Tetranchyroderma oblongum, Lee, Jimin, Kim, Dongsung & Chang, Cheon Young, 2013

Lee, Jimin, Kim, Dongsung & Chang, Cheon Young, 2013, Description of three new Tetranchyroderma gastrotrichs (Macrodasyida: Thaumastodermatidae) from South Korea, Zootaxa 3709 (5), pp. 483-493 : 489-491

Tetranchyroderma oblongum sp. nov.

( Fig. 3 )

Type material. Holotype (NIBRIV0000279618) and 7 paratypes (KIOSTG0301–0306, NIBRIV0000279619) mounted in glycerin on H-S slides, 24 Aug. 2011, leg. J. Lee.

Type locality. Yeonji-ri, Uljin, Korea (37°00′18″N, 129°25′06″E; 5–7 m deep).

Etymology. The proposed name, oblongum , is from the Latin oblongus, meaning ‘longer than broad, oblong’ and refers to the oblong body shape.

Diagnosis. A slender Tetranchyroderma with adult length to 413 µm; pharynx length to 101 µm; head round without cephalic tentacles; cuticular armature of tetrancres only; 7 dorsolateral cirratum-type tubes and 7–9 lateral ones per side, more or less evenly spaced along nearly whole body; adhesive tubes: 7–8 TbA per side; 33–38 TbVL per side situated behind TbA to caudal base; paired pedicles trifid with 2 distal tubes and 1 dorsal cirratum-type tube, flanked by 3 medial tubes and 3 lateral ones; copulatory organ pyriform.

Description of the holotype. Body slender and oblong, Lt 413 µm; both sides nearly parallel in trunk region except for pharyngeal region a little constricted; widths of head/neck/PhJIn/trunk/caudal base 62/42/44/53/36 µm at U05/U20/U33/U54/U95, respectively.

Head rounded, with more than 33 hairs on anterior margin of oral hood at U0–U03. Sensory hairs comprising 12–13 dorsolateral and 15–17 lateral hairs per side, more or less evenly spaced, from anterior head to caudal base at U08–U95 and U10–U93, respectively. Cephalic tentacles absent.

Dorsolateral epidermal glands 9–11 per side, generally oval-shaped, different in size (5–12 µm in diameter), asymmetrically arranged from mid-pharyngeal region to posterior trunk region at U18–U90; 2 glands gathered dorsally between ovum and seminal receptacle; 7 gland openings (stomata) per side, with cuticularized lips, scattered on dorsolateral surface near glands at U22–U97.

Cuticular armature adorned with tetrancres on dorsal and lateral surfaces completely except for anterior part of oral hood at U0–U03; with 18–22 columns in mid-trunk region, each column comprising about 65–69 ancres; each tine of tetrancres similar in length; ancres 10 µm long in diagonal length between opposite tines at mid-trunk region, but smaller on both anterior part of oral hood and caudal base.

Cirratum-type tubes consisting of 7 dorsolateral and 7–9 lateral tubes per side, more or less evenly spaced along nearly whole body at U13–U84 and U21–U92, respectively; dorsolateral cirratum-type tubes (11–13 µm long) larger than lateral ones (4–11 µm long); both dorsolateral and lateral cirratum-type tubes with foremost 2 tubes in pharyngeal region and others from PhJIn to posterior intestinal region.

Adhesive tubes: TbA 7–8 per side, forming a transverse row with anteriormost 8–9 tubes behind mouth opening and a ventrolateral arc with 3–4 tubes. TbVL 33–38 per side, comprising 4–6 tubes, 11–16 µm long, in pharyngeal region and remaining ones longer, with different in size (12–24 µm long) from PhJIn to caudal base, more densely issuing toward caudal base. A pair of trifid pedicles with 2 distal TbP and 1 dorsal cirratum-type tube, accompanied by 3 medial TbP and 3 lateral ones; with a little concave edge between pedicles.

Ventral ciliation covering entire mid-ventral surface, just behind TbA to caudal base at U11–U95.

Digestive tract: mouth opening broad (62 µm wide), as wide as oral hood; oral hood extending forward above mouth from U0 to U09; pharynx 101 µm long, with paired pharyngeal pores opened at U30; intestine straight; anus situated at U93.

Reproductive system: simultaneous hermaphrodite; single testis on right side, extending behind PhJIn at U39. Vas deferens approaching to rear of copulatory organ. A well-developed ovum (35X 50 µm in diameter) followed with 2 small oocytes situated dorsally in mid-intestinal region. Seminal receptacle small, ovoid, 14 µm in diameter, located between ovum and copulatory organ at U78–U82, containing a few spermatozoa. Copulatory organ inverted pyriform, located at U84–U92.

Ecology. Specimens occurred rarely in fine to medium sublittoral sediments (5–7 m in depth).

Measurements and variability. Body lengths of eight adult specimens ranged from 317 to 413 µm (mean 350 µm, SD 31), maximum widths 44–58 µm (13U–18U) when measured in glycerin mount.

The number and arrangement of adhesive tubes were somewhat variable and asymmetrically arranged, 6–9 TbA, 20–38 TbVL, 2–4 medial TbP, and 2–3 lateral TbP per side, respectively. The dorsolateral and lateral cirratum-type tubes ranged 5–8 and 6–11 tubes per side, respectively. Moreover, two specimens had an additional cirratum-type tube near anteriormost one at the anterior pharyngeal region on one side.

Taxonomic affinities. Among the congeneric species with complete dorsal covering with tetrancres only, T. oblongum sp. nov. closely resembles T. cirrophorum Lévi, 1950 and T. verum Wilke, 1954 in sharing the absence of cephalic tentacles (or sensorial organs) and TbV, and the presence of single-lobed head and more than two pairs of TbDL (cf. the key to the species of Tetranchyroderma by Todaro 2002). However, T. oblongum sp. nov. is clearly distinguished from them by the presence of lateral cirratum-type tubes along the body. Besides, T. verum has four pairs of TbDL restricted to the intestinal region.

Figures

FIGURE 3. Tetranchyroderma oblongum n. sp. A, habitus, dorsal view; B, habitus, ventral view; C, tetrancres. Scale bars = 50 µm (A, B), 10 µm (C).