Four new dendrochirotid holothurians collected from the Seto Inland Sea and the western part of the Sea of Japan, western Japan Author Yamana, Yusuke 0000-0002-8764-5850 Wakayama Prefectural Museum of Natural History, Funo 370 - 1, Kainan, Wakayama 642 - 0001, Japan yamanayusuke 39 @ gmail. com; https: // orcid. org / 0000 - 0002 - 8764 - 5850 yamanayusuke39@gmail.com Author Nakaguchi, Kazumitsu 0000-0001-6715-4133 School of Applied Biological Science, 1 - 4 - 4 Kagamiyama, Higashihiroshima, Hiroshima 739 - 8528, Japan & nakaguchi-kazu 3 @ hiroshima-u. ac. jp; https: // orcid. org / 0000 - 0001 - 6715 - 4133 nakaguchi-kazu3@hiroshima-u.ac.jp Author Yamaguchi, Shuhei 0000-0002-8280-4437 School of Applied Biological Science, 1 - 4 - 4 Kagamiyama, Higashihiroshima, Hiroshima 739 - 8528, Japan & s-yamaguchi @ hiroshima-u. ac. jp; https: // orcid. org / 0000 - 0002 - 8280 - 4437 s-yamaguchi@hiroshima-u.ac.jp Author Katoh, Mikio 0000-0002-2175-7024 School of Applied Biological Science, 1 - 4 - 4 Kagamiyama, Higashihiroshima, Hiroshima 739 - 8528, Japan & katomiki @ hiroshima-u. ac. jp; https: // orcid. org / 0000 - 0002 - 2175 - 7024 katomiki@hiroshima-u.ac.jp Author Ogawa, Akito 0000-0001-8843-8282 Graduate School of Science, The University of Tokyo, 7 - 3 - 1 Hongo, Bunkyo-ku, Tokyo 113 - 0033, Japan akito 1226. biology @ gmail. com; https: // orcid. org / 0000 - 0001 - 8843 - 8282 akito1226.biology@gmail.com Author Ohtsuka, Susumu Takehara Station, Setouchi Field Science Center, Graduate School of Integrated Sciences for Life, Hiroshima University, 5 - 8 - 1 Minatomachi, Takehara, Hiroshima 725 - 0024, Japan text Zootaxa 2021 2021-08-17 5023 1 1 43 journal article 10.11646/zootaxa.5023.1.1 1175-5326 5225372 E759FD85-1904-45A7-9A4D-56815FB9649B Thyone liaoi Yamana, Ogawa & Ohtsuka sp. nov. [Japanese name: Kehada-namako ( Yamana 2016 )] ( Figs 2B , 3B , 5A–H ) Thyone pedata : Liao & Clark 1995: 505–506 , Fig. 307 a, b; Yamana 2016: 7 , Fig. a. non : Thyone pedata Semper, 1867 –8: p 67. (see Remarks) Material examined. Holotype , WMNH-INV-2014-182 (ST- 7 in 2014, 6 November 2014 , anesthetized length 36 mm , width 10 mm , INSD accession number LC547978 , 622 bps, Fig. 2 B-e) . Paratypes : WMNH-INV-2014-183 (ST- 7 in 2014, 6 November 2014 , length 39 mm , width 9 mm , eviscerated, Fig. 2 B-f); WMNH-INV-2014-184 (ST- 7 in 2014, 6 November 2014 , length 34 mm , width 9 mm , Fig. 2 B-g); WMNH-INV-2014-188 (ST- 4 in 2014, 5 November 2014 , anterior half only, length 13 mm , width 5 mm , Fig. 2 B-h). Diagnosis. Bodywall table ossicles with distorted oval or rhomboidal disc and delicate spire, mostly with one pillar formed by fusion of two pillars and spire with 4–6 minute apical spines. Pedicel supporting table ossicles with narrow curved disc with 2–4 large central perforations and 2–8 small distal perforations; spire high, with two (occasionally three) pillars united distally, ending in 2–4 minute processes. FIGURE 5. Scanning electron microscope images of ossicles of Thyone liaoi sp. nov. , ( holotype , A–H, WMNH-INV-2014- 182). A, ossicles of the ventrolateral tentacle; B, the ventrolateral skin of peri-oral; C, the ventrolateral skin of pharynx; D, the ventrolateral introvert skin; E, the pedicel of the abdominal side; F and G, the middle part of the bodywall on the abdominal side, and on the dorsal side, respectively; H, the ventrolateral anal papilla. TABLE 4. Counts and measurements (Mean ± sd μm) of ossicles from four specimens of Thyone liaoi sp. nov.

