Thyone kyushuensis Yamana, Ogawa & Ohtsuka 2021, sp. nov.
Creators: name: Yamana, Yusuke
name: Nakaguchi, Kazumitsu
name: Yamaguchi, Shuhei
name: Katoh, Mikio
name: Ogawa, Akito
name: Ohtsuka, Susumu
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Holothuroidea
Dendrochirotida
Phyllophoridae
Thyone
Thyone kyushuensis

description: Thyone kyushuensis Yamana, Ogawa & Ohtsuka sp. nov.   
[New Japanese name: Kyushu-kehada-namako]  
(Figs 2C, 3C, 6A–H)  
 Material examined. Holotype, WMNH-INV-2015-2437 (ST- 5 in 2015, anesthetized, length 13 mm, width 4 mm, INSD accession number LC528688, 616bps, Fig 2 C-i). Paratype, NSMT E-12103 (ST- 10 in 2015, eviscerated calcareous ring, length 6 mm, width 2 mm, eviscerated organs only, Fig. 2 C-j).   
 Diagnosis. Bodywall table ossicles with regular oval or rhomboidal disc with undulant margin, high spire without crossbeam, with two pillars united distally, ending in x-shaped crown with 4–6 minute apical teeth on each tip. Pedicel supporting plate ossicles with narrow curved disc with two large central-most perforations and two by standing minute perforations, and 2–6 small distal perforations, without spire. Tentacle ossicles comprising mostly unbranching rods and/or rod-like rosettes, varying in size and shape.   
 Description. Bodywall thin, soft. Living body color whitish-yellow, not altered by fixation/preservation. Tentacles 10, arranged in a single circle, medioventral two tentacles smaller than other eight. Tentacles and introvert mostly transparent in life, partially with light-brown pigmentation, but contracted and yellowish in paratype. One row of short, villi surrounding oral opening. Color of oral periphery, dark grayish brown. Pedicels long, nonretractile, covering entire body at constant density, lacking in introvert region. Color of pedicels same or slightly deeper than adjacent body. Pedicels becoming gradually smaller anteriorly and posteriorly to middle of body. Ten anal papillae and five anal teeth on radii.   
Calcareous ring long, radial and interradial main plates weakly fragmented (Fig. 3C). Radial elements elongated with an anterior projection and anterior notch, and with paired posterior, weakly fragmented prolongations. Interradial elements also long, without posterior prolongations, with anterior projection, shortest in ventro-lateral elements. One Polian vesicle in medioventral, single stone canal in mediodorsal position. Well-matured gonad situated in posterior mid-body, in single clump on dorsal mesentery, tubules not branched. Gonad lacking ossicles.  
Bodywall with only table ossicles (Fig. 6F, G, Table 5); disc oval or rhomboidal with undulant margin, spire high, without crossbeam, with two pillars united distally, ending in x-shaped top with 4–6 minute apical spines on each tip. Table disc with 5–17 perforations, most frequently 9–12, four central perforations slightly larger than peripheral ones.  
Tentacle ossicles mostly unbranching rods and/or rod-like rosettes, clustered in small white spots of trunk and branches, varying in size and shape, also large table ossicles in basal part of tentacle of holotype (Fig. 6A, Table 5). Large tables with circler or oval disc, with two pillars united distally mostly with 1–2 crossbeams and 3–6 apical spines. Table disc with four large central holes and up to 94 smaller, peripheral ones (Fig. 6A, Table 5). Tables not detected in the paratype (Table 5). Rosettes and rods with numerous short branches, with intermediate shapes between rosettes and rods common (Fig. 6A, Table 5). Peri-oral skin ossicles comprising mostly rosettes, and also large tables in parts adjoining tentacle base. Rosettes, with numerous short, occasionally mulberry-like, granulated, branches. Tables with circuler or oval disc, with two pillars united distally (Fig. 6B, Table 5). Pharyngeal villi with small rosettes, with granulated, grape-like branches (Fig. 6C, Table 5). Introvert with large tables and rosettes (Fig. 6D, Table 5). Large table ossicles with distorted oval or rhomboidal disc, with four large central perforations and 30–75 smaller peripheral ones. Rosettes with numerous short branches. These tables have smaller disc length and fewer perforations in paratype than holotype (Table 5).  
 aWMNH-INV: Invertebrate collection of the Wakayama Prefectural Museum of Natural History, NMST-E: Echinoderms collection of National Museum of Nature and Science.   
