382 



ARTHROPODA 



LITHODIDJF, are united as SCHIZOSOMI because the last thoracic segment is 

 free from the carapace and its appendages are rudimentary. LEUCOSOIDEA 

 (Oxystomata). Body oval or triangular, area of mouth parts triangular. 

 Calappa, Hepatus* OXYRHYNCHA (Maioidea). Cephalothorax tri- 

 angular, narrowed in front; mouth area (as in the following tribes) quadrilateral. 



FIG. 407. B, Libinia emarginata* spider crab (from Emerton). 



Mostly tropical. Hyas* Libinia* Pugctiia* spider crabs. CYCLOME- 

 TOPA. Body broader than long, arcuate in front. CANCRID^E, with last pair of 

 feet pointed. Cancer* shore crab; Panopeus,* mud crab. PORTUNID^E, with 

 last pair of feet flattened paddles. Neplunus hastatus* when thin-skinned after 

 molting, is 'soft-shell crab.' CATOMETOPA. Front of carapace nearly 

 straight; body from above nearly quadrilateral; Gelasinms,* fiddler crabs, 

 Pinnotheres ostreum* common in oysters; GECARCINID^E (Uca, etc.), land crabs 

 of the tropics, which only go to the sea at the reproductive season to lay their 

 eggs. 



Order IV. Cumacea. 



Small marine forms with sessile eyes, three or four free thoracic somites; 

 appendages biramous; a brood sac beneath the cephalothorax. Of interest 

 because combining arthrostracan and thoracostracan features. Diastylis.* 



FIG. 408. Diastylis quadrispinosus.* 



Order V. Syncarida. 



Especial interest also centres in Anaspides tasmanicr (and a few other forms) 



from lakes in Tasmania, which unite schizopod and amphipod characters. 



They have the stalked eyes, caudal fin, and biramous feet of a schizopod; 



otocysts in the antennulae like a decapod; but agree with the amphipods in shape 