Plate and rod		Endplate		Rosette		Table (T) and supporting table (ST)
Samplea	Length		Diameter		No. plate hole		Length		Disc length		No. disc hole (T)		Spire (ST)
n	Mean	Range	n	Mean	Range	Mean	Range	n	Mean	Range	n	Mean	Range	Mean	Range	Mean	Range
WMNH-INV-2014-182
Tentacle	30	139 ± 108	36–432	0	0	4	147 ± 100	77–294	19 ± 11	10–35
Peri-oral skin	0	0	25	37±11	23–69	6	104 ± 11	82–112	20 ± 4	15–24
Oesophagus skin	0	0	10	36 ± 5	27–43	0
Introvert skin	0	0	4	47 ± 13	33–62	12	88 ± 11	68–108	17 ± 4	10–23
Pedicels (ventral)	0	5	176 ± 3	172–179	193 ± 14	171–209	0	24	90 ± 6	78–100	37 ± 4	29–45
Bodywall (ventral)	0	0	0	16	86 ± 12	68–109	9 ± 2	5–13
Anal papilla	7	74 ± 10	62–91	0	0	4	63 ± 3	60–67	16 ± 3	13–20
WMNH-INV-2014-183
Tentacle	29	103 ± 72	38–295	0	0	0
Peri-oral skin	0	0	0	17	75 ± 9	64–92	18 ± 5	12–25
Oesophagus skin	0	0	26	27 ± 7	17–44	0
Introvert skin	0	0	13	40 ± 16	22–83	5	74 ± 18	48–95	15 ± 5	11–22
Pedicels (ventral)	0	3	179 ± 12	166–187	161 ± 36	127–198	0	19	90 ± 10	74–103	34 ± 6	19–41
Bodywall (ventral)	0	0	0	28	100 ± 11	81–120	9 ± 2	5–14
Anal papilla	12	67 ± 6	59–77	0	0	14	55 ± 7	45–69	11 ± 2	8–16
WMNH-INV-2014-184
Tentacle	30	108 ± 69	33–268	0	0	0
Peri-oral skin	0	0	27	38 ±1 0	24–59	8	89 ± 13	70–104	15 ± 6	6–23
Oesophagus skin	0	0	26	36 ±10	14–57	0
Introvert skin	0	0	0	16	92 ±13	71–125	15 ± 4	10–22
Pedicels (ventral)	0	7	176 ± 6	164–183	119 ± 20	85–141	0	23	99 ± 8	79–112	32 ± 6	22–45
Bodywall (ventral)	0	0	0	29	112 ± 20	81–161	9 ± 6	4–31
Anal papilla	19	71 ± 15	51–107	0	0	7	76 ± 6	68–86	6 ± 2	4–8
WMNH-INV-2014-188
Tentacle	30	111 ± 76	35–321	0	0	0
Peri-oral skin	0	0	29	38 ± 11	25–74	4	86 ± 25	65–117	21 ±1 0	9–33
Oesophagus skin	0	0	25	34 ± 5	24–43	0
Introvert skin	0	0	0	24	85 ± 14	56–113	19 ± 8	10–35
Pedicels (ventral)	0	3	170 ± 12	160–184	143 ± 42	96–176	0	15	91 ± 8	78–106	38 ± 7	26–51
Bodywall (ventral)	0	0	0	30	107 ± 12	88–135	10 ± 2	7–17
Anal papilla	Amputated

a WMNH-INV: Invertebrate collection of the Wakayama Prefectural Museum of Natural History. Description. Body medium, up to 39 mm long, fusiform, curved, with both ends tapered and turned slightly upwards ( Fig. 2B ); bodywall thin, soft. Color fading upon preservation. Living body color whitish orange. Tentacles 10, arranged in a single circle, two medioventral tentacles smaller than the other eight. Tentacles and introvert transparent in most parts in living animals, and with some dark brown pigmentation. Several rows of villi surrounding oral opening. Oral disk and pharynx of the preserved specimens dark grayish brown and dark purplish brown, respectively. Pedicels long, non-retractile, covering entire body at constant density, lacking in introvert region. Color of pedicels same and slightly deeper than adjacent body. Pedicels becoming gradually smaller toward anterior and posterior from middle portion of body. Ten anal papillae and five anal teeth in radii. After preservation, color denoted above turned more yellowish and whitish than that of living color. Calcareous ring long, cracking of mosaic patterns mostly caused by the damage of material; main radial plates and interradial plates not fragmented in original condition in the several well preserved specimens ( Fig 3B ). Radial elements elongated, with paired, posterior, weakly fragmented prolongations; each with an anterior projection and notch. Interradial elements also long but without posterior prolongations with slight anterior projections; shortest in dorso-lateral elements. Radial plates and interradial plates loosely adherent. One (or rarely two) Polian vesicles in medioventral, single stone canal in mediodorsal position. Well-matured gonad situated in mid-body, in two clumps, one on each side of dorsal mesentery, most tubules not branched. Gonad lacking ossicles. Bodywall ossicles comprising abundant tables ( Fig. 5F, G , Table 4 ), with distorted, oval or rhomboidal disc and delicate spire, mostly with two pillars fusing into one distally, ending in 4–6 minute apical spines. Table disc with 8–16 perforations, most frequently 8–10; central two perforations large, peripheral perforations small. Tentacle ossicles comprising mostly plates of varying size and shape in trunk and branches, also table ossicles in basal parts ( Fig. 5A , Table 4 ). Table ossicles with distorted oval or rhomboidal disc, and high spires with twopillars with mostly 2–3 crossbeams, and 4–8 apical spines. Some table ossicles have oval discs, possessing two larges central