Description of a new marine predatory nematode Latronema dyngi sp. nov. (Nematoda, Chromadorida, Selachinematidae) from the west coast of Sweden and an updated phylogeny of Chromadoria

A new nematode species, Latronema dyngi sp. nov., is described from Skagerrak off the west coast of Sweden with the type locality near Dyngö island. Latronema dyngi sp. nov. is characterized by multispiral amphideal fovea with circular outline, 0.2–0.3 corresponding body diameters wide in males and 0.1–0.2 corresponding body diameters wide in females, 12 cuticular longitudinal ridges and 18–27 precloacal supplements in males. Latronema dyngi sp. nov. most closely resembles L. orcinum in terms of body length; demanian ratios a, b, c and c′; number of amphid turns in males; and the ratio of spicule length to cloacal body diameter. The two species can be differentiated by the number longitudinal ridges on the cuticle (12 for Latronema dyngi sp. nov. vs 20–22 for L. orcinum) and spicule length (65–78 μm for L. dyngi vs 60 for L. orcinum) and shape (weakly arcuate for L. dyngi sp. nov. vs strongly arcuate for L. orcinum). We also performed a maximum likelihood phylogenetic analysis on over 250 nematodes of the subclass Chromadoria based on their nearly full-length 18S rDNA sequences. In agreement with previous studies, our analysis supported Selachinematidae as a monophyletic group and placed Richtersia Steiner, 1916 within Desmodoridae Filipjev, 1922 or just outside of the main Desmodorida clade with the latter placement not well supported.