Branchinotogluma sagamiensis sp. nov. [Japanese name: Sagami-tsunodashi-urokomushi] Zoobank LSID: urn:lsid:zoobank.org:act: 174E1034-D587-467D-BADA-E80B0D279451 Type locality: Hydrocarbon seep area, Off Hatsushima, Sagami Bay (36°00.957' N, 139°13.325' E), Japan, 867 m in depth. Material examined: Holotype (NSMT-Pol H-885): male, Sagami Bay, 867 m depth, ROV KM-ROV, R / V Kaimei, February, 2021, collected by CC. Paratype (NSMT-Pol P-886): one specimen, female, collected with the holotype. Description: Male 8 mm long, 3 mm wide (with parapodia, without chaetae), with 20 segments, flat (Fig. 4). Living colour purple-red. Body without dorsal tubercles. Ten pairs of elytra on segments 2, 4, 5, 7, and alternating segments to 19. Elytra transparent, without fringing papillae at outer margins, without microtubercles and macrotubercles. Bilobed prostomium pinkish in live specimens (whitish in ethanol) bilobed, with distinct anterior lobes; anterior lobes cylindrical, without conical frontal filaments (Figs 4C, 6A). Median antenna with short cylindrical ceratophore, inserted at anterior notch of prostomium (Figs 4C, 6A); style 0.5 mm, not papillate, thin and tapered. Lateral antennae absent. Eyes absent. Palps as long as ventral tentacular cirri (Figs 4C, 6A), whitish, smooth, tapered in tips. Dorsal and ventral tentacular cirri with tentaculophores lateral to prostomium. Dorsal tentacular cirri longer than ventral tentacular cirri. Dorsal and ventral tentacular cirri whitish, not papillated. One pair of short, thick ventral papillae present on segment 12 (Figs 4D, 6B). Ventral segmental lamellae near ventral bases of neuropodia present on segments 13–18 (Figs 4D, 6B). Pygidium with a pair of pygidial cirri, long and slender (Figs 4D, 6B). Parapodia biramous (Figs 5B, 6C). Notopodia shorter than neuropodia. Notopodia with short conical acicular lobes, on elytrigerous segments, with prominent bracts enclosing notochaetae dorsally and posteriorly (Figs 5B, 6C). About 50 notochaetae in each notopodium. Notochaetae short to long, with distinct rows of spines along one side, tapering to blunt tips, unidentate (Figs 5C, 6D), stouter than neurochaetae. Neuropodia with subconical prechaetal lobes tapering to sharp tips; post chaetal lobes shorter, rounded. Neurochaetae of one type, numerous, short to long, with borders finely spinous, tips slightly hooked and finely spinous, spines long and widely spaced in subdistal region, without semi-lunar pockets (Fig. 5D). Robust acicula in each ramum. Ventral cirri tapered, not papillated, attached on middle part of parapodia. On segment 2, ventral cirri elongated and projecting from neuropodia. Branchiae present from chaetigers 3 to 16, short, with 8–10 filaments, arborescent, two pouches per parapodium. Pharynx with four pairs of papillae terminally and two pairs of jaws.Jaws growing inwardly, with minute denticles. Variation: Paratypes 7 mm long, 2 mm wide. Ventral papillae absent in female specimen. Etymology: Named after the type locality (Sagami Bay). The specific name is an adjective. Distribution: Hydrocarbon seep area, 867 m, Off Hatsushima, Sagami Bay, Japan, Northwest Pacific Ocean. Remarks: This new species resembles Branchinotogluma trifurcus (Miura & Desbruyères, 1995) in having a cylindrical anterior lobe, absence of conical frontal filaments, and presence of short ventral papillae (Miura & Desbruyères 1995). The new species can be differentiated from B. trifurcus by the following features: i) 20 segments; ii) dorsal tentacular cirri longer than ventral tentacular cirri; iii) ventral segmental lamellae near ventral bases of neuropodia present on segments 13–18; iv) median antenna thin. This is the first record of Branchinotogluma from a hydrocarbon seep in Japan. Although categorized as a seep due to the typically cool temperature, the geofluid of the Off Hatsushima seep is probably hydrothermal in origin, since fluids as high as 11.6°C have been measured and the temperature of the end-member is said to be 34–54 °C (Tsunogai et al. 1996).

Published as part of Jimi, Naoto, Chen, Chong & Fujiwara, Yoshihiro, 2022, Two new species of Branchinotogluma (Polynoidae: Annelida) from chemosynthesis-based ecosystems in Japan, pp. 17-30 in Zootaxa 5138 (1) on pages 23-26, DOI: 10.11646/zootaxa.5138.1.2, http://zenodo.org/record/6552075