Distribution extension of a vent scale worm Branchinotoglumabipapillata (Polychaeta, Polynoidae) in the Indian Ocean

Abstract

Branchinotogluma Pettibone, 1985 is the most species-rich genus within the subfamily Lepidonotopodinae Pettibone, 1983, comprising 18 valid species from chemosynthesis-based ecosystems in the Pacific and Indian Oceans. Here, we report a new distributional record of Branchinotoglumabipapillata Zhou, Wang, Zhang & Wang, 2018, at the hydrothermal vent sites on the northern Central Indian Ridge (nCIR). This record represents the northernmost occurrence of B.bipapillata in the Indian Ocean. We conducted a comparative study of the nCIR population and other documented populations using distributional information, morphological traits, and genetic markers (two mitochondrial [COI, 16S rRNA] and one nuclear [18S rRNA] genes). While most morphological characters of B.bipapillata were consistent with those found in the Southwest Indian Ridge (SWIR), variations were noted in the segment with the last branchiae. Molecular data revealed that all populations of B.bipapillata form a single clade, indicating a wide distribution from the SWIR to nCIR, covering ~4,000 km across various ridges in the Indian Ocean. This study presents extensive distribution of a vent species with well-connected populations throughout the Indian Ocean, distinguishing it from many other vent species affected by the dispersal barrier in the Indian Ocean.

Keywords: 16S rRNA; 18S rRNA; CO1; deep-sea; hydrothermal vent; northern Central Indian Ridge; polynoids.

Figure 1.

Map displaying the geographic distribution of Branchinotoglumabipapillata in the Indian Ocean. Red indicates sampling locations from this study and black indicates records of B.bipapillata from previous studies. Some closely situated sampling sites (< 10 km apart, such as Onbada and Onnare, Saero and Onnuri) are marked with a single square.

Figure 2.

Branchinotoglumabipapillata specimens collected from the nCIRA dorsal and ventral views of male (KRIBB310116) B dorsal and ventral views of female (KRIBB310105) C 1^st–8^th left elytra D 9^th–10^th left elytra of male (KRIBB310103) E 9^th–10^th left elytra of female (KRIBB310110) F head featuring prostomium, palps, tentacular cirri, and first parapodia on segment 2 (KRIBB310112) G everted pharynx with dorsal and ventral papillae (KRIBB310108). Anterior and posterior views of left parapodia on (H-I) segment 2 and (J-K) segment 11 (KRIBB310106). Scale bars: 5 mm (A–E); 0.5 mm (F, G); 1 mm (H–K).

Figure 3.

Sexually dimorphic characters of BranchinotoglumabipapillataA dorsal view of posterior segments B ventral view of segments 12–17 of male (KRIBB310116) C dorsal view of posterior segments D ventral view of segments 11–15 of female (KRIBB310105). 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 CO1, 16S, and 18S genes. Branchinotoglumabipapillata species are highlighted with a gray box. Red and black squares represent nCIR and sSWIR populations, respectively. GenBank accession numbers of the CO1, 16S and 18S genes of the outgroup are noted next to the species names. Maximum-likelihood bootstrap support values > 60 are displayed next to the nodes.