Pedicels with endplate and supporting plates (Fig. 6E, Table 5). Supporting plates with narrow, curved disc, with two large central perforations, two minute, adjacent ones, and 2–6 small distal ones. Endplate small, with a few, small peripheral perforations in outer rim, followed by a few large perforations in middle that separated by small clusters or pores, and with a central area of medium-sized perforations. (Fig. 6E, Table 5). Anal papilla with irregular supporting plates (Fig. 6H, Table 5). Skin around anus with regular tables.  
 Remarks. This new species is based mostly on one complete specimen; however, it is readily distinguished from most previously described species of Thyone by the peculiar bodywall ossicles: regular tables with x-shaped crowns with 4–6 minute apical spines on each tip. The presence of such table with x-shaped top was also reported in Thyone pohaiensis Liao, 1986 from the Bohai Sea (Bokkai) of China, which the new species resembles both in its ossicles and anatomy. However, T. pohaiensis usually has supporting tables in the pedicels, whereas the new species only has supporting plates lacking a spire. Furthermore, the tentacle ossicles of T. pohaiensis are comprised of rods with flat surfaces, whereas in the new species they are mostly comprised of rods as well as rod-like rosettes. From the feature of tentacle ossicles, paratype (NSMT E-12103) is detected as this new species, although the table ossicles of peri-oral skin and introvert skin are smaller in disc length and lesser in disc perforation number than those of the holotype (Table 5), viz., both species have polyporous large tables in the introvert and tentacles base, but the table disc in T. pohaiensis is up to approximately 80 µm long and has approximately 25 perforations, whereas the table disc in the present new species is up to approximately 100–150 µm long and has up to approximately 35–100 perforations. Although both species resemble one another in body size, they differ in living body color: T. pohaiensis is translucent light red with brownish tentacles with body length 15–18 mm and width 3–4 mm, whereas the present new species is whitish-yellow with body length 13 mm and width 4 mm. However, our complete specimen is only one individual so that the two species can not be differentiated by these external morphology. This new species and T. pohaiensis both live in sandy bottoms; however, they differ from each other in bathymetrical distribution; because of small sample numbers also it must not be decisive, the present new species were collected from the continental shelf, 92 m deep in ST-5 and 72–73 m deep in ST-10, whereas T. pohaiensis was found in the sublittoral zone, the low-tide mark to 8 m deep.   
 Distribution. Known only from two sampling localities of northern islands of off Kyushu Island of western Japan: off Hisaka-shima Island, Goto Islands, Nagasaki Pref., sand bottom, depth 92 m (ST- 5 in 2015), and Genkainada Sea, Fukuoka Pref., sand bottom, depth 72–73 m (ST- 10 in 2015).   
 Etymology. The specific name is an adjective, derived from the locality name of Kyushu Island.   
 Molecular data comparison. In BLAST searches, the closest hit to the COI sequence is from Thyone nigra (INSD accession number KF142163, 82.7% similarity with 93% coverage). The results of BLAST searches supports that the present species belongs to Thyone.
description: Published as part of Yamana, Yusuke, Nakaguchi, Kazumitsu, Yamaguchi, Shuhei, Katoh, Mikio, Ogawa, Akito & Ohtsuka, Susumu, 2021, Four new dendrochirotid holothurians collected from the Seto Inland Sea and the western part of the Sea of Japan, western Japan, pp. 1-43 in Zootaxa 5023 (1) on pages 15-18, DOI: 10.11646/zootaxa.5023.1.1, http://zenodo.org/record/5225372