Adalaria ultima Martynov & Korshunova 2017, sp. nov.

Adalaria ultima sp. nov.

(Figures 1, 3; 5B)

http://zoobank.org/urn:lsid:zoobank.org:act:0684148E-3C12-4BEE-9C6D-CB33842EC258

Type Material. Holotype, ZMMU Op-551 (21 mm length), NW Pacific Ocean, Okhotsk Sea, Sakhalinsky Bay, depth 95 m, collector not known, 1985. Paratypes, 2 specimens, ZMMU Op-552, NW Pacific Ocean, Japan Sea, off Moneron Island, depth 40–60 m, collector not known, 29.08.1978.

Type locality. Okhotsk Sea, Sakhalinsky Bay.

Etymology. This species is named in reference to the remote far eastern range of this species in the north-west Pacific compared to the high latitude Arctic habitat of the related species A. rossica. Ultimus in Latin means far, and is an adjective.

Description. External morphology. The length of the preserved holotype is 21 mm and 7 mm wide (Fig. 3 A– B). The lengths of two preserved paratypes are 12 mm and 19.5 mm, their widths 4 mm and 7 mm. The notum is moderately broad, rounded in front and posteriorly. The rhinophores are long and retracted into sheaths with smooth edges, except for several tubercles of various size that are connected to the edge of each sheath. There are 12–19 rhinophoral lamellae. The notum is densely covered with slender, narrow, elongated tubercles. Tubercules are alike all over the notum, narrow and elongated (Fig. 3 A). Larger tubercles are regularly intermingled with smaller ones. The rays of spicules radiating from the bases of tubercles form a sort of network under the surface of the soft notum. The spicules are not conspicuous externally. The gill cavity is absent. Eleven to twelve uni- and bipinnate gills form an almost complete semicircle around the anus, and one tubercle may be present just behind the anus. The large oral veil consists of two pairs of processes: a single, broad trapezoid upper triangular projection that is not medially fused with the hyponotum, and two flattened lobes below (Fig. 3 B). The foot is broad, anteriorly rounded, with no labium.

Colour. The living specimens are light yellowish white. The gills and rhinophores are more yellowish. There are no conspicuous white spots on the body and tubercles.

Anatomy. Digestive system. The anterior part of the buccal bulb is modified into oval buccal pump without distinct stalk (Fig. 3 C, D). The buccal pump is fully banded by a relatively narrow peripheral muscle (Fig. 3 D). The lateral parts of the buccal pump are provided with thin muscular fibres. The salivary glands are rounded (Fig. 3 C). The rounded labial disk is covered by yellowish cuticle without evident labial elements. The radular formula of the holotype is 37 x 1 –10.1.1.1.10–1. The central tooth is small, rectangular, and folded (Figs 3 F, G). The first lateral tooth has a long, wide base and a strong nearly straight and smooth cusp (Fig. 3 G). The outer denticles gradually reduce in size towards the internal ones. Outer lateral teeth have slightly elongated bases, with a curved, hooked cusp on its lateral corner; all are similar in size and shape (Fig. 3 G). The stomach is relatively small and narrow (Fig. 3 E), a stomach caecum is absent.

Circulatory system. In the pericardial sac a triangular posterior auricle and a smaller sized oval ventricle are present (Fig. 3 E). The blood gland lies above central nervous system and encompasses both posterior and anterior lobes.

Central nervous system. The cerebral and pleural ganglia are clearly separated. The optic nerve is short. The eyes are small and black. The pedal ganglia are similar in size to the cerebrals. The rhinophoral ganglia are globular. The buccal ganglia are slightly oval. Gastroesophageal ganglia are not differentiated. Five to six pairs of cerebral nerves, three to four pleural nerves, and three pedal ones are detected.

Reproductive system. (Figs 3 E, 5B). The ampulla is short, thick, not coiled (Fig. 5 B, a). The post-ampullar duct bifurcates into a long vas deferens and a short proximal oviduct. The long convoluted thick prostate (Fig. 5 B, pr) transits to a long single-looped penial sheath, which contains several thick loops of the ejaculatory duct (Figs 3 E, 5B, psh). The penial sheath and the ejaculatory duct (penis) are long and thick, without spines (Figs 3 B; 5B, p). The large globular bursa copulatrix enters into the vagina via a short narrow stalk (Fig. 5 B, b). The seminal receptacle is hidden within female gland mass (Figs 3 E, 5B, fgm).

Biology. The specimens were found predominantly on a mixed stony and sandy ground, at 40–106 m depth.

Distribution. Okhotsk Sea, the northern parts of the Sea of Japan.

Remarks. A morphological review of all known species of the genus Adalaria has been published recently (Martynov et al. 2009). The only morphologically similar species to Adalaria ultima sp. nov. is A. rossica sp. nov. described above. However, A. ultima sp. nov. is distinguished from the Arctic species by elongate, and not rounded tubercles in the middle part of the notum, a short non-coiled ampulla, and a larger bursa copulatrix. Because all material of this species was preserved in formalin a molecular analysis could not be performed. When molecular data will be available for A. ultima sp. nov. its phylogenetic relationship to the other species can be revisited.