Tetranchyroderma anisoankyrum, 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 : 484-486

Tetranchyroderma anisoankyrum sp. nov.

( Fig. 1 )

Type material. Holotype (NIBRIV0000279610) and 15 paratypes (KIOSTG0101–0113, NIBRIV0000279611, NIBRIV0000279612) 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; 1–2 m deep).

Etymology. The proposed specific name, anisoankyrum , is from the Greeks an, meaning ‘not’, isos ‘equal, like’, and ankyra ‘anchor’, which refers to the different cuticular armature of pentancres with central tine longer than others.

Diagnosis. A small Tetranchyroderma with adult length upto 312 µm; pharynx length to 72 µm; with 12 papillae on anterior border of head; a pair of rod-like cephalic tentacles arising from papillary basis; pestle organ absent; cuticular armature of pentancres with central tine longer than the others; 2 pairs of dorsolateral cirratumtype tubes located just behind PhJIn and at mid-intestinal region, respectively; 13–14 lateral cirratum-type tubes per side distributed along whole body length; adhesive tubes: 4 TbA per side; a pair of TbL in mid-trunk region; 13 TbVL per side in intestinal region; foot-type TbV absent; 4 pairs of TbP, forming trifid pedicles with 2 distal tubes and 1 elongate cirratum-type tube, flanked by 1 medial tube; copulatory organ slender pear-shaped.

Description of the holotype. Body small, Lt 255 µm; broad head, both sides nearly parallel in trunk region, narrowing posteriorly; widths of head/neck/PhJIn/trunk/caudal base 57/31/33/39/17µm at U09/U33/U43/U67/U95, respectively.

Head protruding anteriorly with scalloping edge, armed with 12 large papillae on anterior border of oral hood, each bearing 1–2 sensilla at tip, except for two papillae each with short, rod-like cephalic tentacle (7 µm long), at U04. Thirteen short sensory hairs (3–8 µm long) scattered along anterior margin of oral hood, which lacks cuticular armature of pentancres; 22–25 hairs (11–16 µm long) per side aligned dorsolaterally and laterally throughout nearly whole body length (U11–U95).

Epidermal glands, 5–6 per side, with irregular shape and size (4–6 µm in diameter), asymmetrically distributed from anterior pharyngeal region to posterior trunk region at U15–U81.

Cuticular armature with pentancres only ( Fig. 1 C), covering dorsal and lateral surfaces nearly completely, except for most anterior part of oral hood and caudal lobes; with 10–12 columns in mid-trunk region, each column comprising 33–37 ancres; central tine (10 µm long) 1.4–1.7 times longer than the others (7 µm long) in mid-trunk region; ancres 11 µm in diagonal length in most parts of trunk, but smaller on anterior part of oral hood (4 µm in diagonal length) and caudal base (5 µm in diagonal length).

Two pairs of dorsolateral cirratum-type tubes slender, frontal tube (11–14 µm long) located just behind PhJIn (U43) and rear one (16 µm long) at mid-intestinal region (U67). Lateral cirratum-type tubes, 13–14 per side, ranging 11–16 µm long, more or less evenly spaced along whole body length from U20 to U90.

Adhesive tubes: TbA 4 per side, comprising 1 small medial tube, 5 µm long at U16 and 3 ventrolateral tubes forming small arc, 7 µm long at U14 to U15. A pair of TbL (15 µm long), more slender than TbVL, situated behind first dorsolateral cirratum-type tube at U49. TbVL, 13 per side, robust, ranging 9–14 µm long, aligned in intestinal region (U45–U83) densely except for backmost tube behind anus at U90. Foot-type TbV absent. TbP 4 per side, forming a feeble, trifid pedicle with 2 distal tubes (7 µm long) and 1 elongate cirratum-type tube (10 µm long), accompanied by 1 small medial tube (4 µm long).

Ventral ciliation aligned in single column from just behind TbA to caudal base at U17–U95.

Digestive tract: mouth opening broad (51 µm wide), with oral hood extending forward from U0 to U15; pharynx 72 µm long (measured from ventral border of oral opening to PhJIn), pharyngeal pores at U41; intestine broad and narrowing toward posterior end; anus opens at U88.

Reproductive system: simultaneous hermaphrodite; single testis extending behind PhJIn at U54, posterior end bent to copulatory organ. A large ovum (30X45 µm in diameter) located dorsally in mid-intestinal region at U55– U76. Seminal receptacle small, located between ovum and copulatory organ at U78–U80. Copulatory organ slender, pyriform with truncated anterior border, located at U80–U89.

Ecology. Specimens occurred rarely in fine to medium sublittoral sands (1–3 m in depth), often co-occurring together with Tetranchyroderma multicirratum Lee & Chang, 2007 , T. monokerosum Lee & Chang, 2007 , T. megabitubulatum Lee & Chang, 2012 , and Ptychostomella orientalis Lee & Chang, 2003 .

Measurements and variability. Body lengths of 16 adult specimens ranged from 234 to 312 µm (mean 280 µm, SD 24), maximum widths 35–45 µm (14U–16U) when measured in glycerin mount.

The number and arrangement of TbL, TbP and dorsolateral cirratum-type tubes were consistent, while TbVL and lateral cirratum-type tubes were somewhat variable, ranging from 9–18 and 8–16 per side, respectively. Three specimens showed a ‘foot-type’ lateral cirratum-type tube consisting of two tubes confluent at its base only on one side. TbA arrangement was relatively consistent as one medial and three lateral TbA per side, except for two specimens with four lateral TbA on one side.

Taxonomic affinities. Among 42 Tetranchyroderma species currently described with cuticular armature of pentanceres only, T. anisoankyrum sp. nov., in bearing ancres with different length, is allied with T. polyacanthus (Remane, 1927) , T. tanymesatherum Hummon, Todaro, Balsamo & Tongiorgi, 1996 , T. pentaspersus Nicholas & Todaro, 2006 , and T. corallium Hummon, 2011 .

Tetranchyroderma anisoankyrum sp. nov. is most characteristic and easily distinguished from them, for it is the only species that has a pair of rod-like cephalic tentacles on the anterior border of oral hood. Moreover, T. anisoankyrum sp. nov. differs clearly from three of the above four allied species ( T. polyacanthus , T. tanymesatherum and T. pentaspersus ) by the presence of cirratum-type tubes.

Tetranchyroderma polyacanthus and T. tanymesatherum have an extremely long central tine more than two times longer than peripheral tines, 4–5 times and 2–3 times longer, respectively, (cf. the key to the species of Tetranchyroderma in Todaro 2002), whereas 1.4–1.7 times longer in T. anisoankyrum sp. nov.

Tetranchyroderma pentaspersus and T. corallium have a central tine less than two times as in T. anisoankyrum sp. nov. However, the former T. pentaspersus was different from the new species by a large, thin-walled oral hood with a smooth edge, bifid pedicle and lacking TbDL, and the latter T. corallium by truncated head, larger number of TbDL, dorsolateral cirratum-type tube and medial TbP between pedicles and a presence of TbV.

Figures

FIGURE 1. Tetranchyroderma anisoankyrum n. sp. A, habitus, dorsal view; B, habitus, ventral view; C, pentancre. Scale bars = 50 µm (A, B), 10 µm (C).