Onchidoris macropompa Martynov, Korshunova, Sanamyan & Sanamyan, 2009, sp. nov.

Onchidoris macropompa sp. nov.

(Figures 6 I, J; 7D; 13; 14A–F; 15A, B. Table 3)

Onchidoris sp.: Martynov, 1997: 235

Material. Holotype, ZMMU Lc-37463, NW Pacific near Kamchatka peninsula, Starichkov Id., 6–7 m depth, collected by T.A. Korshunova and A.V. Martynov, 25.07.2008. Paratypes, Lc-37464, two specimens (one dissected), same locality and collectors as holotype, 25.07.2008. Paratype, ZMMU Lc-37465, one specimen (dissected), 21–26 m depth, same locality and collectors as holotype, 14.08.2008. Paratypes, ZMMU Lc- 37466, two specimens (dissected), 12–15 m depth, same locality and collectors as holotype, 19.08.2008; Paratype, ZMMU Lc-37467, one specimen (dissected), Commander Ids., Medny Id., Cape Drovyanye Stolby, sample 101, 9– 12 m depth, collector Oshurkov V.V., 17.07.1992. Paratype, ZMMU Lc-37468, one specimen (dissected), Commander Islands, Beringa Id., Ariy Kamen Id., sample 225, 25 m depth, rock, collector V.I. Shalukhanov, 0 2.08.1991. Paratypes, Lc-37469, two specimens (one dissected), Commander Islands, Mednyi Id., Kekur Korabelny Stolb Id., 18–19 m depth, rock, collector V.I. Shalukhanov, 11.07.1992.

Type locality. NW Pacific, SE Kamchatka, Starichkov Id., 6–26 m depth.

Etymology. From macros (Greek, = large) and pompa (Russian, Italian, = pump) refers to the largest relative size of the buccal pump of the present species within Onchidorididae.

Description. External morphology. The length of holotype is 7 mm, the width is 4 mm (Fig.13 A). The length of 5 living specimens ranged from 6 to 15 mm, the width ranged from 4 to 6.5 mm. The consistency of the living animals is hard. The notum is moderately broad, rounded in front and posteriorly. The rhinophores are long and retract into sheaths with smooth edges, except for 3–4 tubercles of various sizes that are connected with the edges of the sheaths (Fig. 13 F). The rhinophoral sheath edges are capable of some contraction in living specimens. There are 7–13 rhinophoral lamellae. The notum is densely covered with mushroom-shaped or club-shaped tubercles on a short stalk. The larger tubercles dominate all over the notum, but a single irregular zigzag row of smaller tubercles appears in the mid-notal line. Some smaller tubercles are also scattered around various notal areas and at the edge of the notum. The rays of the spicules that extend from the bases of tubercles form a dense network that shines through the notum surface (Figs. 6 I; 13A, D). Each tubercle contains dense bundles of spicules, characteristically slightly protruding from the tubercle surface. The strongly calcified spicules are of various sizes; most have a narrow channel inside, some are solid (Fig. 6 J). A gill cavity is absent. Inside the gill circlet there are several narrow tubercles of variable height. Ten to twelve unipinnate gills form a semicircle around the anus (Fig. 13 D). The oral veil is semicircular (Figs. 13 B, C). The foot is broad, anteriorly rounded and thickened, and posteriorly not projecting beyond the notum, forming a rounded tail (Fig. 13 A).

Colour. The living specimens are off-white, semitransparent. Rhinophores (including lamellae) and gills are similar to the ground colour. Dull white gill glands are placed at the gills base. A postbranchial gland is indicated by a slightly conspicuous flattened area behind the gills.

