Integrative taxonomy of two new peltospirid gastropods from Mid-Atlantic Ridge hot vents, including a potentially symbiotic species

Deep-sea hydrothermal vents host lush communities of animals relying on bacterial chemosynthetic primary production, where intimate symbioses often form. Peltospiridae are a family of gastropods endemic to hot vents, whose members exhibit a variety of feeding strategies ranging from bacterial grazing to total reliance on endosymbiosis. Here, we report and describe two new peltospirid snails, Peltospira gargantua sp. nov. and Lirapex pantagruel sp. nov., from two recently discovered vent fields on the Mid-Atlantic Ridge. Peltospira gargantua is clearly distinct from other congeners by its much larger size, differences in the number and arrangement of epipodial tentacles, and notably, a hypertrophied oesophageal gland. Lirapex pantagruel is also the largest known species in the genus, differing from other species also by shell shape and sculpture. Phylogenetic reconstructions using the mitochondrial cytochrome c oxidase subunit I (COI) gene agree with their respective generic placements. An expanded oesophageal gland in peltospirids was known only from the endosymbiotic genera Chrysomallon and Gigantopelta, where it is used to host symbionts, indicating that P. gargantua is probably also endosymbiotic. This would represent another case of likely convergently acquired oesophageal endosymbiosis in the family, and the first record of endosymbiotic gastropod from Mid-Atlantic Ridge vents.