Deraionema, Leduc, 2023

Leduc, Daniel, 2023, New nematode species and genera (Nematoda: Chromadorea) from cold seeps on Hikurangi Margin, New Zealand, European Journal of Taxonomy 856, pp. 1-45 : 22-23

Genus Deraionema gen. nov.

urn:lsid:zoobank.org:act:BF025843-A358-490E-8C22-0CA5B967BF79

Type species

Deraionema barbatum gen. et sp. nov.

Diagnosis

Cuticle finely striated; sixteen longitudinal rows of subcephalic setae posterior to amphids; sexual dimorphism in amphid shape: in males, amphideal fovea and aperture form a single, narrow band (or ‘collar’) around the entire circumference of the cephalic region, presumably resulting from the fusion of the left and right amphids, in females, amphids are transversely oval with faint outline; large conical buccal cavity; male reproductive system with two opposed testes; spicules slender and elongated; gubernaculum without apophyses; conicocylindrical tail with terminal setae.

Differential diagnosis

The new genus differs from all other genera within the Xyalidae , and indeed all genera within the entire phylum Nematoda, in having males with a single annular amphideal fovea and aperture surrounding the entire circumference of the cephalic region. Within the Xyalidae , amphids are most commonly rounded or oval-shaped, or can be spindle-shaped ( Xenolaimus Cobb, 1920 ) or indistinct (e.g., Gnomoxyala Lorenzen, 1977 ). In some genera such as Pseudoechinotheristus Blome, 2002, the oval amphids are transversely elongated and may occupy close to 100% of the corresponding body diameter, but the two amphids always remain distinct. In Deraionema gen. nov., it appears that the two amphids have become so wide as to become fused, thus forming a single structure. In some specimens, it is possible to discern the amphideal nerve extending posteriorly from the amphid, which allows to determine the position of the lateral sectors.

Deraionema gen. nov. is most similar to Paramonohystera Steiner, 1916 in the conical buccal cavity, structure of the copulatory apparatus (i.e., elongated, slender spicules and gubernaculum without apophyses) and conicocylindrical tail with terminal setae. In addition to differences in male amphid shape, the two genera can be differentiated by the presence of 16 longitudinal rows of subcephalic setae in Deraionema gen. nov. (vs absent in Paramonohystera ).

Etymology

The species name is derived from the Greek ʻ deraion ʼ meaning ʻnecklaceʼ, ʻcollarʼ and ʻ nema ʼ meaning ʻthreadʼ, and refers to the shape of the amphids in males.