Branchinotogluma Pettibone, 1985

Lee, Won-Kyung & Kim, Se-Joo, 2024, Distribution extension of a vent scale worm Branchinotogluma bipapillata (Polychaeta, Polynoidae) in the Indian Ocean, ZooKeys 1215, pp. 139-149 : 139-149

Genus Branchinotogluma Pettibone, 1985

Branchinotogluma bipapillata Zhou, Wang, Zhang & Wang, 2018: 528–533, figs 1–7; table 1.

Material examined.

Indian Ocean • 2 ♂; Cheoeum ; 12°37.1'S, 66°07.6'E; depth 3018 m; 28 Mar. 2023; W-K Lee leg.; hydrothermal vent; GenBank: PP 600168 – PP 600169; KRIBB 310101 to KRIBB 310102 • 2 ♂, 2 ♀, 1 undetermined; Onnuri; 11°24.9'S, 66°25.4'E; depth 2009 m; 1–2 Apr. 2023; W-K Lee leg.; hydrothermal vent; GenBank: PP 600170 – PP 600174; KRIBB 310103 to KRIBB 310107 • 1 ♀, 2 undetermined; Onnare; 9°47.4'S, 66°41.9'E; depth 2993 m; 3 Apr. 2023; W-K Lee leg.; hydrothermal vent; GenBank: PP 600175 – PP 600177; KRIBB 310108 to KRIBB 310110 • 1 ♂, 1 ♀; Onbada; 9°48.9'S, 66°40.6'E; depth 2563 m; 4 Apr. 2023; W-K Lee leg.; hydrothermal vent; GenBank: PP 600178 – PP 600179; KRIBB 310111 to KRIBB 310112 • 2 ♂, 2 ♀; Saero; 11°19.7'S, 66°26.9'E; depth 3256 m; 7 Apr. 2023; W-K Lee leg.; hydrothermal vent; GenBank: PP 600180 – PP 600183; KRIBB 310113 to KRIBB 310116 .

Description.

Specimens relatively well preserved, with 21 segments, 12.0–51.0 mm in length and 5.0– 16.6 mm in width. Body shape fusiform, tapered anteriorly and posteriorly (Fig. 2 A, B , Table 2 ). Pairs of elytra on elytrophores on segments 2, 4, 5, 7, 9, 11, 13, 15, 17, and 19; elytra oval to subreniform, white, slightly transparent, with a smooth surface (Fig. 2 C – E ). Dorsal cirri on segments 3, 6, 8, 10, 12, 14, 16, 18, 20, and 21, extending beyond the tips of neurochaetae. Branchiae arborescent; grouped in two, one at base of the notopodia and another at base of dorsal tubercles or elytrophores; starting from segment 3 and ending between segments 18 or 21 (Table 2 ).

Prostomium bilobed, triangular anterior lobes with slender frontal filaments (Fig. 2 F ). Median antennae on anterior notch, with a cylindrical ceratophore and subulate style; palps thick, smooth, and end in subulate tips; lateral antennae and eyes absent (Fig. 2 F ). Tentacular segment fused to prostomium, with pair of tentacular cirri on each side, and a small acicular lobe at the base of tentaculophore; tentacular cirri slender (Fig. 2 F ).

First segment not distinct, fused to prostomium. Pharynx with five dorsal and four ventral papillae in one immature individual, but not seen in others (Fig. 2 G ). Second segment with first pair of elytrophores, ventral cirri, and biramous parapodia. Third segment with ventral cirri and first pair of branchiae. Fourth to last segments with ventral cirri and biramous parapodia. Notopodia smaller than neuropodia; notochaetae stout, few, arranged in radiating bundles; neurochaetae slender, numerous, forming a fan shape (Fig. 2 H – K ).

Sexual dimorphism evident. In males, posterior segments modified (Fig. 3 A ) with 10 th elytra and elytrophores much smaller than 9 th (Figs 2 D , 3 A , Table 2 ); ventral papillae present on segments 12–13, long, tapering, with slender tips extending to next segment; ventral lamellae on segments 14–17, round (Fig. 3 B ). In females, posterior segments not modified (Fig. 3 C ), with 10 th elytra and elytrophores similar to 9 th (Figs 2 E , 3 C , Table 2 ); ventral papillae present on segments 11–15, short and blunt (Fig. 3 D ).

