Scoliorhapis stepanovi Smirnov & Panina & Sanamyan & Sanamyan 2017

Scoliorhapis stepaNovi Al. Smirnov and Panina sp. nov.

Fig. 1, A–G, I; Fig. 2; Fig. 3, A–C; Fig. 4 (map); key.

Taeniogyrinae gen. sp.— Stepanov et al., 2012: 15, fig. 1, 2.

Material examined. Holotype— 13.09.2010, East Kamchatka, Avacha Bay, Is. Starichkov, 52.7793, 158.6225, depth 10–11 m, bottom—boulders, stones, muddy gravel with shells, bottom temperature 6°C, diving collection by Sanamyan NP, ZIN No. 1/23624.

Paratypes— 7 specimens, collected together with holotype, ZIN No. 2/23625.

Other investigated samples— 11.09.2008, East Kamchatka, Avacha Bay, Viluchinskaya Bay, La Pérouse Stones, [52.6160, 158.5055], 20 m, sand sample, t 13°C, diving collection by Sanamyan NP, 1 specimen; 18.10.2008, East Kamchatka, Avacha Bay, Is. Starichkov, 52.7727, 158.6154, 21–23 m, t 6°C, diving collection by Sanamyan NP, 1 specimen; 18.07.2010, East Kamchatka, Avacha Bay, Viluchinskaya Bay, La Pérouse Stones, 52.6160, 158.5055, 10 m, sand with shells, boulders, t 9°C, diving collection by Sanamyan NP, 1 specimen; 13.09.2010, East Kamchatka, Avacha Bay, Is. Starichkov, 52.7793, 158.6225, 10–11 m, muddy gravel, stones, boulders, diving collection by Sanamyan NP, 1 specimen; 13.09.2010, East Kamchatka, Avacha Bay, Is. Starichkov, 52.7746, 158.6115, 20 m, gravel with shells, stones, boulders, t 1°C, diving collection by Sanamyan NP, 1 specimen; 26.09.2010, East Kamchatka, Avacha Bay, Is. Starichkov, 52.7737, 158.6198, 24 m, gravel and sand with shells, stones, boulders, t 8°C, diving collection by Sanamyan NP, 1 specimen; 21.07.2011, East Kamchatka, Is. Starichkov, 52.7747, 158.7108, 24 m, sand with shells, stones, boulders, rock, t 2°C, sand sample, diving collection by Sanamyan NP, 1 specimen; 16.07.2014, East Kamchatka, Avacha Bay, Listvinichnaya Bay, Pyramidny Cape, 52.3814, 158.5737, 21 m, sand, boulders, rocks, t 1°C, diving collection by Sanamyan NP, 1 specimen; 06.07.1955, North Kurile Is., Is. Paramushir, Sea of Okhotsk shore, Shelikhovo, coll. Khlebovich VV., 2 specimens; 20.08.16, Middle Kurile Is., Is. Matua, Cape Crocodile, 15 m, t 3°C, diving collection by Sanamyan NP, 2 specimens.

Diagnosis. Scoliorhapis species with 10 peltate-digitate tentacles with up to 5 pairs of narrow elongate digits. Calcareous ring bead-like, with 10 segments; medioventral Polian vessel single, large, connected to ring vessel by narrow duct. Intestine without loop, attached for most of its length by mediodorsal mesentery. Rectal intestine fixed by two mesenteries: mediodorsal mesentery fixed to body wall near right dorsal muscle band, and left ventral mesentery fixed in left ventral interradius near medioventral muscle band. Two series of ciliated funnels: near the middorsal mesentery and in the left dorsal interradius near left ventral radial muscle. Body wall with scattered twopointed sigmoids only, 80–115 µ m in length. Tentacles with straight or C-like rods, sometimes branched at the ends, 70–90 µ m in length.

Description. Body wormlike, cylindrical, slightly tapering to posterior end, up to 50 mm in length. Color in life pink-orange (Fig. 1F), whitish after fixation. Body wall with crowded small warts when compressed, thin and translucent when stretched, when internal organs easily seen (Fig. 1D). Body wall sigmoids noticeable in reflected light (Fig. 1A, C). Ten peltate-digitate tentacles with up to five pairs of narrow elongated comparatively large to tentacle size digits (Fig. 1E). Terminal digits longest. Juveniles terminating with single pair of digits on the tip (Fig. 1G, I). Intestine without loop (Fig. 1D), attached for most of its length by the mediodorsal mesentery in the middle of the interradius. Rectal intestine is approximately 1/5 length of the entire elementary canal length, fixed by two mesenteries: mediodorsal fixed to body wall near right dorsal muscle band and left ventral fixed in left ventral interradius near medioventral muscle band. Two series of crowded ciliated funnels: near middorsal mesentery and in left dorsal interradius near left edge of left ventral radial muscle. Funnels situated singly, wide funnel with thin collar and narrow stalk that is ~ 1.5 times longer than height of funnel (Fig. 3B).

