Reinvestigation and reinterpretation of Chordodiolus echinatus Linstow, 1901, a peculiar nematomorph species

Abstract

The Central African nematomorph species Chordodiolus echinatus Linstow, 1901 is characterized by bilateral rows of bristles in combination with a terminal cloacal opening at the posterior end of the holotype. This specimen has been interpreted as a male while further specimens with a bilobed posterior end and a ventral cloacal opening have been described as females. The assignment of characters to males and females in C. echinatus represents inverted patterns compared with all other freshwater Nematomorpha. This present reinvestigation using light microscopy and scanning electron microscopy reveals that the holotype of C. echinatus contains oocytes and, therefore, represents a female. Consequently, C. echinatus shows structures typical for gordiids with the exception of the bilateral rows of cuticular bristles at the female posterior end. The cuticle is similar to the one of Beatogordius raphaelis and C. echinatus appears as a species derived within the genus Beatogordius and must therefore be renamed as Beatogordius echinatus.