the incisor process a movable structure known as the 

 lacinia mobilise of the thoracic limbs (p. 300), etc., are also possessed 

 in common by the Peracarida 



Order MYSIDACEA 



Peracarida with a carapace which covers most or all of the thoracic 

 somites; the eyes (when present), stalked; the scale of the antenna 

 well developed; exopodites on most or all of the thoracic limbs, of 

 which one or two pairs are maxillipeds; and a well-formed tail fan. 

 Small, usually pelagic crustaceans, most of which are marine, 

 though a few occur as " relicts" or immigrants in fresh waters. They 

 are mostly carnivorous, but take vegetable matter in the course of 

 feeding. Small food particles are obtained in the current set up by 

 the exopodites of the maxillae and when there are no gills also by a 

 whirling action of the thoracic exopodites, and are strained oflP by 



