Histodytes microocellatus gen. et sp. nov. (Dracunculoidea: Guyanemidae), a parasite of Raja microocellata on the European Atlantic coast (north-western Spain).

We describe a new genus, Histodytes, within the family Guyanemidae (Nematoda: Spirurida: Camallanina: Dracunculoidea). The type species, Histodytes microocellatus n. sp., is found in the gill, heart, kidney, spleen and gonad tissues of Raja microocellata from the continental shelf off the estuary of Muros y Noia (north-western Iberian Peninsula). Histodytes differs morphologically from the three other genera described to date in this family ( Guyanema, Travassosnema, Pseudodelphys) because the vulva is situated a long way back from the oesophageal-intestinal union, and the anterior uterine branch almost reaches to the level of this union. In addition, it can be distinguished from Guyanema and Travassosnema by the absence of caudal alae in the male, and from Travassosnema by the much greater length of the glandular oesophagus and the lack of an oesophageal appendix. Histodytes is the only guyanemid genus described to date from an elasmobranch and the first one to be found on the European Atlantic coast.