3S2 



ARTHROPODA 



LiTHODiD.i--, arc united as SCHIZOSOMI because the last thoracic segment is 

 free from the carapace and its appendages are rudimentary. LEI'COSOIDEA 

 (Oxystomata). Bodv o\al or triangular, area of mouth parts triangular. 

 Cahippa, Hcpali's/''' OXYRHYXCHA (Maioidea). Cephalothorax tri- 

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



Fig. 407. — B, Libinia cmarj^iiiala* spider crab (,from Emertoii). 



Mostly tropical. Hxasr Lihiiiia,''-' Pugcttia,'^ spider crabs. CY'CLOME- 

 TOPA. Body broader than long, arcuate in front. Canxrid.e, with last pair of 

 feet pointed. Cancer,'^ shore crab; Panopcus* mud crab. Portuxid.e, •with 

 last pair of feet flattened [saddles. Xcptuiiiis Inislatiis.'^ Avhen thin-skinned after 

 molting, is 'soft-shell crab.' C.\TOMETOP.A.. Front of carapace nearly 

 straight; body from above nearly quadrilateral; Gclasiiinis,'^ tiddler crabs, 

 Piiinotlicrcs ostrcuin,'^ common in oysters; Gec.^rcixid.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 eves, three or four free thoracic somites; 

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

 because combining arthrostracan and thoracostracan features. Didstvlis* 



Flu. 40S. — Didstylis i]uadrispiiiosus.* 



Order V. Syncarida. 



Especial interest also centres in Anaspiiics lasiiuinicr (and a few other forms) 

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

 They ha\e the stalked eyes, caudal fin, and biramous feet of a schizopod: 

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



