A preliminary revision of sordidus-like species of Ilyocryptus Sars, 1862 (Anomopoda, Branchiopoda) in North America, with description of I. bernerae n. sp.

Presently the inter-generic structure of the Ilyocryptus Sars, 1862 is not clear, and we regard as `sordidus-like' all the species with (1) incomplete moulting, (2) valves without lateral horns or other remarkable structures, (3) non-distal position of anus on postabdomen, (4) long lateral setae on the postabdomen, which reaches the anus; (5) single or doubled teeth on preanal margin of postabdomen. Available material on sordidus-like forms of Ilyocryptus Sars, 1862 (Anomopoda, Branchiopoda) from North America was investigated. We also analyzed a limited amount of material similar to I. sordidus s. str., but not enough to be presented now. Three other conventional species were found and redescribed: the exclusively North American I. gouldeni Williams, 1978, as well as I. cuneatusŠtifter, 1988 and I. spinosusŠtifter, 1988, both described earlier from Europe. An original analysis of the differences between all species was performed. A new sordidus-like species, I. bernerae n. sp., from a single locality in South Carolina, U.S.A., is described. The main diagnostic features of this new species within sordidus-like members of the Ilyocryptusare: thin and sharp dorsal keel; exclusively single preanal teeth, greatly increasing in size in basal direction; lateral setae on postabdomen, not decreasing in size basad; absence of denticles on base of postabdomen; complete absence of any denticles on distal and middle portion of ventral margin of postabdominal claws; distalmost spine on claw base longer than basalmost; bases of antennules compressed against each other (although not touching); slightly different armature of two sides of lateral swimming setae; presence of small hooks on tips of lateral swimming setae; distal segments of setae on trunk of limb I setulated only in basal portion; sensillum on gnathobase II curved.