Dendronotus jamsteci, Martynov & Fujiwara & Tsuchida & Nakano & Sanamyan & Sanamyan & Fletcher & Korshunova, 2020

Martynov, Alexander, Fujiwara, Yoshihiro, Tsuchida, Shinji, Nakano, Rie, Sanamyan, Nadezhda, Sanamyan, Karen, Fletcher, Karin & Korshunova, Tatiana, 2020, Three new species of the genus Dendronotus from Japan and Russia (Mollusca, Nudibranchia), Zootaxa 4747 (3), pp. 495-513 : 500-503

Dendronotus jamsteci sp. nov.

( Figures 1–2 , 5A )

http://zoobank.org/ B8DAC5AC-56F4-4C92-90EC-D48C5173772A

Type material. Holotype, JAMSTEC No. 1160047475, 17.5 mm long preserved, dissected, Cruise KS-16-J03, on board ID HPD #1952, Japan, Northern Honshu , off Otsuchi, 39° 18.5378’ N 142° 17.82’ E, 08 March 2016, depth— 670 m, collector Shinji Tsuchida . One paratype, JAMSTEC No. 1160047461, Cruise KS-16-J03, on board ID HPD #1952-07, Dive No. HPD #1952, 21.5 mm long (preserved), Japan, Northern Honshu , off Otsuchi, 39° 18.4453’ N 142° 18.0498’ E, 08 March 2016, depth— 761 m, collector Shinji Tsuchida . Five paratypes, JAM- STEC No. 1160047464, Cruise KS-16-J03, on board ID HPD #1952-10, Dive No. HPD #1952, 2– 7 mm long (preserved), Japan, Northern Honshu , off Otsuchi, 39° 18.4453’ N 142° 18.0498’ E, 08 March 2016, depth— 761 m, collector Shinji Tsuchida. Ca . 60 paratypes, JAMSTEC No. 1160047463, Cruise KS-16-J03, on board ID HPD #1952-09, Dive No. HPD #1952, 1.5–15 mm long (preserved), Japan, Northern Honshu , off Otsuchi , 39°18.4453’ N 142°18.0498’ E, 08 March 2016, depth— 761 m, collector Shinji Tsuchida . Three paratypes, JAMSTEC No. 1160047392, Cruise KS-16-J03, on board ID HPD #1950-16, Dive No. HPD #1950, 11– 11.5 mm long (preserved), Japan, Northern Honshu , off Otsuchi , 39° 18.7059’ N 142° 18.0498’ E, 05 March 2016, depth— 684 m, collector Shinji Tsuchida . Nine paratypes, JAMSTEC No. 1160047475, Cruise KS-16-J03, on board ID HPD #1952, 2 – 21 mm long, Japan, Northern Honshu , off Otsuchi , 39° 18.5378’ N 142° 17.82’ E, 08 March 2016, depth— 670 m, collector Shinji Tsuchida . Three paratypes, JAMSTEC No. 1160047380, Cruise KS-16-J03, on board ID HPD #1950- 4, 7– 18 mm long (preserved), Japan, Northern Honshu, off Otsuchi, 39° 18.6579’ N 142° 18.0498’ E, 05 March 2016, depth— 704 m, collector Shinji Tsuchida.

Type locality. Japan, off the Pacific coast of Northern Honshu .

Etymology. In honour of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) which has made a considerable contribution to the understanding of deep-sea fauna in Japan and worldwide.

Diagnosis. Body elongate, 6–7 pairs dorsolateral appendages, colour whitish with brownish spots and streaks, central tooth with well-defined denticles and furrows, vas deferens moderate in length, penis conical, moderately narrow.

Description. Body elongate, up to 21.5 mm in length ( Fig. 2A, B ), 6–9 branched appendages of oral veil, 4–5 appendages of rhinophoral stalks, 12–15 rhinophoral lamellae, branched rhinophoral lateral papilla present, 6–7 pairs dorsolateral appendages, 20–25 lip papillae. Dorsolateral appendages with thickened primary stalk, moderately branched secondary branches, and blunted tertiary branches ( Fig. 2A, C ). Reproductive and anal openings placed laterally on right side. General colour whitish with scattered distinct opaque white dots on notum, tips of lateral appendages, oral appendages, lip papillae, and rhinophores ( Fig. 2C ).

The jaws are ovoid with strong dorsal processes, denticles present. Masticatory processes bear ca. 60 denticles (holotype, including simple triangular and broadly lamellated ones ( Fig. 2D, E ). Radula formula is 33 × 1–6.1.6–1 (paratype 7 mm), 34 × 3–8.1.8–3 (holotype), 38 × 3–8.1.8–3 (paratype 20 mm), 29 × 3–8.1.8–3 (paratype 21.5 mm). Central tooth strongly denticulated and bearing up to 17 distinct denticles ( Fig. 2F ) with well-defined furrows. Lateral teeth are short, slightly curved, bearing up to 9 long denticles ( Fig. 2G ).

Reproductive system triaulic ( Fig. 5A ), ampulla moderately thin, triple folded ( Fig 5A , am), prostate consisting of 50–60 alveolar glands ( Fig. 5A , pr), vas deferens moderate in length ( Fig. 5A , vd) expanding to a narrow penial sheath ( Fig. 5A , psh), penis short and conical ( Fig. 5A, p ), vagina long and twisted ( Fig. 5A , vg), bursa copulatrix is medium-sized, rounded ( Fig. 5A , bc) with small seminal receptaculum placed distally ( Fig. 5A , rs).

