Out of the Pacific: A New Alvinellid Worm (Annelida: Terebellida) From the Northern Indian Ocean Hydrothermal Vents

Yuru Han,Chunsheng Wang,Yadong Zhou,Dongsheng Zhang

doi:10.3389/fmars.2021.669918

Abstract

Alvinellids have long been considered to be endemic to Pacific vents until recent discovery of their presence in the Indian Ocean. Here, a new alvinellid is characterized and formally named from recently discovered vents, Wocan, and Daxi, in the northern Indian Ocean. Both morphological and molecular evidences support its placement in the genusParalvinella, representing the first characterized alvinellid species out of the Pacific. The new species, formally described asParalvinella miran. sp. herein, is morphologically most similar toParalvinella hesslerifrom the northwest Pacific, but the two species differ in three aspects: (1), the first three chaetigers are not fused inP. miran. sp., whereas fused inP. hessleri; (2), paired buccal tentacles short and pointed inP. mirabut large and strongly pointed inP. hessleri; (3), numerous slender oral tentacles ungrouped inP. mirabut two groups inP. hessleri. Phylogenetic inference using the concatenated alignments of the cytochrome c oxidase I (COI), 16S rRNA and 18S rRNA genes strongly supports the clustering ofP. mirawith two West Pacific congeners,P. hessleriand an undescribed species (Paralvinellasp. ZMBN). The resulting Indian/West Pacific lineage suggests a possible invasion into the Indian Ocean from the West Pacific. This is the third polychaete reported from Wocan hydrothermal field. Among the three species, two includingP. miraandHesiolyra heteropoda(Annelida:Hesionidae) are present in high abundance, forming an alvinellids/hesionids-dominated polychaete assemblage distinct from that at all other Central Indian Ridge and Southwest Indian Ridge vents. Thus, this study expands our understanding of alvinellid biogeography beyond the Pacific, and adds to the unique biodiversity of the northern Indian Ocean vents, with implications for biogeographic subdivision across the Indian Ocean ridges.

Highlights

Deep-sea hydrothermal vents are extreme habitats rich in energy and reduced matters, which support flourished chemosynthesis-based ecosystems and form biodiversity hotspots along the global spreading ridge systems (Van Dover, 2000)
Hydrothermal vent organisms usually show a high degree of regional endemism (Rogers et al, 2012), a family endemic to the Pacific vents is still rare
We described a new species of Alvinellidae from northern Indian Ocean hydrothermal vent field and confirmed its placement in the genus Paralvinella using both morphological and genetic evidences

Summary

Introduction

Deep-sea hydrothermal vents are extreme habitats rich in energy and reduced matters, which support flourished chemosynthesis-based ecosystems and form biodiversity hotspots along the global spreading ridge systems (Van Dover, 2000). All of them are only known from Pacific hydrothermal vent fields, with the two Alvinella species (Alvinella pompejana Desbruyères and Laubier, 1980 and Alvinella caudata Desbruyères and Laubier, 1986) and three Paralvinella species (Paralvinella grasslei Desbruyères and Laubier, 1982, Paralvinella bactericola Desbruyères and Laubier, 1991 and Paralvinella pandorae irlandei Desbruyères and Laubier, 1986) reported from the East Pacific Rise (EPR) and Guaymas vent fields, four from the northeast Pacific (Paralvinella palmiformis Desbruyères and Laubier, 1986, Paralvinella pandorae pandorae Desbruyères and Laubier, 1986, Paralvinella dela Detinova, 1988 and Paralvinella sulfincola Desbruyères and Laubier, 1993), two from the southwest Pacific vent ecosystems (Paralvinella fijiensis Desbruyères and Laubier, 1993 and Paralvinella unidentata Desbruyères and Laubier, 1993), and one from the Marianas back-arc spreading center and the Okinawa Trough (Paralvinella hessleri Desbruyères and Laubier, 1989) These worms usually form dense aggregations on varied hard substrata, including chimney walls, basaltic cracks with venting fluids and siboglinid tubes (Tunnicliffe et al, 1993; Desbruyères et al, 1994; Hurtado et al, 2004). The view on this alvinellid biogeographic pattern is challenged by recent discovery of alvinellids in Indian Ocean vents

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