perforations and small distal perforations. Plates elongated, with two, large, central perforations and small distal perforations, occasionally developing a rudimentary spire and/or extra layer in central part. Peri-oral skin ossicles comprising mostly rosettes, with tables in part adjoining tentacle bases ( Fig.5B , Table 4 ). Rosettes have granulated, mulberry-like, densely branched in more than one plane branches. Tables with distorted oval or rhomboidal discs, high spires with two-pillars, mostly with 1–3 crossbeams and 4–6 apical spines. Occasionally plates also exist, some with rudimentary spires and/or extra layer in central part. Pharyngeal villi have rosettes with granulated, mulberry-like ( Fig. 5C , Table 4 ). Introvert with tables and mulberry-like rosettes ( Fig. 5D , Table 4 ). Table ossicles with distorted, oval or rhomboidal disc, and low spires of two-pillars, with mostly 1–2 crossbeams, and 4–8 minute apical spines, occasionally with an extra layer in central part. Rosettes with granulated, mulberrylike. Most pedicels with endplate and supporting tables ( Fig. 5E , Table 4 ). Supporting tables with narrow, curved disc, with 2–4 large, central perforations and 2–8 small, distal perforations; spire high, with two (occasionally three) pillars united distally, ending in 2–4 minute processes ( Fig. 5E , Table 4 ). Endplates with holes arranged in three concentric areas, viz. , commarginally-elongated holes near rim, radially-elongated holes in mid-region, and almost circular holes in central area. Anal papillae with small, irregular supporting plates and tables ( Fig. 5H , Table 4 ). Skin around anus with relatively small and simple tables. Remarks. Thyone liaoi sp. nov. was previously reported as a regional form of “ Thyone pedata Semper, 1867 ,” from the Chinese and Japanese waters ( e.g. , Liao & Clark 1995 , Yamana 2016 ), because the bodywall ossicle morphologies (reported in Clark & Rowe 1971 ; Liao & Clark 1995 ; and the present study) of these species resemble each other. However, Semper (1867 –8) plainly stated that the gonadal tubules of this species have needle-shaped ossicles and that the bodywall possesses quite large ossicles. (These ossicle morphologies were not mentioned in Semper 1867 –8, p 67). The presence of such ossicles were not observed in the present new species. From seas worldwide, there are more than 60 nominal species and subspecies in the genus Thyone (65 or 68 species/subspecies nominated in WoRMS 2021b), in which 14 species are presently classified into the Group III (comprising species with both rosettes and tables in the introvert) congeners which had been implied by Deichmann (1930) , Panning (1949) and Pawson & Millar (1981). The present new species also should be involved into this group as 15th species (Table 8). Among the 15 species of Group III, this species have the four identical characters: 1) granulated, mulberry-like small rosettes ( Fig. 5B–D ) are detected from the peri-oral, pharynx, and introvert skin; 2) length (approx. 70–160 µm) of the bodywall table disc ( Fig. 5F, G ) is exceedingly larger than that of the other 14 species (Table 8-2); 3) length (approx. 30–430 µm) of the tentacle ossicles ( Fig. 5A ) is exceedingly larger than that of the other 14 species (Table 8-2); 4) the two-pillared spire of the bodywall table is united one-pillar with 4–6 minute apical spines ( Fig. 5F, G ), but not forming a crown. From these features, this new species is easily distinguished from the 14 species of the Group III and other 24 species of undetectable group of Thyone (Table 8). Distribution. Known from the Gulf of Tonkin , China , depth 55 m ( Liao & Clark 1995 ), and several localities in the Seto Inland Sea, Japan : middle and eastern parts of the Seto Inland Sea, sand bottom, depth 26 m (ST- 4 in 2014); mud bottom, depth 25–27 m (ST- 7 in 2014), and northen part of the Kii Strait, sand bottom, shallow water ( Yamana 2016 ). Etymology. The species named in honor of the famous researcher Dr. Yulin Liao of the Institute of Oceanology, Academia Sinica (IOAS) Qingdao, China , who first reported this species as Thyone pedata . Molecular data comparison. In BLAST searches, the obtained partial COI gene sequence is deeply divergent from all other sequences. A sequence identified as Paelopatides sp. (INSD accession number KX874356 , 80.6% similarity with 100% coverage) was closest (meaningless at generic/family level).