8o6 



FRESH-WATER BIOLOGY 



KEY TO NORTH AMERICAN FRESH-WATER OSTRACODA 



1 (2) Second antenna two-branched; one branch rudimentary, immobile, 



the other elongate, flexible, with long natatory setae (Mvo- 

 DOCOPA); or both branches well developed, movable, and 

 natatory (CLADOCOPA) ; or both branches flattened, similar 

 tofeetof the Copepoda(PLATYCOPA). . . MARINE TRIBES. 

 These groups are not represented in fresh water so far as known. 



2 (i) Second antenna simple, subpediform, clawed at apex. Mostly fresh- 



water forms Tribe PODOCOPA . . 3 



3 (4) Three nearly similar pairs of legs. Furca rudimentary. Second an- 



tenna with nagellum (Fig. 1251 d l \ and little adapted for 

 swimming Family CYTHERIDAE . . 5 



4 (3) Two dissimilar pairs of legs. Furca commonly well developed. Sec- 



ond antenna, without flagellum and commonly with natatory 

 setae 9 



5 (6) Parasitic on gills of Crustacea. Terminal claws of legs with four large 



teeth (Fig. 1 249 a) Entocythere Marshall 1903. 



Only one species of this genus known. 



Entocythere cambaria Marshall 1903. 



Length 0.60 mm. Males abundant. Shell thin, frag- 

 ile and transparent. First antenna six-segmented. Sec- 

 ond antenna four-segmented. Flagellum unsegmented. 

 Caudal rami short and thick. Parasitic on gills of cray- 

 fish (Cambarus). Wisconsin. A most remarkable 

 form, in that Ostracoda rarely adopt parasitic habits. 



FIG. 1249. 



Entocythere cambaria. (a) End of third leg; 

 (6) Side view, X 50. (After Marshall.) 



6 (5) Not parasitic. Crawlers or burrowers. Terminal claws of legs with 



not more than two teeth, or plain (Fig. 1260^). 



Limnicy there Brady 1868 . . 7 



7 (8) Shell decidedly reticulate, with two lateral furrows. Furca blunt, 



about three times as long as wide (Fig. 1250 a). 



Limnicy there reticulata Sharpe 1897. 



Length 0.66 to 0.70 mm. and 0.25 mm. wide. Grayish 

 white. Shell conspicuously marked with a honeycomb- 

 like network of polygonal reticulations, and deep lateral 

 furrows (Fig. 12506). Furca (Fig. 12500) cylindrical, 

 thick and blunt, about three times as long as wide, with 

 two small setae. Posterior dorsal part of carapace tapers 

 to a point. Muddy bottom of ponds. Illinois, April. 



FIG. 1250. 



Limnicythere reticulata. (a) Furca; (6) Dorsal view; 

 (c) Side view, X 54- 



