Dendronotus arcticus, Korshunova, Tatiana, Sanamyan, Nadezhda, Zimina, Olga, Fletcher, Karin & Martynov, Alexander, 2016

Korshunova, Tatiana, Sanamyan, Nadezhda, Zimina, Olga, Fletcher, Karin & Martynov, Alexander, 2016, Two new species and a remarkable record of the genus Dendronotus from the North Pacific and Arctic oceans (Nudibranchia), ZooKeys 630, pp. 19-42 : 23

Taxon classification Animalia Nudibranchia Dendronotidae

Dendronotus arcticus sp. n. Figs 1, 3A

Type material.

Holotype, ZMMU Op-561, 19 mm long (preserved), Laptev Sea, R/V "Dalnie Zelentsy", sta. O-48, 74°34.9' N– 74°35.1'N, 115°43.4' E– 115°42.2'E, 04.10.2014, depth 15 m, drague, sand, collector O.L. Zimina. 3 paratypes, ZMMU Op-562-Op-564, same locality and collectors as holotype.

Type locality.

Laptev Sea.

Etymology.

After the Arctic region.

Diagnosis.

5-6 pairs dorsolateral appendages, colour brownish with scattered distinct opaque white dots, central tooth with up to 14 small denticles and reduced furrows, vas deferens moderate in length, penis long, bent.

Description.

Body elongate, up to 19 mm in length (Fig. 1 A–C), 6-8 branched appendages of oral veil, 5-6 appendages of rhinophoral stalks, 15-18 rhinophoral lamellae, branched rhinophoral lateral papilla present, 5-6 pairs dorsolateral appendages, 15-25 lip papillae. Dorsolateral appendages with moderate primary stalk, moderately branched secondary branches, and elongated tertiary branches (Fig. 1 A–C). Reproductive and anal openings placed laterally on right side. General colour brownish with scattered distinct opaque white dots on notum, tips of lateral appendages, oral appendages, lip papillae, and rhinophores (Fig. 1 A–C).

Dorsal processes of jaws inclined posteriorly at approximately 55° to longitudinal axis of jaw body and 0.47 of its length (Fig. 1D, E). Masticatory processes apparently bear indistinct denticles. Radula formula is 38 × 3 –9.1.9– 3. Central tooth weakly denticulated and bearing up to 14 small denticles (Fig. 1 G, H) with reduced furrows. Lateral teeth are short, slightly curved, bearing up to nine long denticles (Fig. 1I).

Reproductive system triaulic (Fig. 3A), ampulla twice folded, prostate consisting of 25-30 alveolar glands, vas deferens moderate in length expanding to voluminous penial sheath, vagina long and twisted, penis long and twisted (Fig. 1F), and bursa copulatrix is large, rounded, and elongated with small seminal receptaculum placed distally (Fig. 3A) (nomenclature of the seminal reservoirs according to Stout et al. 2011).

Biology.

Inhabits soft substrates (sand, mud) with gravel and small stones.

Distribution.

Central and eastern coastal waters of Arctic Ocean.

Remarks.

Dendronotus arcticus sp. n. is well separated from other species of the genus Dendronotus : externally Dendronotus arcticus sp. n. is readily distinguished from all species of the genus Dendronotus by a light brownish ground colour with few distinct scattered white dots. There is little variation of colour in Dendronotus arcticus sp. n. compared to that of other Dendronotus species. The radula of Dendronotus arcticus sp. n. is similar to those of Dendronotus albus and Dendronotus robilliardi sp. n. but clearly differs by its pattern of central and lateral teeth. The radular differences include the presence of reduced furrows on the central teeth of Dendronotus arcticus sp. n.: Dendronotus albus and Dendronotus robilliardi sp. n. have no furrows on their central teeth, whereas the central teeth of the common North Atlantic species Dendronotus frondosus have deep furrows. The common North Atlantic and Arctic species Dendronotus lacteus differs considerably from Dendronotus arcticus sp. n. by its radula (central teeth with deep furrows), colour, and reproductive system. Other species of the genus Dendronotus clearly differ from Dendronotus arcticus sp. n. by radular patterns. The reproductive system of Dendronotus arcticus sp. n. differs from those of Dendronotus albus and Dendronotus robilliardi sp. n. by the presence of a twisted penis, by the colour pattern of the dorsal appendages, by the shape of the central tooth, and by the thicker vagina. Dendronotus arcticus sp. n. can be clearly distinguished from the recently described NW Pacific species Dendronotus kamchaticus , Dendronotus kalikal , and Dendronotus primorjensis by the colour and the radular and reproductive system patterns.

Uncorrected p-distances are different between Dendronotus arcticus sp. n. and the sympatric Arctic species Dendronotus lacteus (range 10.0-10.8 % for COI, and 1.6-1.8% for 16S data set), and Dendronotus robustus (range 12.8-13.9% for COI, and 3.2-3.4% for 16S). P-distances are different between Dendronotus arcticus sp. n. and the North Pacific Dendronotus kamchaticus (range 8.6-10.0% for COI, and 2.3-2.7% for 16S), Dendronotus kalikal (10.1 % for COI, and 2.3-2.5% for 16S), and Dendronotus primorjensis (range 12.0-12.5% for COI, and 2.5-2.7% for 16S). Minimum interspecific distances of the COI marker separate Dendronotus arcticus sp. n. from other species with high genetic divergence: 10.1% from Dendronotus kalikal , 9.3% from Dendronotus kamchaticus , 10.5% from Dendronotus lacteus , 12.3% from Dendronotus primorjensis , and 13.4% from Dendronotus robustus .