Paralaxus, Scharhauser & Zimmermann & Gruber-Vodicka & Ott & Leisch, 2020

Scharhauser, Florian, Zimmermann, Judith, Gruber-Vodicka, Harald R., Ott, Jörg A. & Leisch, Nikolaus, 2020, Morphology of obligate ectosymbionts reveals Paralaxus gen. nov.: A new circumtropical genus of marine stilbonematine nematodes, Zoologica Scripta 49 (3), pp. 379-394 : 386

3.4 | Morphological delineation of the genera Paralaxus , Laxus and Leptonemella

Most characters that identify the genus Paralaxus are shared with one or more genera of the Stilbonematinae , but their combination is unique and characteristic. Paralaxus is similar to the genus Laxus %as reflected in the genus name), but also to the genus Leptonemella . The three genera share the extreme forward position of the spiral amphidial fovea, a well-developed cephalic capsule and a gubernaculum without apophysis. Paralaxus can be differentiated from Laxus by the lack of a block layer in the cephalic capsule, the presence of a velum on the male tail and in addition by the presence of a multilayered symbiont coat. Paralaxus shares the lack of the block layer and the presence of a multilayered symbiont coat with Leptonemella , but is distinguished by the greater relative pharynx length b’ %pharynx length/body diameter at end of pharynx), the presence of a velum on the male tail and the lack of sexual dimorphism in the shape of the amphidial fovea.

A special case is L. brevipharynx Armenteros, Ruiz-Abierno , et al. %2014). According to phylogenetic analyses of its 18S and partial COI data %Figure 3a, b), the species belongs to the genus Leptonemella . It is morphologically similar to P. cocos sp. nov., and despite being molecularly a bona-fide Leptonemella , has a short pharynx and no sexual dimorphism in the shape of the amphidial fovea. There are, however, two morphological features, which clearly separate L. brevipharynx from Paralaxus : the lack of a velum on the tip of the tail in males and the lack of the long forward directed cephalic setae characteristic for all Paralaxus species.