Single, very large, ovoid, midventral Polian vessel connected to water ring by thin short duct (Fig. 3A).

The gonad is slightly branched.

Calcareous ring bead-like, with 10 segments; comparatively small relative to local body width (Fig. 1A, B, D, G, I).

Body wall ossicles two-pointed sigmoids, 80 – 115 µ m in length, scattered throughout body wall, slightly more abundant over muscle bands. Sigmoids are oriented at an angle to longitudinal body axis (Fig. 1A, C). Sigmoid bodies end in hooks on both end, oriented perpendicular to each other. The second hook is likely derived from the eye-like ending of sigmoid hooks in resembles species. The majority of the sigmoids are “sinistral” (Fig. 2A–H) but a few are “dextral” (Fig. 2).Tentacles with straight or C-shaped rods, some with slightly branched, 70 – 90 µ m in length (Fig. 2J, K; 3C).

Distribution. East Kamchatka, Avacha Bay, at 10 – 24 m depth, on sand bottom with bottom temperature 1 – 13°C, in North Kurile Is., Paramushir Is., Sea of Okhotsk shore, Shelikhovo, and in Middle Kurile Is., Matua Is. at 15 m depth (Fig. 4).

Remarks. The main character separating S. stepanovi from other Scoliorhapis species is the shape of the sigmoids that are pointed at both ends. All other species have sigmoid hooks with a point on one end and open-eye on the other. The new species differs from the genotype, S. theeli by the arrangement of the sigmoids in the body wall—scattered in S. stepanovi and clustered in papillae in S. theeli (Théel, 1868 Pl. 2, fig. 3; Heding, 1928, Fig. 69, 1 – 2) (Fig. 3F).

The new species resembles S. lindbergi (see Djakonov et al., 1958; Oguro, 1961; 1965; Levin, 1982; Inoue & Kajihara, 2012). These species share the following characters: similar arrangement and orientation of body wall ossicles (cf. Fig. 1E, I in S. stepanovi and Oguro, 1961, Fig. 2 in S. lindbergi); tentacles with narrow elongated and comparatively large to tentacle size digits (cf. Fig. 1 F in S. stepanovi and Fig. 3E and Inoue, Kajihara, 2012, Fig. 1B, C in S. lindbergi); intestine with rectal part fixed to same mesenteries; large ovoid midventral Polian vessel connected with the water ring by narrow short duct (cf. Fig. 3A in S. stepanovi and Oguro, 1961, Fig. 3D in S. lindbergi).

The two-pointed sigmoid of S. stepanovi may have been originated by deviating from the usual course of development of sigmoid in the middle stages (cf. two-pointed sigmoids of S. stepanovi (Fig. 2A–I) and developmental stages of sigmoids in Taeniogyrus dunedinensis (Fig., 3G). The reduced calcareous ring without radial nerve notch, the medioventral position of the Polian vessel, and, perhaps, intestine without loop are probably paedomorphic characters (Smirnov, 2015).

Scoliorhapis dianthus 1 recently described from the area of Sado, Japan is very close to S. lindbergi on a number of characters: external appearance, color and body wall structure with crowded small warts when compressed (cf. Solis-Marin et al., 2014, Fig. 1A in S. dianthus and Fig. 1H in S. lindbergi); the structure of tentacles (cf. Solis-Marin et al., 2014, Fig. 1B, C in S. dianthus and Fig. 3E in S. lindbergi) and number of digits on tentacles (6 pairs of appendages in S. dianthus and 3-6 pairs in S. lindbergi); sigmoids size is 75 ± 5 Μ m on average in S. dianthus (Solis-Marin et al, 2014) and 70–100 Μ m (80 Μ m on average) in S. lindbergi (Oguro, 1961; Levin, 1982; Inoue & Kajihara, 2012). Thus S. dianthus is very close to S. lindbergi, and may be synonymous. We note that both species inhabit the Manchurian subregion of the Pacific Boreal (Steller) region (Kusakin 1979, 1990)— S. dianthus at its southern borders, and S. lindbergi at the northern.

Etymology. Named for Dr. Vadim Stepanov, Kamchatka branch of the Pacific Geographical Institute, Far- Eastern Branch of the Russian Academy of Sciences, with appreciation for his contribution to systematic and faunistic studies of the sea cucumbers of the Far Eastern Seas.