Adalaria rossica Martynov & Korshunova 2017, sp. nov.

Adalaria rossica sp. nov.

(Figures 1, 2; 5A)

http://zoobank.org/urn:lsid:zoobank.org:act:192632D5-29F7-4857-BB60-6B4101509884

Type Material. Holotype, ZMMU Op-548, (19.5 mm length, 11 mm width fixed), Arctic Ocean, Franz Josef Land, Kuhn Island, 18–31 m, leg. O.V. Savinkin, 16.08.2013. Paratypes, ZMMU Op-549, 1 specimen (16 mm length, 13.5 mm width, fixed), Arctic Ocean, Franz Josef Land, Heiss Island, 9–25 m, stones, sand, sta. G13, leg. O.V. Savinkin, 12.08.2013. ZMMU Op-550, 1 specimen (12 mm length, 12.5 mm width, fixed), Arctic Ocean, Franz Josef Land, Nansen Island, 6–21 m, stones, sand, sta. G31, leg. O.V. Savinkin, 23.08.2013.

Type locality. Arctic Ocean, Franz Josef Land.

Etymology. This species is named in honour of Russian underwater explorers who previously investigated marine opisthobranch fauna of the extremely cold water of Franz Josef Land and adjacent Arctic regions, including A.N. Golikov, M.V. Propp, A.F. Pushkin, B.I. Sirenko, and others, and those who collected this species in 2013, O.V. Savinkin and S.D. Grebelnyi. They have made great contributions towards the understanding of the fauna and flora of one of the most northern territories of the world.

Description. External morphology. The length of the preserved holotype is 19.5 mm and width 11 mm (Fig. 2 A). The length of three preserved specimens ranged from 14 to 19.5 mm, the width ranged from 9 to 15 mm. The notum is moderately broad, rounded in front and posteriorly. The rhinophores are long and retracted into sheaths with smooth edges, except for 5–7 tubercles of various size that are connected to the edge of each sheath. There are 38–42 rhinophoral lamellae. The notum is densely covered with narrow, elongate spine-like tubercles. Tubercles in the central notal area are somewhat wider and more globular than those at the notal edge (Fig. 2 A, B). 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 apparently soft notum. The spicules are not conspicuous externally. The gill cavity is absent. Ten to twelve uni- and bipinnate gills form an almost complete semicircle around 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. 2 A). The foot is broad, anteriorly rounded, without 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 or on the tubercles.

Anatomy. Digestive system. The anterior part of the buccal bulb is modified into the prominent, massive oval buccal pump on a short distinct stalk (Fig. 2 C, D). The buccal pump is fully banded by a relatively narrow peripheral muscle (Fig. 2 D). The lateral parts of the buccal pump are equipped with thin muscular fibres. The salivary glands are rounded (Fig. 2 C). The rounded labial disk is covered by yellowish cuticle without evident labial elements (Fig. 2 F). The radular formula in the 16 mm length specimen is 46 x 1 –10.1.1.1.10–1. The central tooth is small, elongated, rectangular, and folded (Fig. 2 G, H). The first lateral tooth is provided with a long, wide base and a strong, almost straight, smooth cusp (Fig. 2 H). 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. 2 G, H). In the middle and posterior part of radula up to 10 lateral teeth, whereas at anterior part their number may be reduced to a single tooth. The stomach is relatively small and narrow (Fig. 2 E), the stomach caecum is absent.

Circulatory system. In the pericardial sac a triangular posterior auricle and a smaller sized oval ventricle are present (Fig. 2 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 well separated. The optic nerve is short. The eyes are not large, with black pigment. 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. Four pairs of cerebral nerves, three to four pleural and three pedal ones are detected.

Reproductive system. (Figs 2 E, 5A). The ampulla is long, thick and characteristically coiled (Figs 2 E, 5A, a). The post-ampullar duct bifurcates into a long vas deferens and a short proximal oviduct. The long convoluted thick prostate (Fig. 5 A, pr) transits to a long single-looped penial sheath, which contains several thick loops of the ejaculatory duct (Figs 2 E, 5A, psh). The penial sheath is long and thick, the ejaculatory duct (penis) without spines (Fig. 5 A, p). The small globular bursa copulatrix is connected into the vagina via a short narrow stalk (Fig. 5 A, b). The seminal receptacle is hidden within the female gland mass (Figs 2 E, 5A, fgm).

Habitat. Specimens were found predominantly on mixed stony and sandy ground, at 6–31 m depth.

Distribution. Franz Josef Land.

Remarks. The new species of Adalaria is distinguishable from all recently described species (Martynov et al. 2009; Martynov, Sanamyan, Korshunova 2015a) by the presence of elongated dorsal tubercles; by this character the new species also clearly differs from A. proxima (Alder & Hancock, 1854) and A. loveni (Alder & Hancock, 1862), which have a similar radula. Results obtained by PopART showed a network of haplotypes that clearly clustered into two groups coincident with A. rossica sp. nov. and A. proxima (Fig. 6 A). Genetic p-distances clearly separate A. rossica sp. nov. from the morphologically similar species A. proxima as well as from all other described species of the genus Adalaria. Uncorrected minimal COI p-distances are different between A. rossica sp. nov. and A. proxima (range 8.97±1.1%). Interspecific distances separate A. rossica sp. nov. from A.proxima with a genetic divergence of 9.1%, whereas intraspecific divergence is 0% in A. rossica sp. nov. and 1.1% in A. proxima. In addition, the only previously reported Arctic species, A. tschuktschica Krause, 1885, is considerably different from A. rossica sp. nov. in the shape of the first lateral teeth and the number of the outer lateral teeth (see Martynov et al. 2009 for details). Thus initial genetic data and analyses support the morphology-based conclusions that A. rossica sp. nov. is a new species.