Description of Gyrodactylus notatae n. sp. (Monogenea: Gyrodactylidae) from Menidia menidia (L.) (Actinopterygii: Atherinidae) in Nova Scotia, Canada.

Gyrodactylus notatae n. sp. (Monogenea: Gyrodactylidae) is described from the fins and gills of the Atlantic silverside Menidia menidia (L.) (Atherinidae) inhabiting the brackish water of Lawrencetown Lake, Nova Scotia, Canada. G. notatae n. sp. is the first monogenean to be reported from M. menidia. It is characterised by having stout hamuli, a ventral bar with small anterolateral processes and a linguiform membrane, a cylindrical dorsal bar, a male copulatory organ (MCO) with a single large and only three small terminal spines, and a marginal hook sickle that is wider distally than proximally. The new species most closely resembles species of the G. wageneri-group, particularly G. pungitii Malmberg, 1964, but is distinguished by the smaller dimensions of all of its haptoral components. The morphological description of G. notatae is supplemented with 1,028 sequenced base pairs (bp) of ribosomal DNA (rDNA) spanning the ITS-1, 5.8S and ITS-2 regions, with which a BLAST (Basic Local Alignment Search Tool) search failed to provide close matches (c.80%). G. notatae is only the second species of viviparous monogenean to be described from species of Menidia, the other being G. nannus Rogers, 1968 from M. beryllina (Cope) in the southern USA. The two species appear to be from different lineages within Gyrodactylus von Nordmann, 1832.