Sylphodorylaimus, Nasir & Gholamreza & Faegheh & Abootalebi, 2024

Nasir, Reyes Peña-Santiago, Gholamreza, Nasir Vazifeh, Faegheh, Gholamreza Niknam & Abootalebi, Faegheh, 2024, New insights into the evolutionary relationships of Opisthodorylaimus sylphoides (Williams, 1959), with proposal of Sylphodorylaimus n. gen. (Nematoda, Dorylaimida, Thornenematidae), Zoosystema 46 (15), pp. 349-359 : 351

Sylphodorylaimus n. gen.

urn:lsid:zoobank.org:act:72A0756B-A661-4CC2-9304-80D6EE9F5024

DIAGNOSIS. — Thornenematidae , Thornenematinae. Medium-sized nematodes, 1.66-2.48 mm long. Cuticle dorylaimid. Lip region continuous with the adjoining body, with totally amalgamated lips, and lacking both labial and postlabial sclerotization. Amphid fovea cup-like, its aperture c. one-half of lip region diameter. Cheilostom with moderately thick, inward curved walls. Odontostyle hardly longer than lip region diameter, with aperture occupying one-third to two-fifths of its length. Guiding ring double. Odontophore rod-like. Pharynx entirely muscular, gradually enlarging into the basal expansion that occupies less than half of the total neck length. Female genital system mono-opistho-ovarian, with drastically reduced anterior branch, very weak pars refringens vaginae and short, longitudinal vulva. Tail similar in both sexes, long and filiform. Spicules dorylaimid. Nine to eleven shortly spaced ventromedian supplements with hiatus.

ETYMOLOGY. — The generic substantive is a combination of the type species name sylphoides , and Dorylaimus , the type genus of the order Dorylaimida .

TYPE AND ONLY SPECIES. — Dorylaimus sylphoides Williams, 1959 .

SEPARATION FROM OTHER SIMILAR GENERA

Within Thornenematidae , the new genus shares the lack of sexual dimorphism in tail shape with the genera Indodorylaimus Ali & Prabha, 1974 and Sicaguttur Siddiqi, 1971 , but it differs from these in the absence (vs presence) of a strongly developed cephalic framework, with conspicuous labial and postlabial sclerotization, a significant difference indeed. Besides, Indodorylaimus males have much less (1- 4) ventromedian supplements, whereas Sicaguttur females are di-ovarian.

Sylphodorylaimus n. gen. resembles some members of Dorylaimidae , for instance, a few Prodorylaimus species, in several aspects (continuous lip region with amalgamated lips, relatively strong odontostyle, both sexes with long tail), but it can be easily distinguished from them in its mono-ovarian (vs always di-ovarian) condition.

The proposal of the new genus raises a doubt about the identity of monosexual species of Opisthodorylaimus . Taking into account that females of these species appreciably differ (see below) from those of S. sylphoides n. comb., they are provisionally retained under Opisthodorylaimus until new evidence is available.

Sen et al. (2012) described two new Indodorylaimus species from India, namely I. asaccatus and I. baqrii , with ( Sen et al. 2012: 12) “moderately sclerotized” lip region and no male, among other traits. The true identity of these two species is however questionable as their poor original descriptions, including laconic drawings and pictures, lack enough information. Assuming that labial and postlabial sclerotization may be absent in these species –as suggested by illustrations –, S. sylphoides n. comb. resembles these two taxa in its general aspect, but it can easily distinguished from them by its longer body (1.66-2.48 vs 1.38-1.73 mm in I. asaccatus and 1.40- 1.58 mm in I. baqrii ), longitudinal (vs transverse) vulva, much longer female tail (338-458 vs 233-257 and 155-257 Μm), and male present (vs absent).