Branchipolynoe longqiensis, Zhou & Zhang & Lu & Wang, 2017

Zhou, Yadong, Zhang, Dongsheng, Lu, Bo & Wang, Chunsheng, 2017, Description of a new branchiate scale-worm (Polychaeta: Polynoidae) from the hydrothermal vent on Southwest Indian Ocean Ridge, Zootaxa 4282 (1), pp. 123-134 : 124-133

publication ID	https://doi.org/ 10.11646/zootaxa.4282.1.7
publication LSID	lsid:zoobank.org:pub:C0A7E657-B46F-491B-9A13-CF4332571B2A
DOI	https://doi.org/10.5281/zenodo.6045271
persistent identifier	https://treatment.plazi.org/id/D75787C0-C77E-050C-06AB-FD6DFB1890B4
treatment provided by	Plazi
scientific name	Branchipolynoe longqiensis
status	sp. nov.

Treatment

Branchipolynoe longqiensis View in CoL n. sp.

( Figs. 1–10 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 )

Materials and methods. All four specimens fixed and preserved in 95% ethanol and from host mussels Bathymodiolus marisindicus Hashimoto, 2001 . Holotype (RSIO35401), Southwest Indian Ocean Ridge, Longqi vent field, HOV Jiaolong Dive94, 49.6502°E, 37.7839°S, 2761 m, 11 January 2015: about 27.1 mm long, 4.5 mm wide (without parapodia).

3 paratypes from the same vent fields as RSIO35401: 2 specimens (RSIO35012 and RSIO35279), HOV Jiaolong Dive94, 49.6502°E, 37.7839°S, 2761 m, 11 January 2015: about 25.2 and 26.3 mm long, 3.4 and 3.7 mm wide (without parapodia) respectively; 1 specimen (RSIO35430), HOV Jiaolong Dive90, 49.6501°E, 37.7833°S, 2736 m, 3 January 2015: about 25.7 mm long, 4.1 mm wide (without parapodia).

Description. Body short, slightly tapered anteriorly and posteriorly, flattened ventrally and arched dorsally. 21 segments with 10 pairs of elytra and short elytrophores present on segments 2, 4, 5, 7, 9, 11, 13, 15, 17 and 19 ( Figs. 1 View FIGURE 1 A–B, 6A–B, 7A–B). The elytra are moderately large, oval, opaque and smooth ( Figs. 2 View FIGURE 2 C–F), covering the anterior and posterior dorsal ends completely, but leaving the middle of the body just partially covered ( Figs. 1 View FIGURE 1 A, 6A, 7A). Dorsal cirri with short cylindrical cirrophores present on non-elytra-bearing segments; short styles with slender tips, often extending to about tips of neurosetae ( Figs. 3 View FIGURE 3 F, 4C), but with a few exceptions ( Figs. 3 View FIGURE 3 C, 3H); Dorsal tubercles on cirrigerous segments indistinct.

Prostomium oval, bilobed, with rounded anterior lobes, lacking frontal filaments ( Fig. 1 View FIGURE 1 C). Median antenna short, conical, with slender tip, inserted in anterior notch, without distinct ceratophore, extending beyond the prostomium. Palps short, stout, smooth and tapering to slender tips and extending beyond the prostomium. First tentacular segment fused to prostomium, not distinct dorsally; tentaculophores lateral to prostomium, achaetous, short and bulbous, with 2 pairs of tentacular cirri slender and slightly shorter than palps ( Fig. 1 View FIGURE 1 C).

Thick muscular pharynx extended on two paratypes (RSIO35012 and RSIO35430, Figs. 7 View FIGURE 7 C, 8C), with five pairs of dorsal and ventral small, delicate, sac-like papillae present on the upper and lower lips of the mouth ( Figs. 7 View FIGURE 7 C, 8C–D) and two pairs of small, dark amber-colored jaws, lacking denticulate base ( Fig. 8 View FIGURE 8 D).

Branchiae present on segments 3–21, well developed, arborescent, with rather short terminal filaments ( Figs. 2 View FIGURE 2 A–B, 3C–H, 4E–F, 6C–D). Branchiae separated into 2 short trunks, an upper larger one attached to lateral bases of elytrophores or dorsal tubercles and a lower and smaller group dorsal-posterior to the notopodia, e.g., branchiae on segment 8 ( Fig. 3 View FIGURE 3 F) and segment 12 ( Figs. 2 View FIGURE 2 A–B, 3H). Branchiae typically larger in middle region (for the examined specimens on segments 7–10), smaller anteriorly and posteriorly ( Fig. 10 View FIGURE 10 ).

Parapodia on segment 2 biramous, bearing the first pair of elytra ( Fig. 3 View FIGURE 3 A–B). Notopodium short, digitiform, with 2 notosetae projecting beyond notopodium; neuropodia large, rounded, enclosing numerous neurosetae; buccal cirri attached basally on the neuropodia, lateral to the ventral mouth and longer than the following ventral cirri ( Figs. 3 View FIGURE 3 A–B, 4A). Following parapodia biramous, with a short and digitiform notopodia and a long and rounded neuropodia ( Figs. 3 View FIGURE 3 C–H, 4C, F, 6E).

