Branchipolynoe onnuriensis, Kim & Choi & Eyun & Kim & Yu, 2022

Kim, Sang Lyeol, Choi, Hyeongwoo, Eyun, Seong-il, Kim, Dongsung & Yu, Ok Hwan, 2022, A New Branchipolynoe (Aphroditiformia: Polynoidae) Scale Worm from the Onnuri Deep-sea Hydrothermal Vent Field, Northern Central Indian Ridge, Zoological Studies 61 (21), pp. 1-14 : 4-6

publication ID	https://doi.org/ 10.6620/ZS.2022.61-21
DOI	https://doi.org/10.5281/zenodo.8075107
persistent identifier	https://treatment.plazi.org/id/BB199D03-6177-FF9B-18A0-FD82FDFDFE17
treatment provided by	Valdenar
scientific name	Branchipolynoe onnuriensis
status	sp. nov.

Treatment

Branchipolynoe onnuriensis sp. nov.

( Figs. 1–4 View Fig View Fig View Fig View Fig ) urn:lsid:zoobank.org:act:7E5DB4C2-75E2-4AD2-9BE7-A4860812BBC9

Material examined: Six specimens. Holotype (B_S_ MA_0031740) and five paratypes (B_S_MS_00031741- 5), collected from the OVF on the northern Central Indian Ridge (st. GTV 1906 - 11°24.96'S, 66°25.397'E, 2064 m depth). GoogleMaps

Etymology: Named in honor of the discoverer of the OVF.

Ecology: The new species is only known to occur in association with the hydrothermal vent mussel Gigantidas vrijenhoeki Jang et al. 2020 . It lives inside the pallial cavity of the host ( Fig. S1 View Fig ). The deep-sea OVF in the Indian Ocean is a hydrothermal system characterized by low-temperature diffuse emissions with high concentrations of dissolved methane ( Jang et al. 2020).

Description: Body slightly tapered anteriorly and posteriorly, flattened ventrally and arched dorsally, with 21 segments, first segment achaetous ( Fig. 1A, B View Fig ). Ten pairs of elytrophores and elytra on segments 2, 4, 5, 7, 9, 11, 13, 15, 17, and 19; elytra moderately large, smooth, oval without border papillae ( Fig. 2C– F View Fig ), covering the dorsum in the anterior and posterior regions, but leaving the mid-dorsum partially uncovered ( Fig. 1A, B View Fig ). Cirrophorous segments with short cylindrical cirrophores and short, smooth dorsal cirri with short slender tips, tapering gradually, exceeding the anterior and ventral cirri, not extending past the tips of neurochaetae ( Fig. 1A View Fig ).

Prostomium ellipsoidal, bilobed, with rounded anterior lobes. A pair of short conical palps and short conical median antennae between the two anterior lobes ( Fig. 1C View Fig ). Median antenna and palps smooth, tapering to slender tip; palps extending beyond prostomium. Prostomium lacking frontal peaks, eyes, and lateral antennae. First segment with two pairs of tentacular cirri, fused to the prostomium; tentacular cirri smooth, slightly slender, not exceeding prostomium length ( Fig. 1C View Fig ). Thick, muscular pharynx with five pairs of dorsal and ventral small, sac-like terminal papillae surrounding the mouth ( Fig. 2A View Fig ).

Branchiae on segments 3–21, dense, arborescent, with short terminal filaments ( Fig. 2B View Fig ), not extending beyond the elytral border, gradually decreasing in size anteriorly and posteriorly, separated into two types emerging dorsally and ventrally, respectively. Dorsal tubercles non-discernible.

Parapodia subbiramous. Notopodia smaller than neuropodia, with few notochaetae projecting beyond notopodia ( Fig. S2 View Fig ). Neuropodia large, rounded, enclosing numerous neurochaetae with rounded lobes. Notochaetae smooth; stouter and shorter than neurochaetae ( Fig. 3A View Fig ). Notochaetae few (up to 8 per parapodium), more numerous in middle and posterior than anterior segments, slightly tapering, with serrated distal parts, rounded unidentate tips and shafts with indistinctive serrations ( Fig. 3B–D View Fig ). Neurochaetae numerous, more abundant on middle than anterior and posterior segments, arranged as a lateral fan, tapering, with subdistal swelling and small spines along the edge, serrations starting at the midpoint of the expanded distal part on only one side and extending distally; supraacicular neurochaetae long, stout, with slender tips, bidentate, with hooked distal teeth, serrated distally and flattened on one side; subacicular neurochaetae similar to supraacicular but with shorter distal serrated parts ( Fig. 4 View Fig ).

Ventral cirri smooth, small, lacking papillae, inserted in the middle of neuropodia; projecting anteriorly ( Fig. 1D View Fig ). Nephridial papillae ventral, on segments 11 and 12 in females, long, reaching the next segment, projecting posteriorly ( Fig. 1D View Fig ). Pygidium small, round with a pair of short, stout, tapered anal cirri, not fused ( Fig. 1B View Fig ).

Morphological variation: Holotype 28 mm long and 13 mm wide (including parapodia); paratypes 23– 31 mm long and 8–14 mm wide (including parapodia). All specimens showing nephridial papillae on segments 11 and 12, suggesting all were females.

Remarks: Nine species of Branchipolynoe have been described ( Pettibone 1984 1986; Miura and Hashimoto 1991; Zhou et al. 2017; Lindgren et al. 2019; Wu et al. 2019). The diagnostic characteristics of this genus were established based on Branchipolynoe symmytilida and amended based on B. seepensis to include the first position of branchiae, the presence of cephalic peaks, and the form of parapodia ( Pettibone 1984 1986). Subsequently, B. longqiensis was described from the Indian Ocean and five additional species were described from the Pacific Ocean ( Lindgren et al. 2019; Zhou et al. 2017) ( Table S2 View Table 2 ). Members of this genus have 21 segments, 10 elytra partially covering the dorsal region and bilobed prostomium (except B. kajsae ) lacking cephalic peaks (except B. symmytilida ). Branchipolynoe onnuriensis sp. nov. most closely resembles B. longqiensis and B. tjiasmantoi in having branchiae starting on the third segment and subbiramous parapodia, but differs in the two latter species have short, rounded notopodial acicular lobes, inconspicuous pharyngeal papillae, and different tip shapes of their sub-acicular neurochaetae ( Table S3).