Tetranchyroderma megabitubulatum, Lee & Chang, 2012

Lee, Jimin & Chang, Cheon Young, 2012, Three new gastrotrich species of the genus Tetranchyroderma (Macrodasyida: Thaumastodermatidae) from Korea, Zootaxa 3368 (1), pp. 245-255 : 249-251

Tetranchyroderma megabitubulatum sp. nov.

( Figs 3 , 5D, E )

Type material. Holotype (DBG1901) and 12 paratypes (DBG1902–1910, NIBRIV0000245096, 0000245097) mounted in glycerin on H-S slides, 29 June 2006, leg. J. Lee.

Type locality. Baegripo Beach , Taean, Korea, 36°48'43"N 126°09'14"E, 1–3 m deep .

Etymology. The proposed specific name megabitubulatum alludes to a pair of large dorsolateral adhesive tubes.

Diagnosis. A small Tetranchyroderma an adult length to 464 µm; pharynx length to 100 µm; with fanwise head and slender body; armed with two pairs of rod-like cephalic tentacles and a pair of pestle organs; cuticular armature consisting of pentancres only; adhesive tubes: an oblique row of three TbA per side, comprising a medial and two ventrolateral tubes; a pair of long TbDL in mid-intestinal region; 14–15 TbVL per side, foremost tube located in anterior pharyngeal region and 13–14 TbVL in intestinal region; a pair of foot-type TbV consisting of two tubes; 5–7 TbP per side, forming trifid pedicles with two distal tubes and a dorsal cirratum, flanked by a medial and 2–3 lateral tubes.

Description of holotype. Body ( Fig. 3A, B ) slender and elongate, arched dorsally, flattened ventrally, 353 µm long; bothsides more and less parallel, except for a slight constriction in posterior pharyngeal region and caudal base; caudal pedicle elongate; widths of head/neck/PhJIn/trunk/caudal base 57/25/28/32/17 µm at U6/U27/U34/ U60/U93, respectively.

Head broad and fanwise with 15 sensory hairs scattered on dorsal surface of oral hood; anterior margin convex and uneven, with seven peaks, each peak bearing 2–3 papillae with sensory hairs. Two pairs of rod-like cephalic tentacles present; first pair slender and long, 15 µm long, situated on anterolateral peak of oral hood at U2; second pair short, 10 µm, situated slightly dorsally just behind the preceding one at U3. A pair of pestle organs situated at posterolateral corner of head, beside ventrolateralmost TbA at U10, protruding ventrolaterally, each accompanied by two short hairs. Numerous paired sensory hairs (~17 µm long) dorsolateral and lateral surfaces behind pestle organ to middle of caudum (U12).

Epidermal glands of granular type, six per side, asymmetrically distributed from U21 to U86, with different size (4–7 µm in diameter).

Cuticular armature ( Figs. 3C , 5E ) with pentancres only, scattered all over dorsal surface excluding anteriormost part of oral hood and caudum; arranged in 13–15 columns in mid-trunk region (U53), each column with up to 50–55 pentancres; ancres with slender tines, 3 µm in diagonal length on head, 4 µm on caudal base, and 16 µm in mid-trunk region.

Adhesive tubes: three TbA per side arranged obliquely, consisting of a small medial tube, 8 µm long, pointing backward at U12 and two ventrolateral tubes, 13 µm and 9 µm long, U11 and U10, respectively; a pair of elongated TbDL ( Fig. 5D ), 57 µm long, situated in middle of intestinal region at U62; 14–15 TbVL per side, foremost tube 9 µm long, at U16, others more robust, from 9 µm in length, distributed intestinal region U36 to U78; paired foottype TbV represented by two tubes at posterior intestinal region at U81, medial tube shorter than lateral tube, 9 µm and 15 µm long, respectively; 6–7 TbP per side, forming a little elongated pedicle with three tubes, two horizontal tubes and a dorsal, cirratum-type tube, 8 µm long; flanked by a medial tube (10 µm long) and 2–3 lateral tubes, of which the latter extends to the anus at U89.

Ventral ciliation aligned in a single column from just behind TbA to the anus (U13–U92).

Digestive tract: oral opening broad (52 µm wide) with oral hood extending forward above the mouth from U0 to U10; pharynx 85 µm long, narrows to half of posterior part at U23-U34; a pair of pharyngeal pores opens laterally, slightly in front of PhJIn at U32; intestine broad with both ends narrowing a little; anus opens ventrally at U89.

Reproductive system: simultaneous hermaphrodite; single testis on right side, extending far behind, at U47. A large ovum (20X56 µm in diameter) located dorsally in midtrunk region at U52–U68. Seminal receptacle between ovum and copulatory organ at U67–U78, elongated, ellipsoidal, 41 µm long, containing several spermatozoa. Copulatory organ elongated, protruding anteriorly, 39 µm long (U77–U94).

Ecology. Specimens occurred in low abundance in fine to medium sublittoral sands (1–3 m in depth), often together with Tetranchyroderma multicirratum Lee & Chang, 2007 and Ptychostomella orientalis Lee & Chang, 2003 .

Measurements and variability. Body lengths of 12 type specimens mounted in glycerin range from 316 to 464 µm (mean 388 µm, standard deviation 39), maximum widths from 29–39 µm.

Number and arrangement of adhesive tubes show some variation. Two specimens have an additional ventrolateral TbA on one side. Foot-type TbV usually consists of two tubes, except for four specimens with three tubes on one side only. Single TbVL is present in the pharyngeal region consistently, but the number of tubes in the intestinal region is rather variable, 13–20 per side, asymmetrically distributed. TbP usually form a trifid pedicle flanking a medial tube, however, the number of lateral tubes are variable, ranging from 2 to 4 per side .

Taxonomic affinities. Among the allied congeners with cuticular armature of pentancres only, T. megabitubulatum sp. nov. is most similar to T. quadritentaculatum Todaro, Balsamo & Tongiorgi, 1992 in having two pairs of cephalic tentacles and a pair of TbDL. However, T. megabitubulatum sp. nov. is clearly distinguished from this species by the presence of pestle organs, a pair of TbV, a TbVL in the anterior pharyngeal region, much longer TbDL in the mid-intestinal region, and the fanwise shape of head (compared to a truncated anterior margin of the head in T. quadritentaculatum ).

In the genus Tetranchyroderma , T. megabitubulatum sp. nov. shares two pairs of cephalic tentacles and pestle organs only with T. multicirratum Lee & Chang, 2007 from Korea. It is easily distinguished from T. multicirratum by a larger body size (353 µm in T. megabitubulatum versus 227 µm in T. multicirratum ), absence of cirratum-type tubes, and a different composition of cephalic tentacles (consisting of two rod-like tentacles in T. megabitubulatum , while a rod-like tentalcle and a conical tentacle are present in T. multicirratum ).

Figures

FIGURE 3. Tetranchyroderma tritentaculatum sp. nov. A, habitus, dorsal view; B, habitus, ventral view; C, pentancres. Scale bars = 50 µm (A, B), 10 µm (C).

FIGURE 5. A–C, Tetranchyroderma aethesbregmum sp. nov.: A, head, dorsal view, DIC micrograph; B, head, frontal view, SEM micrograph; C, pentancres, SEM micrograph. D–E, Tetranchyroderma tritentaculatum sp. nov., SEM micrographs: D, mid-intestinal region showing a pair of dorsal adhesive tubes; E, pentancres. F, Tetranchyroderma insolitum sp. nov., cuticular armature with tetrancres and triancres mixed, SEM micrograph. Scale bars = 10 µm (A, B, D), 5 µm (C, E, F).