Tetranchyroderma insolitum, 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 : 252-255

Tetranchyroderma insolitum sp. nov.

( Figs 4 , 5F )

Type material. Holotype (DBG1801) and four paratypes (DBG1802, 1803, NIBRIV0000245098, 0000245099) mounted in glycerin on H-S slides, 8 May 2009, leg. J. Lee and C.Y. Chang.

Type locality. Myeongsasipri Beach , Sinjido Island, off Wando Island, Korea, 34°19'35"N 126°48'34"E, 1–3 m deep .

Additional material examined. Ten individuals mounted in glycerin, Myeongsasipri Beach, Sinjido Is.,Wando Is., 8 Feb. 2003, leg. J. Lee and C.Y. Chang; eight individuals in glycerin, Gasa Beach, Joyakdo Island, 15 Nov. 2010, leg. J. Lee and C.Y. Chang.

Etymology. The specific name, insolitum , is derived from the Latin insolitus, meaning “strange, odd, unusual, peculiar”, which alludes to the unusual cuticular armature with both triancres and tetrancres and peculiar earlobelike protrusions at ral corners head.

Diagnosis. A small Tetranchyroderma an adult length to 389 µm; pharynx length to 101 µm; with round anterior border of head and an earlobe-like protrusion at each posterolateral corner the head; cephalic tentacles absent; with combined cuticular armature consisting of tetrancres and triancres; four dorsolateral cirratum-type tubes and six lateral cirrata per side; four TbA per side; 6–18 TbVL per side; a pair of foot-type TbV, each consisting of two tubes with different lengths; a pair of pedicles, trifid with two distal tubes and a dorsal cirratumtype tube, accompanied with 2–4 medial and three lateral tubes; copulatory organ pyriform.

Description of holotype. Body ( Fig. 4A, B ) oblong and slender, Lt 320 µm, vaulted dorsally, flattened ventrally; pharyngeal region slightly slender, and both sides nearly parallel; caudal pedicle elongate and naked; widths of head/neck/PhJIn/trunk/caudal base 44/31/34/41/25 µm at U5/U22/U36/U54/U92, respectively.

Head broad with gently convex anterior border; a pair of drooping, earlobe - like protrusions (not pestle organs), present at posterolateral corner of head (U8) with a short hair at each tip; without cephalic tentacles;18 sensory hairs (11–13 µm) implanted along anterodorsal border of oral hood, where are ancres lacking; shorter hairs (3–5 µm) surrounding mouth opening; numerous hairs (13–20 µm) aligned dorsolaterally and laterally at U12–U93.

Epidermal glands: 7–8 per side, beginning at U25 and ending at U91; generally oval, mixed in size (4X5–8X17 µm); a few small gland openings (2 µm in diameter) occurred on dorso- and ventrolateral surfaces, irregularly.

Cuticular armature ( Figs. 4C, D , 5F ) with numerous tetrancres and a small proportion of interspersed triancres, densely covering dorsal, lateral and ventrolateral surfaces; arranged in 14–17 columns in mid - intestinal region, each column with up to 43–48 ancres; anterior and mid-dorsal surfaces of trunk with tetrancres only; remaining surfaces from dorsolateral to ventrolateral and posterior part of trunk mixed with tetrancres and triancres; tetrancres ( Fig. 4C ), 14 µm in diagonal length between opposite tines at mid-trunk region, a little smaller at anteriormost part of head (7 µm) and caudal base (6 µm); triancres ( Fig. 4D ), one side of triangles ca. 6 µm long, at posterior part of trunk region (U84), each tine arising from its own base; triancres distributed irregularly and rarely.

Dorsolateral cirratum-type tubes four per side, slender, containing fine granules; more or less evenly spaced from U17 to U61, with foremost cirratum (12 µm long) in pharyngeal region at U17, and three cirrata from PhJIn to middle of intestinal region (15 µm, 10 µm, and 17 µm long) at U36, U46 and U61, respectively; third cirratum a little shorter, located more dorsally. Lateral cirrata six per side, 7–10 µm long, distributed from just ahead of PhJIn to posterior trunk region at U31–U79.

Adhesive tubes: TbA four per side, forming a feeble arc with a pair of subconical medial tubes (5 µm) and three ventrolateral tubes (6 µm) behind oral opening; a pair of foot-type TbV consisting of two tubes with different lengths (outer one usually much longer), fused at base, situated at posterior trunk region (U81 and U84), asymmetrically distributed; TbVL 16–18 per side, foremost tube (7 µm) located in anterior pharyngeal region at U13, remaining ones much larger, ranging from 9 µm to 23 µm in length, distributed from PhJIn to front of TbV at U32–U76; TbP, eight tubes on right side, 10 on left, forming little elongated pedicles (23 µm), each with two distal tubes and a shorter dorsal cirratum (6 µm) between them, pedicles flanked by 2–4 medial (6–8 µm)and three lateral tubes (6–9 µm).

Ventral cilia covering mid-ventral surface entirely, just behind TbA to base of caudum at U9–U92.

Digestive tract: oral opening broad (36 µm wide) with oral hood extending forward above the mouth from U0 to U07; pharynx 87 µm long, with paired pharyngeal pores opened at U31; intestine narrow and gradually broad toward posterior end; anus opens ventrally at U91.

Reproductive system ( Fig. 5A ): simultaneous hermaphrodite; single testis on right side in dorsal view, extending to behind PhJIn at U39. Vas deferens extending straight with its posterior end slightly bent, approaching to rear of copulatory organ. A well-developed ovum (25X80 µm in diameter) and a small oocyte (6X7 µm in diameter) situated dorsally at mid-trunk (U48–U74). Seminal receptacle ovoid, 15 µm in diameter, located between ovum and copulatory organ at U72–U77. Copulatory organ pyriform, anterior portion broad and gradually narrowing posteriorly, located at U76–U87.

Ecology. Specimens were collected among fine to medium sublittoral sands, from 1–3 m.

Measurements and variability. Body lengths of five type specimens and 18 additional specimens mounted in glycerin range from 255–389 µm (mean 325 µm, standard deviation 36) with maximum widths from 28 µm (9U–14U).

The number and arrangement of dorsolateral and lateral cirrata, TbA, TbVL, and TbP show some variability, ranging from 3 to 5 dorsolateral cirrata, 3–7 lateral ones, 3–4 TbA, 12–18 TbVL, and 6–10 TbP per side, respectively. However, medial TbA, anteriormost TbVL at pharyngeal region, the number and arrangement of TbV, and trifid pedicle are consistent.

Taxonomic affinities. Three species, T. paradoxum Thane-Fenchel, 1970 , T. paralittoralis Rao, 1991 , and T. tentaculatum Rao, 1993 , are known to have a mixed cuticular armature with tetrancres and pentancres. Tetranchyroderma insolitum sp. nov. is most characteristic in having an unusual combination of cuticular armature, consisting of triancres and tetrancres. This type of armature is the first case in the genus to our knowledge. Moreover, T. insolitum sp. nov. is the only species in the genus bearing peculiar drooping earlobe-like protrusions posterolateral corners of head, which are apparently different from pestle organs.

Figures

FIGURE 4. Tetranchyroderma insolitum sp. nov. A, habitus, dorsal view; B, habitus, ventral view; C, tetrancre; D, triancre. Scale bars = 50 µm (A, B), 10 µm (C, D).

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).