Anatomy. Digestive system. The anterior part of the buccal bulb is modified to a prominent, large, very broad, buccal pump that sits on a short, narrow, conspicuous stalk (Fig. 7 D). The buccal pump is fully banded by the broad peripheral muscle (Fig. 7 D). Lateral sides of the buccal pump are provided with thin muscular fibres. The rounded labial disk is covered by colourless cuticle with indistinct labial elements. The radular formula in five specimens (8–15 mm length) is 35– 38 x 1.1.1.1.1, radular teeth are almost colourless. The central tooth is distinct, relatively large, elongated, rectangular, and folded (Figs. 14 A–C, E). The first lateral tooth is provided with a long, wide base and a strong, almost straight beak-shaped cusp. All teeth are entirely devoid of any denticles (Figs. 14 A–F). The second lateral teeth are rectangular plates, with a downward directed cusp on its lower outside corner (Figs. 14 B–C; E–F). The stomach is relatively small and narrow. The stomach caecum is absent.

Circulatory system. In the pericardial sac there is a rather wide triangular posterior auricle and a smaller sized and also triangular ventricle. The massive blood gland forms a single piece that is located above the central nervous system and projects slightly anteriorly and posteriorly.

Central nervous system. The cerebral and pleural ganglia are well separated, the latter being somewhat smaller in size. The optic nerve is very short. The eyes are relatively large, with black pigment in all studied specimens. The pedal ganglia are smaller than the cerebrals, lay below them and are connected to them by very short connectives. The rhinophoral ganglia are rather irregular, globular or elongate. The buccal ganglia are slightly oval. Gastro-esophageal ganglia are present. Five pairs of cerebral nerves, two pleural and three pedal ones are detected.

Reproductive system. (Figs. 15 A, B). The ampulla is wide and swollen, somewhat kidney-shaped, and filled with sperm (Figs. 15 A, a). A long post-ampullar duct is placed along a shallow groove in between the seminal receptacle and vagina and then bifurcates into a long vas deferens (Fig. 15 A, pr) and the proximal oviduct (Fig. 15 A, pov). The prostatic part of the vas deferens is a relatively long loop adjacent to, but not encircling the bursa copulatrix (Fig. 15 A, pr). The prostate is narrow, not granulated; it narrows and then rapidly widens into a long swollen penial sheath; this forms ca. 2.5 loops, and contains several folds of the ejaculatory duct. (Fig. 15 A, psh). The everted penial sheath and ejaculatory duct (penis) have two short terminal processes, and a third, very long one, that are united into a trifurcate penis (Fig. 15 B, tp). The globular bursa copulatrix (Fig. 15 A, bc) contains a dark brown substance; it enters the proximal part of the vagina via a narrow, relatively long stalk. At its base, a duct, which is similar in diameter to the vagina, exits the vagina and leads to the ovoid seminal receptacle (Fig. 15 A, rs). The vagina is wide and long (Fig. 15 A, v). The small distal oviduct (Fig. 15 A, dov) exits the vagina (Fig. 15 A, v) close to the vaginal opening.

Biology. Specimens were found predominantly under small stones covered with several species of encrusting bryozoa, at 6–15 m depth, rarely down to 18–25 m depth.

Distribution. Presently known only from the type locality in Kamchatka waters and from Commander Ids. (Martynov 1997, as Onchidoris sp.; present study).

Remarks. Onchidoris macropompa sp. nov. is externally most similar to Onchidoris muricata but can be readily distinguished from the latter by the smooth cusp of the first lateral teeth, completely devoid of any traces of denticles and in all studied specimens from different, distantly placed localities (i.e. from Kamchatka and from Commander Islands) (Figs. 14 A–F). In contrast, numerous specimens of Onchidoris muricata from both North Atlantic and North Pacific waters always have revealed the presence of various numbers of cusp denticles (Thompson & Brown 1984; Millen 1985; present study, Figs. 14 G–I). In addition, the cusps of the first lateral teeth of Onchidoris macropompa are straight (Figs. 14 B–D, F), whereas in Onchidoris muricata it is typically distinctly curved (Figs. 14 H, I). In addition, Onchidoris macropompa differs from most other species of the genus Onchidoris by presence of a central tooth in the radula (see Table 3 for comparison). The single other congener with radula formula of 1.1.1.1.1 and having smooth first lateral teeth, O. bilamellata, differs from Onchidoris macropompa by its colouration, the shape of the buccal pump, the shape of the first lateral teeth, and the pattern of the reproductive system.