Biology. On hydroids within sand and muddy substrates.

Distribution. Presently known only off the Pacific coast of Northern Honshu ( Japan), at depths of 670– 761 m.

Remarks. Dendronotus jamsteci sp. nov. is superficially similar to D. frondosus and D. primorjensis , but different in the details of 1) colouration: compared to D. frondosus and D. primorjensis , D. jamsteci sp. nov. has a weakly coloured whitish ground colour with dispersed brownish spots), 2) radula: D. jamsteci sp. nov. has different number of rows (up to 8 in D. jamsteci sp. nov., up to 9 in D. primorjensis , up to 10 in D. frondosus ) and denticles on the central (up to 17 denticles in D. jamsteci sp. nov., up to 18 in D. primorjensis , up to 14 in D. frondosus ) and lateral tooth (up to 9 denticles in D. jamsteci sp. nov., up to 8 in D. primorjensis , up to 7 in D. frondosus ), and 3) reproductive system: D. jamsteci sp. nov. considerably differs in the number of alveolar glands (50–60 in D. jamsteci sp. nov., 12–19 in D. primorjensis , 16–30 in D. frondosus ) as well as details in the patterns of the bursa and copulative organ arrangements. Importantly, according to the molecular phylogenetic data ( Fig. 1 ), D. jamsteci sp. nov. doesn’t belong to the clade comprised of D. frondosus , D. primorjensis and D. venustus (this species readily differs externally from D. jamsteci sp. nov. by its bright yellow markings or large amounts of opaque white pigment) ( MacFarland 1966; Stout et al. 2010) but is sister to the clade that includes D. subramosus and D. albus . However, both the latter species are considerably different morphologically from D. jamsteci sp. nov.. Particularly, although D. subramosus externally shares a similar brownish colouration with D. jamsteci sp. nov. it lacks lateral rhinophoral papilla common in most species of the genus Dendronotus including D. jamsteci sp. nov. By this feature, it readily differ from D. jamsteci sp. nov., whereas D. albus considerably differs from D. jamsteci sp. nov. by its uniform whitish or lilac colour and patterns of the radula and reproductive system. Such a discrepancy of molecular and morphological evolution is very interesting. From the NW Pacific species D. kalikal , D. jamsteci sp. nov. differs by the absence of subparallel brownish dorsal stripes, details of the radula and very significantly by the molecular data ( Fig. 1 ). Two other NW Pacific species, D. kamchaticus and D. zakuro sp. nov., are substantially different from D. jamsteci sp. nov. by their colouration and the smooth central teeth of their radula at the adult stage and in addition, they belong to a different molecular clade ( Fig. 1 ). None of these species inhabit bathyal depths as D. jamsteci sp. nov. does, and their bathymetric distribution is restricted to shallow waters, not deeper than 60 m. Recently, a deep-sea species off the NE Pacific coast, D. claguei, was described ( Valdés et al. 2018). For that species, only H3 gene data was provided in the cited publication, so the absence of COI and 16S data prevented its use here for molecular analysis because the H3 gene is almost identical for closely related species of the genus Dendronotus . D. claguei fundamentally differs from D. jamsteci sp. nov. by its uniform translucent white colour, radular details, and in addition D. claguei inhabits upper abyssal depths (2369 m) and not upper bathyal depths (670–761 m) as D. jamsteci sp. nov. does. Maximum intraspecific and minimum interspecific genetic distances for the COI marker in the species of the genus Dendronotus including D. jamsteci sp. nov. are presented in Table 2 .

Figures

FIGURE 1. Phylogenetic relationships of the species of the genus Dendronotus based on COI + 16S + 28S concatenated dataset inferred by Bayesian inference (BI). Numbers above branches represent posterior probabilities from BI; numbers below branches indicate bootstrap values for Maximum Likelihood. Summary of species delimitation results are noted by numbered, clusters from the ABGD analyses for the COI dataset.

FIGURE 2. Dendronotus jamsteci sp. nov. Holotype, JAMSTEC No. 1160047475, 17.5 mm length (preserved), Northern Honshu, off Otsuchi, 670 m depth. A, B. Dorsal and ventral views respectively, preserved holotype. C. Live holotype. D. Jaws, SEM; E. Masticatory processes of jaws, SEM; F. Radula, posterior part; G. Lateral teeth, posterior part. H. Collecting of specimens in situ by remotely controlled manipulators. I. Overview of one of the bio-tracking base stations installed at the depth 761 m from which specimens were collected. Scale bars: D, 500 μm, E,G, 20 μm, F, 50 μm. Photos: Alexander Martynov (A,B, D–G), Yoshihiro Fujiwara (C, H, I).

FIGURE 5. Reproductive systems. A. Dendronotus jamsteci sp. nov. B. Dendronotus zakuro sp. nov. C. Dendronotus bathyvela sp. nov. Abbreviations: am, ampulla; bc, bursa copulatrix; fgm, female gland mass; fo, female opening; p, penis; pr, prostate; psh, penial sheath; rs, receptaculum seminis; ud, uterine duct; vd, vas deferens; vg, vaginal duct. Scale bars: 1mm.