THE WATER FLEAS (CLADOCERA) 



69s 



29 (28) Rostrum and antennules pulex-Uke; post-abdomen tapered, not 

 sinuate Daphnia psittacea (Baird) 1850. 



General form like D. magna but smaller and more trans- 

 parent. Post-abdomen tapering, not sinuate, with about 10 

 anal teeth and many clusters of short, fine hairs. Claws with 

 two pectens, the distal having about IS teeth. Length, 9 , to 

 2.8 mm. besides spine of 0.8 mm.; J , to 1.8 mm. Nebraska, 

 in pools. 



Fig. 1063. Daphnia psittacea, note small secondary fornix 

 behind primary. 



0.5 MM 



30 (27) 



Secondary fornix rudimentary or very small. 

 rarely exceeding 10, usually fewer. 



Teeth of distal pecten 

 31 



31 (32, 33) Ocellus present; head not helmeted. 



Daphnia pulex (de Geer) 1778. 



Body stout and 

 heavy; usually not 

 transparent. An- 

 tenmiles very small, 

 the apex appearing as papillae on pos- 

 terior surface of rostrum. Post-ab- 

 domen without sinus; anus at end; 

 anal spines 12-17. Summer eggs 

 numerous; ephippium with two eggs 

 placed nearly vertically. 



Color red to yellow-brown, very variable. 

 Length, 9 , to 2.5 mm. In pools and lakes in 

 all regions; numerous varieties. 



Fig. 1064. Daphnia pulex. 



D. pulex includes a great number of 

 varieties, many of which have been de- 

 scribed as distinct species. The student 

 will be safe in assigning to pulex all opaque, 

 heavy-bodied forms with pectinate claws. 

 In many cases the identification of the 

 variety is more important than that of the 

 species, but the varieties have not been 

 worked out for this country. A few may 

 be noted: 



Figs. 1065,1066. 



Daphnia pulex, post-abdomen 

 and claw. 



Var. pulicaria Forbes. A semi-trans- 

 parent limnetic form, very close to pulex, 

 but more slightly built. Long spine. 

 Common in lakes. 



Var. clathraia Forbes. Only 12 anal 

 spines. Pecten with 3-4 large teeth. 

 Yellowstone. 



Var. minnehaha Herrick. Slight angle 

 over heart in adult 5 ; strong tooth in $ 

 and young. Minnesota and elsewhere. 

 Var. ohtusa Kurz. Spine very short or 

 absent. 9-10 anal spines. Rostrum long and pointed. Maine, Wisconsin, southern states. 



Var. curvirostris Eylmann. Rostrum very long and continued backward, lying close to 

 valves. Nebraska, CaliforDia. 