Distribution.

Indian Ocean (depth 1732–3256 m): Longqi and Duanqiao vent fields on the southern Southwest Indian Ridge; Tiancheng vent field on the northern Southwest Indian Ridge; Edmond vent field on the southern Central Indian Ridge; Onnare, Onbada, Saero, Onnuri, and Cheoeum vent fields on the northern Central Indian Ridge.

Remarks.

Comparisons of key morphological characters between the geographically distant populations are present in Table 2 . The key characters of the nCIR specimens of B. bipapillata largely correspond with those of the SWIR specimens ( Zhang et al. 2018). However, the two populations differ in the last segment with branchiae in females (segment 19 in sSWIR compared with segment 18 or 21 in nCIR; Table 2 ).

Among the 16 specimens from the nCIR population, 10 specimens with body length greater than 20 mm were well-developed in all features indicating adult morphology, while characters of sexual dimorphism were not observed in 6 specimens shorter than 20 mm.

DNA barcoding and phylogenetic analysis.

Partial sequences of CO 1, 16S, and 18 S were recovered from 16 specimens collected from the nCIR. As shown in Table 1 , 48 newly obtained sequences have been deposited in GenBank.

In CO 1, the mean intra-population variation was 0.56 % for nCIR and 0.65 % for SWIR, with an inter-population variation of 1.00 % (Table 3 ). In 16 S, the mean intra-population variation was 0.27 % for nCIR and 0.33 % for SWIR, with an inter-population variation of 0.39 %. In 18 S, the mean intra-population variation was 0.01 % for nCIR and 0.00 % for SWIR, with an inter-population variation of 0.004 %.

The interspecific variation between B. bipapillata and other congeners ranged from 18.63 % to 21.88 % in CO 1, and from 13.11 % to 19.08 % in 16 S (Suppl. material 1: table S 2). In 18 S, the interspecific variation ranged from 1.69 % to 3.80 %.

The maximum likelihood phylogenetic tree, constructed with concatenated sequences of CO 1, 16S, and 18 S (Fig. 4 ), shows the SWIR and nCIR populations of B. bipapillata clustering together as a single clade, indicating no significant divergence between populations from different ridges. Within the Branchinotogluma genus, B. bipapillata is closely related to a clade including B. kaireiensis , B. pettiboneae Wu et al., 2019 , and B. robusta Wu et al., 2023 .

Figures

Figure 2. Branchinotogluma bipapillata specimens collected from the nCIR A dorsal and ventral views of male (KRIBB 310116) B dorsal and ventral views of female (KRIBB 310105) C 1 st – 8 th left elytra D 9 th – 10 th left elytra of male (KRIBB 310103) E 9 th – 10 th left elytra of female (KRIBB 310110) F head featuring prostomium, palps, tentacular cirri, and first parapodia on segment 2 (KRIBB 310112) G everted pharynx with dorsal and ventral papillae (KRIBB 310108). Anterior and posterior views of left parapodia on (H-I) segment 2 and (J-K) segment 11 (KRIBB 310106). Scale bars: 5 mm (A – E); 0.5 mm (F, G); 1 mm (H – K).

Figure 3. Sexually dimorphic characters of Branchinotogluma bipapillata A dorsal view of posterior segments B ventral view of segments 12–17 of male (KRIBB 310116) C dorsal view of posterior segments D ventral view of segments 11–15 of female (KRIBB 310105). Arrows point to 9 th and 10 th elytrophores (EP) pointed with arrows. Ventral papillae are outlined in red and ventral lamellae in blue. Scale bars: 2 mm (A, C); 1 mm (B, D).

Figure 4. Maximum-likelihood phylogenetic tree of Branchinotogluma species based on concatenated sequences of the CO 1, 16 S, and 18 S genes. Branchinotogluma bipapillata species are highlighted with a gray box. Red and black squares represent nCIR and sSWIR populations, respectively. GenBank accession numbers of the CO 1, 16 S and 18 S genes of the outgroup are noted next to the species names. Maximum-likelihood bootstrap support values > 60 are displayed next to the nodes.