Neocucumis misakiensis Yamana & Kohtsuka 2018, sp. nov.

Neocucumis misakiensis sp. nov.

[New Japanese name: Kiiro-gumimodoki]

(Figs 1B, 2B, 4A–H)

Material examined. Holotype, WMNH-INV-2016-208 (St. 4, 1 November 2015, length 14 mm, width 5 mm). Paratypes: WMNH-INV- 2015-32 (St. 1, 26 August 2014, length 19 mm, width 9 mm); WMNH-INV- 2015-33 (St.

1, 26 August 2014, length 19 mm, width 7 mm); WMNH-INV-2016-209 (St. 4, 1 November 2015, length 14 mm, width 5 mm); WMNH-INV-2016-214 (St. 1, 25 July 2016, length 16 mm, width 5 mm).

Other material: 5 specimens, WMNH-INV- 2015-27 –31 (St. 1, 26 August 2014, length 12–16 mm, width 6–8 mm); 1 specimen, WMNH-INV-2016-210 (St. 4, 1 November 2015, length 10 mm, width 5 mm); 3 specimens, WMNH-INV-2016-211–213 (St. 1, 25 July 2016, length 15–16 mm, width 4–5 mm); 1 specimen, WMNH-INV- 2017-37 (St. 1, 26 August 2014, length 16 mm, width 5 mm).

Description. Body fusiform, with both ends tapered and turned upwards (Fig. 1B), posteriorly more so; body wall thin, mostly soft, rarely hard. Anus terminal on narrow posterior end. Skin, tentacles, pedicels, and introvert yellow or pale yellow (live coloration) but fading upon preservation. Some specimens extremely swollen, transparent. Tentacles 20, arranged in double circles (10 + 10), five pairs of large interradial tentacles in outer circle and five pairs of smaller radial tentacles in inner circle. Numerous thin, short villi-like projections surrounding oral opening. Five brownish spots in peri-oral skin, adjacent to base of radial tentacles. In addition small brownish spots sometimes occur on tentacles. Pedicels non-retractile or partially retractile, in two rows along each radius throughout body length, each row with approximately 25–45 pedicels, the latter becoming gradually smaller anteriorly and posteriorly, sparse and small on introvert, usually less than 10 in each row. Five anal papillae and five anal teeth in radii.

Radial and interradial elements of calcareous ring solid, unfragmented (Fig. 2B), with posterior bifurcations (prolongations), those of the radial plates longer; central part of radials slightly constricted but that of the interradials slightly expanded. Radial plates in addition with anterior bifurcations, each bifurcation bearing an anterior notch. Interradial plates sharply pointed anteriorly. One long Polian vesicle and one thin stone canal. Gonad in mid-body, in two clumps, one on each side of dorsal mesentery, sometimes tubules with one or two branches.

In body wall, table ossicles abundant (Fig. 4F, G, Table 2), with distorted oval or rhomboidal disc and high spire, mostly with one pillar formed by fusion of two (very rarely, two pillared tables with one cross-beam also present); spire with 2–6 minute processes present in middle to upper part. Table disc with 3–12 perforations, most frequently 8, four large central ones and four smaller marginal ones. Anal papilla with small and irregular supporting plates (Fig. 4H, Table 2). Skin around anus with tables, relatively small and simple. Peri-oral skin with rosettes (Fig. 4B, Table 2).

Ossicles of tentacles comprise plates and rosettes, varying in size and shape (Fig. 4A, Table 2). Pharyngeal villi contain rosettes, long thin rods, and narrow plates (or swollen rods), with distal and often central perforations (Fig. 4C, Table 2). Introvert with only tables (Fig. 4D, Table 2), with oval disc and high two-pillared spire, the pillars joined distally and ending in 4–8 minute processes. Such tables sometimes occur also in basal part of tentacles. Gonad lacking ossicles.

Most pedicels with endplate and supporting tables (Fig. 4E, Table 2). Supporting tables with narrow curved disc with 2–4 large central perforations and 1–5 small distal perforations; spire high, with two pillars united distally, ending in 2–4 minute processes, sometimes 2–4 minute processes also present in middle of spire (Fig. 4E); unusual supporting plates occasionally present in distal tip of pedicel (Table 2).

Remarks. This species has 20 tentacles, a peculiar calcareous ring, pedicels arranged in double rows, and table ossicles in the body wall. This combination of features is typical of the genus Neocucumis Deichmann, 1944. which is represented by two nominal species from Japan, N. sagamiensis (Ohshima, 1915) at 369 fathoms (ca. 675 m) in Sagami Bay and N. watasei (Ohshima, 1915) at 131 fathoms (ca. 240 m) in Suruga Bay. However, both these species have a short calcareous ring which lack posterior bifurcations or prolongations of the radial plates (Ohshima 1915) and have different type of table ossicles. Although N. doelahensis Heding & Panning, 1954, from Kai Islands (Heding & Panning 1954), has similar table ossicles and calcareous ring, its tentacle ossicles are Xshaped rods whereas the combination of the tentacle ossicles of the new species are simple plates and rosettes. The new species also differs significantly from other nominal species of the genus.

Distribution. So far known only from the type locality: off Jyogashima Island, south coast of Kanagawa Prefecture, sand bottom, 84.5– 106 m deep, Pacific Ocean, middle Japan.

Etymology. The specific name misakiensis was derived from the name of peninsula Misaki, near the type locality.