Rhomballichthys Schwank, 1990

Balsamo, Maria, Pierboni, Lara & Grilli, Paolo, 2009, Taxonomic and nomenclatural notes on freshwater Gastrotricha, Zootaxa 2158, pp. 1-19 : 6

Genus Rhomballichthys Schwank, 1990

Schwank, P. 1990, Gastrotricha. In: Brauer A. (Ed) Süsswasserfauna von Mitteleuropa. Bd. 3/ 1: 1–252. G. Fis c he r Verlag, Stuttgart, p. 82.

Typus generis: Lepidoderma punctatum Greuter, 1917 ; original designation by Schwank (1990) as Rhomballichthys punctatus .

Schwank (1990) introduced the genus Rhomballichthys for three freshwater species with a complete cuticular covering of rhombic, unpedunculated scales, smooth or keeled, and with a very short, minute spiny process. These features combine those of three different genera ( Aspidiophorus , Lepidodermella , Heterolepidoderma ). Scale shape and habitus of the species remind the species of Aspidiophorus , which all have pedunculated scales. On the other hand, the Lepidodermella species have smooth scales and the Heterolepidoderma species have numerous, small, elliptical, generally keeled, unpedunculated scales. The typus generis of Rhomballichthys , R. punctatus (Greuter, 1917) is a species whose taxonomical position has been long debated: it was assigned to either Aspidiophorus or Lepidodermella and it was finally place into the latter genus due to the presence of unpedunculated, smooth scales, even if provided with a very short spiny extension (Balsamo 1983). Rhomballichthys murrayi is a new name introduced by Schwank (1990) for Chaetonotus sp. Murray, 1913: the original description of this species is quite incomplete and does not allow to define with certainty its morphological characters, so that it is a species inquirenda. Finally, Rhomballichthys carinatus is a new name introduced by Schwank (1990) for the specimens of Heterolepidoderma fallax Remane, 1936 reported by Roszczak (1969) from Poland. Schwank considered these ones as belonging to a different species from Heterolepidoderma fallax Remane, 1936 , that he includes among the species inquirendae. The assignment of the Polish specimens to a new species should require a careful revision of the distinctive characters: Rhomballichthys carinatus is considered here as a species inquirenda. The genus Rhomballichthys is maintained as a monotypic genus only including R. punctatus (Greuter, 1917) .