Tetranchyroderma coreense, 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 : 486-489

Tetranchyroderma coreense sp. nov.

( Fig. 2 )

Type material. Holotype (NIBRIV0000279616) and 12 paratypes (KIOSTG0201–0211, NIBRIV0000279617) mounted in glycerin on H-S slides, 7 Oct. 2001, leg. J. Lee & C. Y. Chang.

Type locality. Hwasun, Jeju Island, Korea (33°14′26″N, 126°19′50″E; 4–5 m deep).

Etymology. The specific name coreense alludes to the type locality of the present new species, Korea.

Diagnosis. A small Tetranchyroderma with adult length upto 382 µm; pharynx length to 92 µm; PhJIn at U42; head large, rounded with its anterior edge uneven; cephalic tentacles and pestle organs absent; cuticular armature of pentancres only; a pair of lateral cirratum-type tubes located at anterior pharyngeal region, 2 pairs of dorsolateral tubes at just behind PhJIn and mid-intestinal region, respectively, and 3–4 pairs of small ventrolateral tubes in intestinal region; adhesive tubes: 8 TbA per side, comprising 1 small medial tube and 7 ventrolateral ones; 2 TbL per side, one situated at behind mid-trunk and another at posterior edge of trunk; 22–23 TbVL per side, anteriormost one behind TbA, 17–18 tubes in intestinal region, 4 tubes behind foot-type TbV to caudal base; a pair of foot-type TbV, each consisting of 4–5 tubes; paired pedicles trifid with 2 distal tubes and 1 elongated dorsal cirratum-type tube, furnished with 9 medial tubes between pedicles; copulatory organ small pear-shaped.

Description of the holotype. Body oblong, Lt 312 µm; a little constricted in pharyngeal region and caudal base; widths of head/neck/PhJIn/trunk/caudal base 70/41/48/52/26 µm at U07/U28/U42/U64/U94, respectively. Head large and rounded, with its anterior margin uneven with 12–15 irregular peaks each bearing 1–2 short, stiff sensilla. Two pairs of sensory hairs located at anterior margin of head, which lacks cuticular armature; 5–6 hairs aligned along lateral body from first lateral cirratum-type tube to caudal base (U21–U94).

Epidermal glands suboval, different in size (4X 6–9X16 µm); more than 30 per side, asymmetrically distributed along nearly whole body length (U09–U92) at subdorsal and lateral sides.

Cuticular armature with pentancres only, arranged in 13–15 columns in mid-trunk region at U59, each column with 27–31 pentancres; covering dorsal and dorsolateral surfaces except for anteriormost part of head and caudum; pentancres 12 µm in diameter in trunk region, but smaller on anterior oral hood (3 µm in diagonal length) and caudal base (4-5 µm in diagonal length); ancres consisting of 4 slightly incurved peripheral tines and 1 straight central tine (7-8 µm long), all similar in length.

Three pairs of lateral cirratum-type tubes, anteriormost tube, 8 µm long, located at anterior pharyngeal region (U21), second one, 8 µm long, at just behind PhJIn (U44), and third one, 8 µm long, at mid-intestinal region (U66), respectively; latter two pairs situated more dorsolaterally; 3–4 small ventrolateral cirratum-type tubes per side irregularly situated along with TbVL in intestinal region at U45–U77.

Adhesive tubes: TbA 8 per side, comprising 1 small medial tube, 5 µm long, and 7 ventrolateral tubes forming a group, 6–8 µm long at U12 to U14. Two pairs of TbL, first tube, 13 µm long, situated at anterior intestinal region (U57) and second one, 15 µm long, at latero-posterior edge of body (U90). TbVL, 22–23 per side; foremost tube small (6 µm long), situated just behind TbA at U18; 17–18 TbVL, 9–13 µm long, distributed densely from PhJIn to posterior intestinal region at U39–U78; 4 tubes far away from TbVL, behind foot-type TbV to caudal base at U87– U93. A pair of foot-type TbV consisting of 4–5 tubes, similar in length, fused at base, located in posterior trunk region at U81. TbP forming trifid pedicle with 2 distal tubes and 1 elongated dorsal cirratum-type tube, furnished with 9 medial tubes between pedicles.

Ventral ciliation arranged in single column from just behind TbA to caudal base (U13–U92).

Digestive tract: mouth opening broad (62 µm wide) with oral hood extending forward from U0 to U13; pharynx 92 µm long, pharyngeal pores at U36; intestine slightly swollen near mid-region and narrowing toward posterior end; anus at U90.

Reproductive system: simultaneous hermaphrodite; testis on right, not reaching to PhJIn at U48; vas deferens with its posterior end slightly bent, approaching to copulatory organ. A large ovum (22X73 µm in diameter) located dorsally in mid-intestinal region at U52–U68. Seminal receptacle spherical, 18X17 µm in diameter, located in front of copulatory organ at U77–U83. Copulatory organ small pear-shaped and truncated anterior border at U83–U89.

Ecology. Specimens occurred rarely in medium sublittoral black volcanic sands (4–5 m in depth), often cooccurring together with T. multicirratum Lee & Chang, 2007 , T. aethesbregmum Lee & Chang, 2012 and Pseudostomella longifurca Lee & Chang, 2002 .

Measurements and variability. Body lengths of 13 adult specimens ranged from 281 to 382 µm (mean 306 µm, SD 13), maximum widths 43–58 µm (14U–18U), when measured in glycerin mount.

Adhesive tubes showed somewhat asymmetrical array depending on individual: numbers of TbA, TbVL, foottype TbV, lateral TbP and medial TbP were somewhat variable, ranging from 7–10, 14–18, 3–5, 3–5 tubes per side and 6–7 tubes, respectively. Ventrolateral cirratum-type tube, its number ranging from 2–5, was too small and difficult to find out among TbVL. Lateral cirratum-type tube was lacking one tube on one side in three specimens; TbL had only an anterior tube on one side in another two specimens.

Taxonomic affinities. In sharing a character combination of complete dorsal covering of pentancres with tines of equal length, presence of cirratum-type Tb(D)L and lack of cephalic tentacles, T. coreense sp. nov. most resembles T. hirtum Luporini, Magagnini & Tongiorgi, 1973 , T. norvegicum Clausen, 1996 and T. xenodactylum Hummon, 2011 .

Among the above three congeneric species, T. coreense sp. nov. is closely similar to T. norvegicum and T. xenodactylum by the presence of three pairs of dorsolateral cirratum-type tubes, paired foot-type TbV and trifid pedicles. However, T. coreense sp. nov. has TbL and ventrolateral cirratum-type adhesive tubes, whereas the two congeners do not have both of them. Furthermore, T. xenodactylum bears sub-cylindrical finger-like structure at the base of the pharynx (Hummon, 2011).

Tetranchyroderma hirtum is discernible from the new species by six pairs of dorsolateral cirratum-type tubes (versus three in T. coreense sp. nov.), 30 evenly distributed TbVL between TbA and caudal base (while 21–23 notevenly spaced TbVL in T. coreense , that is, one at anterior pharyngeal region, 17–18 at intestinal region and 3–4 ones near anus to caudal base, respectively), and absence of TbL and foot-type TbV.

Figures

FIGURE 2. Tetranchyroderma coreense n. sp. A, habitus, dorsal view; B, habitus, ventral view; C, pentancres. Scale bars = 50 µm (A, B), 10 µm (C).