Eurycercus (Teretifrons) Frey, 1975

Bekker, Eugeniya I. & Kotov, Alexey A., 2016, A revision of the subgenus Eurycercus (Teretifrons) Frey, 1975 (Crustacea: Cladocera) in the Holarctic with description of a new species from Russian Arctic, Zootaxa 4147 (4), pp. 351-376 : 352-353

Subgenus Eurycercus (Teretifrons) Frey, 1975

Type species. E. glacialis Lilljeborg, 1887 . Typified by Frey (1975).

Amended diagnosis. Body uncompressed laterally, without a median dorsal keel. Dorsal head pores located on a flat head shield (no bubble-like projection or a transverse fold in this portion); ring of major head pore not elevated or elevated above head shield surface. Labral keel long, with angled apex reaching tip of antenna I or projecting beyond it. Intestine has a doubled loop; a posterior intestinal caecum absent. Entire shell serves as ephippium.

Comments. According to Frey (1975, P. 293), the diagnosis of this subgenus was: “shell broadly rounded, without a keel except in ephippial females; head pore not projecting at all, which makes the dorsal profile as seen from the side completely smooth and evenly rounded; head shield broadly rounded behind; labral keel large, expanded, acuminate in the middle; intestine with a double loop; no posterior intestinal caecum. In glacialis , in contrast to the other described species, the entire shell serves as the ephippium, with closure of the anterior portion accomplished by a complicated system of transverse infolding. If this occurs also in the other glacialis- like species, it can be elevated to a subgeneric character”. Hann (1990) accepted such diagnosis. But after our re-study of E. nigracanthus and description of E. chernovi sp. nov., the diagnosis needed updating, in particular regarding head pores and ephippium.