Pararhyacodrilus, Snimscikova, 1986

Timm, Tarmo, 2020, A literature revision of Pararhyacodrilus Snimščikova, 1986, with the erection of a new genus, Semernodrilus gen. nov. (Oligochaeta, Tubificidae, Rhyacodrilinae), Zootaxa 4786 (3), pp. 431-436 : 433

On Pararhyacodrilus

The diagnosis of the genus Pararhyacodrilus after Snimščikova (1986, p. 203) reads as follows (translated from Russian by T.T.): “In ventral bundles bifid chaetae, in the dorsal bundles hair and bifid chaetae. Dorsal bifids in bundles together with hair chaetae, without intermediate denticles. In the subsequent segments, without hair chaetae, the bifids resemble ventral chaetae. Ventral chaetae either with longer distal tooth, with equal teeth, or with proximal tooth longer and thicker. Ventral chaetae of segment XI modified as penial, either with two reduced teeth or simple-pointed, several per bundle. Coelomocytes present in the body cavity. Reproductive organs in the segments typical of the family. Atria pyriform or roundish. Atrial ampullae covered with a layer of prostatic cells. Spermathecae with roundish ampulla, connected with intestine, and with short external duct. Sperm amorphous, not assembled into spermatozeugmata.”

Proceeding from the above discussion, the connection between the spermathecae and the intestine is the only di- agnostic character separating the genus Pararhyacodrilus from Rhyacodrilus . This character is furthermore unique in Tubificidae with hair chaetae [ Tubificidae here in the traditional understanding; in the classification of Erséus et al. (2008) and followers, these would be equivalent to all subfamilies of Naididae except Naidinae and Pris- tininae]. The only two valid species corresponding to the diagnosis of this genus are Pararhyacodrilus aspersus Snimščikova, 1986 (type species, in Lake Baikal) and P. ekmani ( Piguet, 1928) (syn. Rhyacodrilus ekmani, in Lake Vättern , Sweden). Two more taxa associated with Pararhyacodrilus in the literature, i. e. Rhyacodrilus palustris ( Ditlevsen, 1904) (syn. Ilyodrilus palustris ) and Rhyacodrilus profundalis Lastočkin, 1937 (syn. Rhyacodrilus ekmani var. profundalis ), do not belong to this genus, as has been shown above. As to Pararhyacodrilus confusus , see below.