Notosetae few (up to 8 per parapodium), usually fewer on the anterior and more on the middle and posterior segments ( Fig. 10 View FIGURE 10 ). Notosetae stout and short, projecting beyond notopodia, slightly tapered distally, with serrated distal margin ( Figs. 4 View FIGURE 4 A–D, F–G, 6E–F). Neurosetae numerous, more in the middle region and less anteriorly and posteriorly; all of them tapered, wider subdistally, with serrations starting at the widest point and extending distally; serrations present on only one side ( Figs. 4 View FIGURE 4 C, 5A–E, 6G–I). Neurosetae divided into 3 groups: supraacicular, upper subacicular and lower subacicular neurosetae. Supraacicular neurochaetae stout, tips with a minute hook (which sometimes is missing, giving to the chaetae a aspect of blunt tip); distal part flattened on one side; serrations reaching the tips ( Figs. 5 View FIGURE 5 A, C, 6G). Upper subacicular neurosetae few, much stouter than notosetae and other neurosetae, with hooked tips; serrations not reaching the tips ( Figs. 5 View FIGURE 5 D, 6H, 9A–D). Lower subacicular neurosetae numerous, slender, with serrated distal margins; tips hooked with lateral denticles ( Figs. 5 View FIGURE 5 B, E, 6I). Serrated parts of subacicular neurosetae shorter than supraacicular neurosetae ( Fig. 4 View FIGURE 4 C). Lower subacicular neurosetae first emerging frontally to those in the upper subacicular shaft, arranged in partly disordered rows, with dorsal rows stouter than ventral rows ( Figs. 9 View FIGURE 9 A–D); supraacicular neurosetae showing similar arrangement as lower subacicular group ( Figs. 9 View FIGURE 9 B, C) except for the anterior and posterior segments ( Figs. 9 View FIGURE 9 A, D); upper subacicular without distinct pattern, shaft much wider than that of other neurosetae ( Figs. 9 View FIGURE 9 A–D). Acicula usually stouter than neurosetae, positioned near the ventral end of the supraacicular neurosetae shaft ( Figs. 9 View FIGURE 9 A–D).

Two pairs of ventral papillae present on segments 11 and 12, long, extending to the posterior margin of the next segment ( Figs. 1 View FIGURE 1 B, D, 6B, 7B). Pygidium with a pair of anal cirri, short, stout, tapered, inflated basally but not fused ( Fig. 7 View FIGURE 7 D).

Coloration. Color of living animal pink to red, parapodia darker than trunk, color in alcohol pale white to light tan.

Etymology. Name after the type locality Longqi vent field.

Distribution. In association with Bathymodiolus mussels and known from the deep-sea hydrothermal vents on Southwest Indian Ocean Ridge.

Remarks. Three species have already been described in the genus Branchipolynoe ( Desbruyères et al. 2006; Miura & Hashimoto 1991; Pettibone 1984; Pettibone 1986). The diagnostic characters for the genus were derived from B. symmytilida ( Pettibone 1984) , then amended by Pettibone to include B. seepensis ( Pettibone 1986) . The major revision by Pettibone (1986) includes the starting position of the first pair of gills, presence/absence of minute frontal filament, form of parapodia, notopodia, and the number of notosetae. Most characters hold true for B. pettibonae and B. longqiensis , except for the relative width of upper neurosetae to the lower neurosetae, which is variable in the genus ( Table 1). In addition, all four species show similar pharynx characters with respect to the papillae around the opening and the jaws, which help to distinguish them from other branchiate scale-worms, like the genus Branchinotogluma ( Pettibone 1985) .

It is easy to distinguish the new species from the other three by their morphological characters ( Table 1). B. symmytilida is distinct from B. longqiensis n. sp. by its small elytra, minute frontal filaments on the anterior lobes of prostomium, and starting position of the first pair of branchiae (segment 2, Pettibone 1984).

Noto, notosetae; Sup, supraacicular neurosetae; Sub, subacicular neurosetae; Usub, upper subacicular neurosetae; Lsub, lower subacicular neurosetae; “~”, subequal in width or slightly wider.

For Branchipolynoe seepensis , subacicular neurosetae are not divided further into upper and lower subacicular neurosetae; in Branchipolynoe pettibonae , the three groups of neurosetae show the similar form as each other, so their characters are combined in Table 1.

The biramous parapodia and the short terminal filaments from the branchiae are similar in B. longqiensis n. sp. and B. seepensis , described from the Gulf of Mexico and Mid-Atlantic Ocean Ridge ( Pettibone 1986). However, the new species has fewer and shorter notosetae and less developed notopodia than B. seepensis . They also have different types of neurosetae. Neurosetae in B. seepensis are more slender than the notosetae, and separated into two groups; the upper group has blunt tips, while the lower, slender group have hooked tips with some longer denticles ( Pettibone 1986). The new species has three groups of neurosetae, all with wider subdistal parts, serrated distal margin and slightly hooked tips, and the upper subacicular neurosetae are stouter than notosetae.

The new species is also similar to B. pettibonae from the west Pacific in most morphological characters ( Miura & Hashimoto 1991). However, the branchiae of B. pettibonae are well developed with long terminal filaments, parapodia are subbiramous with very small notopodia, notosetae are indistinct and more slender than neurosetae, and the differences in the width of the setae are not obvious except for the smallest paratype ( Miura & Hashimoto 1991). In contrast to B. pettibonae , B. longqiensis n. sp. has branchiae with rather short terminal-filaments, biramous parapodia with distinct notosetae, which are stouter than supraacicular and lower subacicular neurosetae, and strong upper subacicular neurosetae much stouter than all other setae. The new species is also distinct from the other three of the genus by its short, stout, tapered, basally inflated and unfused anal cirri ( Table 1).