xi PHYLUM ARTHROPODA 553 



appendages, except the first two in the male and the last in both 

 sexes, have the endopodite reduced or absent. The last pair of 

 abdominal appendages (uropods) expanded, and forming with 

 the telson a fan-like tail-fin. This, the only order of the Syncarida, 

 comprises the genera Anaspides, Koonunga, and Paranaspides 

 (Fig. 465). A related form is Bathynella, which, however, has only 

 one pair of abdominal appendages and no tail-fin. 



Division 2. Peracarida. 



Eumalacostraca in which the carapace, when present, leaves at 

 least four of the thoracic segments free. Heart elongated, tubular. 



ORDER 1. MYSIDACEA. 



Peracarida in which, though the carapace extends over the 

 greater part of the thorax, it does not coalesce dorsally with more 

 than the first three segments. The eyes, when present, are sup- 

 ported on movable stalks ; the antennules are biramous, and 

 the antennae have a scale-like exopodite or squame. The first 

 pair of thoracic appendages are specialised as maxillipedes. The 

 thoracic appendages (except sometimes the first and second pairs) 

 are biramous. The uropods with the telson form a broad fan-like 

 tail-fin. 



This order includes Mysis (Fig. 466), Lophogaster, and other 

 genera. 



ORDER 2. CUMACEA. 



Peracarida in which the carapace coalesces with the first three 

 or four segments of the thorax, is produced on each side to enclose 

 a branchial cavity, and in front is drawn out into a rostrum. The 

 eyes usually coalesce into one, which is not borne on a movable 

 stalk. The antennules are sometimes biramous ; the antennae 

 have no exopodites. Some of the thoracic appendages are 

 biramous. The telson may coalesce with the last segment of 

 the abdomen. The uropods are styliform, and there is no fan- 

 like tail-fin. 



Includes Cuma (Bodotria), Diastylis, etc. (Fig. 467). 



ORDER 3. TANAIDACEA. 



Peracarida in which the carapace coalesces with the first two 

 thoracic segments and is produced on each side to enclose a branchial 

 cavity. The eyes, when present, are usually supported on short 

 stalks which are not movable. The antennules are sometimes 

 biramous : the antennae may possess small exopodites. The first 

 pair of thoracic limbs are modified as maxillipedes. The second 

 and third thoracic limbs sometimes have vestigial exopodites. 

 The uropods are usually narrow. 



This order includes Apseudes, Tanais, Leptochelia, etc. 



