Phanodermopsis dordi Shimada, 2020

Shimada, Daisuke, Takeda, Naoya, Tsune, Akira & Murakami, Chisato, 2020, Three new species of free-living marine nematodes (Nematoda: Enoplida) from the Clarion-Clipperton Fracture Zone (CCFZ), North Pacific, Zootaxa 4859 (4), pp. 507-526 : 510-513

Phanodermopsis dordi Shimada , sp. nov.

Figures 1–2 , Table 4 .

Type material. Holotype. Adult male (NSMT-As 4617), formalin-fixed, permanent whole mount, broken in posterior body region and connected with vas deferens (see Figures 1 , 2 ).

Type locality. CCFZ (10° 25.9376′ N, 147° 50.0029′ W, 5321 m depth) with a spade corer by the third author on 1 Oct. 2016 .

Diagnosis. Phanodermopsis dordi sp. nov. is characterized by the papilliform outer labial and cephalic sensilla, the absence of the sub-cephalic sensilla, the anterior position of the pore of secretory-excretory system (1.4 cephalic diameters from anterior body end), the long, conical tail (2.3 cloacal body diameters) with an acute tip, the long spicules (1.9 cloacal body diameters), and the absence of the gubernaculum.

Etymology. The specific name dordi is a noun in the genitive case after DORD.

Description. Male. Body almost cylindrical, tapering toward both ends. Cuticle finely striated, 2–5 μm thick. Somatic sensilla absent. Gland cells surrounding intestine (cf. Shimada & Kakui 2019) absent. Head rounded and slightly set off by constriction at 0.6 cephalic diameters from anterior body end, diameter at level of cephalic sensilla bases equal to 0.2 maximum body diameters. Cephalic cuticle 1–2 μm thick. Type II pharyngo-cephalic complex (cf. Zograf et al. 2015) present: pharyngeal capsule with three short outgrowths at anterior end; cephalic capsule weakly developed (ca. 1 μm thick and 6 μm long). Six inner labial sensilla papilliform. Six outer labial and four cephalic sensilla also papilliform, arranged in separate circles (the former just anterior to the latter), situated at 0.4 cephalic diameters from anterior end. Sub-cephalic or cervical sensilla absent. Amphids situated at 0.75 cephalic diameters from anterior end, 0.3 corresponding body diameters wide, with transverse slit-like aperture and pocket-like fovea. Buccal cavity conical, without solid teeth. Pharynx enlarged posteriorly. Pore of secretory-excretory system located at 1.4 cephalic diameters or 0.05 pharyngeal lengths from anterior end. Gland cell of secretory-excretory system not observed. Nerve ring at 0.45 pharyngeal lengths from anterior end. Cardia short, 1/3 of corresponding body diameters long. Intestine almost cylindrical, broken in posterior body region. Tail conical, 2.3 cloacal body diameters long. Cloacal or caudal sensilla not observed. Tail tip acute, with spinneret and no terminal setae. Caudal glands precloacal, but probably lost due to injury of posterior body region. Reproductive system diorchic. Testes opposed and outstretched, both located on left side of intestine: anterior testis longer, situated from 53% to 70% of body length; posterior testis situated from 68% to 74% of body length. Sperms globular or spheroid in shape, 3–10 μm in diameter. Vas deferens conspicuous. Spicules equal in size and shape, 1.9 cloacal body diameters long or 0.8 tail lengths, strongly arcuate, without proximal head, distally not acute. Gubernaculum not observed. Precloacal supplement or sensilla absent.

Female. Not found.

Remarks. A male was identified as a member of the genus Phanodermopsis based on the presence of the type II pharyngo-cephalic complex, the short spicule (less than 2.0 cloacal body diameters), and the absence of the precloacal supplement. Phanodermopsis contains only four valid species: P. groenlandica Ditlevsen, 1926 , P. ingrami Mawson, 1958 , P. kohtsukai Shimada & Kakui, 2019 , and P. nana Zograf et al., 2015 ( Zograf et al. 2015; Shimada & Kakui 2019).

Phanodermopsis dordi sp. nov. differs from all the congeners by the papilliform outer labial and cephalic sensilla (vs. setiform, 0.5–1.0 cephalic body diameters long in the congeners); and the position of the pore of secretoryexcretory system (1.4 cephalic diameters from anterior body end in P. dordi sp. nov. vs. 2.8–4.6 in the congeners). Phanodermopsis dordi sp. nov. is also distinguished from P. groenlandica , P. ingrami , and P. nana by the conical tail (vs. conico-cylindrical with the short posterior portion in the latter three species) and from P. kohtsukai by the longer (2.3 cloacal body diameters) tail with acute tip (vs. 1.3 cloacal body diameters long with blunt tip in P. kohtsukai ). In addition, P. dordi sp. nov. differs from P. ingrami by the longer spicules (1.9 cloacal body diameters in P. dordi sp. nov. vs. shorter than 1.0 cloacal body diameters in P. ingrami ), from P. nana by the absence of the gubernaculum (vs. present in P. nana ), and from P. kohtsukai by the absence of the sub-cephalic sensilla (vs. four sub-cephalic setae present in P. kohtsukai ).

The taxonomic key for the species of Phanodermopsis is as follows:

1 Outer labial and cephalic sensilla papilliform................................................... P. dordi sp. nov.

- Outer labial and cephalic sensilla setiform.................................................................. 2 2 Cephalic setae equal to cephalic diameter............................................................. P. nana

- Cephalic setae equal to or shorter than a half of cephalic diameter............................................... 3

3 Tail conical................................................................................. P. kohtsukai

- Tail conico-cylindrical................................................................................. 4

4 Tail ca. 2.5 cloacal or anal body diameters in males, 2.0 in females....................................... P. ingrami

- Tail shorter than 1.5 anal body diameters........................................................ P. groenlandica

Figures

FIGURE 1. Phanodermopsis dordi sp. nov. Holotype male: A, body; B, cervical region; C, head; D, tail with spicules. Scale bars:A, 1 mm; B, 100 μm; C, 10 μm; D, 50 μm.Abbreviations: a.t., anterior testis; c.c., cephalic capsule; c.d., caudal gland; e.p., pore of secretory-excretory system; p.c., pharyngeal capsule; p.t., posterior testis; v.d., vas deferens.

FIGURE 2. Phanodermopsis dordi sp. nov. Holotype male: A, head, outer view with anterior sensilla; B, head, outer view with amphidial aperture; C, head, inner view with pharyngeal and cephalic capsules; D, injured posterior region; E, cloacal and caudal regions; F, right spicule; G, proximal end of left spicule; H, distal end of left spicule; I, sperms in testis. Scale bars: A–C, 5 μm; D, 100 μm; E, F, 20 μm; G–I, 10 μm.Abbreviations: a.a., amphidial aperture; c.c., cephalic capsule; c.s., cephalic sensillum; i.l.s., inner labial sensillum; o.l.s., outer labial sensillum; p.c., pharyngeal capsule.