Two new and two rarely known species of Branchinotogluma (Annelida: Polynoidae) from deep-sea hydrothermal vents of the Manus Back-Arc basin, with remarks on the diversity and biogeography of vent polynoids

Abstract

The polynoid worms Branchinotogluma spp. are common and frequently abundant in deep-sea hydrothermal vents. They have the highest species diversity among the vent polynoids and various kinds of sexual dimorphism. Our investigation of polychaete specimens collected from deep-sea hydrothermal vents in the Manus Back-Arc Basin revealed four species of Branchinotogluma, including two new ones. These include Branchinotogluma segonzaci Miura and Desbruyères (1995); B. trifurcus Miura and Desbruyères (1995); B. pettiboneae sp. nov.; and B. ovata sp. nov. Branchinotogluma pettiboneae sp. nov. resembles B. tunnicliffeae (Pettibone, 1988), but can be distinguished from the latter by the reduced parapodia on segment 20 without notopodial lobes or notochaetae. Branchinotogluma ovata sp. nov. is most similar to B. elytropapillata Zhang et al., 2018, but differs from the latter in the structure of segment 19 in males, which is almost entirely wrapped inside segment 18 and invisible ventrally. The identities of the four species were well supported by genetic distance and phylogenetic analyses of the mitochondrial c oxidase subunit I (COI), 16S rRNA, 18S rRNA, and 28S rRNA genes. By combining reliable data on Branchinotogluma, Branchipolynoe, Lepidonotopodium, and Levensteiniella, the four most diverse polynoid genera occurring in hydrothermal vents, we evaluated their distribution pattern and delineated seven major hydrothermal biogeographic provinces worldwide. The Western Pacific harbors a higher species diversity of vent polynoids than the Eastern Pacific. Our analysis indicates that the Western Pacific is geographically complex and may have played an important role in the dispersal and speciation of vent polynoids.