Branchinotogluma kaireiensis sp.nov.

(Fig. 4)

ZooBank registration: urn:lsid:zoobank.org:act: 3481E7B6- 372B-44B0-967A-5023DF37F339.

Branchinotogluma sp. CIR— Zhou et al. 2022.

Diagnosis: Large-sized (about 38 mm in maximum) Branchinotogluma with 10 pairs of elytra and arborescent branchiae on segments 3–21. Seven pairs of short, ventral papillae on segments 11–17 on female; four pairs of well-developed ventral papillae present on segments 12–15, and two pairs of ventral lamellae on segments 16 and 17 on male. Notopodia without bracts. Pharynx with three dorsal and two ventral papillae and a pair of rounded lateral papillae surrounding the opening.

Type locality: Kairei vent field, CIR.

Type material: Holotype (NSMT-Pol_P-921): female, 38.22 mm in length, 20.72 mm in width, Kairei vent field (25.32°S, 70.04°E, 2434 m deep), CIR, Dive 1450, 14 February 2016. Paratype 1 (NSMT-Pol_P-922): female, 8.63 mm in length, 4.02 mm in width, same collecting data as holotype. Paratype 2 (NSMTPol_P-923): male, 12.25 mm in length, 13.93 mm in width, same collecting data as holotype. Paratype 3, (RSIO72112): Wocan vent field (6.36°N, 60.53°E, 2970 m deep), Dive 211, 30 May 2022 .

Description: Body short, 21 segments, spindle-shaped, slightly tapered anteriorly and posteriorly, flattened ventrally, and arched dorsally (Fig. 4A, B). Elytra 10 pairs, on segments 2, 4, 5, 7, 9, 11, 13, 15, 17, and 19, large, imbricated, rounded, or subreniform, iridescent when fresh and pale white in ethanol (Fig. 4C); elytrophores long, cylindrical (Fig. 4D). Branchiae arborescent, with very short, terminal filaments (Fig. 4D), present on segments 3–21, larger on middle segments than on anterior and posterior ones; branchiae separated into two clusters, with one attached to the lateral side of dorsal tubercles or elytrophore (Fig. 4D, L) and the other at the bases of notopodia (Fig. 4D, M), which may be absent from the last two segments (Fig. 4H).

Prostomium deeply bilobed, anterior lobes subtriangular with frontal filaments (Fig. 4E). Middle antenna inserted in anterior notch, with cylindrical ceratophore extending to tips of anterior lobes of prostomium; style long, surpassing prostomium. Eyes absent (Fig. 4E). Pair of smooth, stout, long, and tapering palps attached to lateral sides of prostomium (Fig. 4E, F). First achaetous segment fused to prostomium, not distinct dorsally (Fig. 4F); two pairs of the tentacular cirri shorter and more slender than palps (Fig. 4F). Segment 2 without bract, bearing the first pair of elytra; ventral cirri longer than following ones (Fig. 4E, F). Mouth ventrally located between segments 1 and 2 (Fig. 4F). Pharynx, when everted, with a pair of rounded papillae at the lateral sides, three dorsal and two ventral papillae surrounding the opening; two pairs of jaws each with c. 30 teeth on the inner border (Fig. 4G).

Parapodia biramous, with notopodia usually shorter than neuropodia, except on segment 2 (Fig. 4K–N). Notopodia with elongate acicular lobes on lower side (Fig. 4H, I, K–M), lacking in bracts; neuropodia well developed, with elongate triangular prechaetal lobe and shorter, rounded postchaetal lobe (Fig. 4L, M). Dorsal cirri long, filamentous, with long, cylindrical cirrophores, attached basally to the dorsal side of notopodia on non-elytrigerous segments (Fig. 4N). Ventral cirri shorter than dorsal cirri, with tapered ends (Fig. 4I, M).

Notochaetae stout, straight, in radiating bundles (Fig. 4L, M), with two rows of minute spines in distal two-thirds part (Fig. 4O). Neurochaetae in fan-shaped bundles, numerous, slender (Fig. 4L, M). Supraacicular neurochaetae straight with hooked tips and two rows of prominent spines (Fig. 4P). Subacicular neurochaetae long, more numerous than supraacicular neurochaetae, with two rows of feather-like serrations (Fig. 4Q).

Ventral papillae seven pairs, short, present on segments 11–17 (Fig. 4B). Pygidium with a pair of long and slender anal cirri (Fig. 4I).

On male, branchiae present on segments 3–16. Ventral papillae four pairs, present on segments 12–15, well-developed, with tapered ends (Fig. 4J); ventral lamellae two pairs, present on segments 16 and 17. Segment 19 modified with much smaller elytrophores and smaller elytra; notochaetae similar to that on previous ones; neurochaetae numerous with two rows of widely-spaced, long spines beginning subdistally and extending to tips. Segments 20 and 21 fused ventrally, strongly modified (Fig. 4I); notopodial acicular lobes fused to long cirrophores of dorsal cirri, with a few notochaetae (Fig. 4N); neuropodia with elongated post-acicular lobes, ventral cirri long, extending to the end of neuropodia (Fig. 4N); neurochaetae long and slender, with two rows of prominent spines beginning subdistally on both sides and extending to tips (Fig. 4R).

Etymology: The species is named after the type locality, Kairei vent field, CIR.

Distribution: The species is currently known from Kairei vent field, CIR and Wocan vent field, CR.

Remarks: Branchinotogluma kaireiensis sp. nov. can be distinguished from most congeners by having seven pairs of short, rounded, ventral papillae on females. On this basis, Branchinotogluma kaireiensis sp. nov. is most similar to B. burkensis Pettiboneae, 1989 and B. pettiboneae Wu et al., 2019, both with seven pairs short ventral papillae on females. The new species can be distinguished from B. burkensis and B. pettiboneae by lacking notopodial bracts in all segments.