Redescription of Rhabdochona cotti (Nematoda, Rhabdochonidae) from Cottus caeruleomentum (Teleostei, Cottidae) in Maryland, USA, with remarks on the taxonomy of North American Rhabdochona spp.

The nematode Rhabdochona cotti Gustafson, 1949 is redescribed from specimens collected from the intestine of the blue ridge sculpin Cottus caeruleomentum (a new host record), a recently described fish species, from Little Fishing Creek in Maryland, USA. The measurements of these specimens, collected in November 2005, are generally smaller than those reported in the original description of R. cotti, this being probably associated with the nematode’s seasonal maturation cycle or the different host species. As revealed by SEM, the deirids of R. cotti are simple (not bifurcate), in which this species differs from almost all North American congeners. Of these, simple deirids, filamented eggs and a rounded tail tip in females occur only in Rhabdochona longleyi, but it distinctly differs from R. cotti in the smaller number of anterior prostomal teeth (6 vs. 14). Rhabdochona rotundicaudatum is considered a junior synonym of Rhabdochona cascadilla; numerous specimens of the latter were collected from Semotilus atromaculatus, Luxilus cornutus and Notropis rubellus from the type locality (Eramosa River, Ontario, Canada) (unpublished). Rhabdochona paxmani and Rhabdochona salmonis are synonymized with Rhabdochona kisutchi, whereas Rhabdochona californiensis is considered a junior synonym of R. cascadilla. The need of a taxonomic revision of North American species of Rhabdochona is stressed.