448 AEACHNIDA 



mandibles with a tenninal claw; pedipalps 5-jointed and usually long, 



the terminal claw being sometimes bent down to form a grasping organ; 



legs usually 5-jointed, with or without swimming hairs, and joined to 



body by prominent coxal plates (Fig. 705, 1) ; a pair of spiracles on the 



dorsal side of the rostrum; genital i)ore surrounded by a plate and 



usually near the center of the body; numerous minute suckers often on 



each side of the genital pore; eggs laid on plants, stones, etc.; young 



born with 6 legs and usually go through a complex metamorphosis, often 



attaching themselves to aquatic insects : about 70 genera and 500 species, 



most of which live in fresh water, a few being found in brackish water 



or in the sea, and the genus Unionicola being parasitic in moUusks; about 



100 American species; 5 subfamilies. 



Key to the subfamilies of Hydrachnidae : 



Oi Large red mites with 4 eyes close together on a plate. 



bi Eye plate long and narrow 1. Limnocharinae 



fea Eye plate short, broad and paired 2. Eylainae 



Cj Eyes not close together on a plate, but far apart. 

 hi Pedipalps chelate. 



Ci Mandibles 1-jointed, straight and needle-like 3. Hydrachninae 



Cg Mandibles 2-jointed, the terminal joint a curved hook. 4. Hydryphantinae 

 63 Pedipalps not chelate 5. Hygrobatinae 



Subfamily 1. LIMNOCHAEINAE. 



Body very soft, variable in form, red in color; eyes 4, near together 

 on a long lanceolate plate : 2 genera. 



LiMNOCHARES Latreille. Body rectangular; legs without swimming 

 hairs, but with spines, and in 2 widely separated groups of 2 each: the 

 animals do not swim but walk slowly over the mud and plants in the 

 water; 2 species. 



L. aquatica (L.) (Fig. 703). Body red, 4 mm. long: on the bottom 

 of ponds; cosmopolitan and common; larvae attached to water skaters 

 {Hydrometridae ) . 



Subfamily 2. EYLAINAE. 



Body soft, regular in outline, red in color ; eyes 4, near together on a 

 paired plate: 2 genera. 



Eylais Latreille. Body oval, legs long, with swimming hairs, 

 rather close together; genital pore between the first 2 pairs: 35 species, 

 the larvae of which have been found on mosquitoes; 3 American species, 

 which are rapid swimmers. 



H. Lohinann, Das Tierreich, 1901. "A Roview of the Genera of the Water Mites," by 

 R. II. Wolcott, Trans. Am. Mic. See, Vol. 26, p. 161, 1905. "Die Siisswasserfauna 

 Deutschlands, Heft 12, Araneae und Acarina," by F. Koenike, 1909. 



