A new species of Erinaceusyllis (Annelida: Syllidae) discovered at a wood-fall in the eastern Clarion-Clipperton zone, central Pacific ocean

In the deep sea, organic falls provide temporary localized enrichments of organic matter to the otherwise nutrient-poor abyssal seafloor. Areas where organic falls land become ephemeral patches of increased biodiversity. Often rich in opportunistic species which are tolerant to the sulfidic environment formed from anaerobic breakdown of organic matter. On a wood-fall at abyssal depths in the eastern Clarion-Clipperton Zone, the novel species Erinaceusyllis simonlledoi (Annelida: Syllidae) was discovered in high abundance. This study entails the first description of a novel syllid species found in high density on a naturally occurring organic fall. Phylogenetic position was investigated using three genetic markers (16S, 18S, COI) and morphology was studied through light- and scanning electron microscopy. Genetic data and morphological analysis supported placement in the syllid genus Erinaceusyllis . Distinguishing features were lack of eyes, dorsal brooding of one egg per egg-bearing segment, lack of visible papillae across the body, incomplete fusion of palps, bidentate chaetae, as well as pyriform antennae and tentacular cirri. Erinaceusyllis simonlledoi sp. nov. is highly similar to a species found on hydrothermal vents belonging to the closely related genus Sphaerosyllis . The similarity between the two species, as well as findings of unspecified Sphaerosyllis species in various types of sulfidic habitats evoke questions of a possible syllid lineage adapted to sulfidic environments. • A novel polychaete species was discovered on an abyssal wood-fall. • Its high abundance on degraded wood displays a tolerance to sulfidic environments. • Morphology and genetics support placement in Erinaceusyllis of the family Syllidae. • This constitutes the first finding of abundant syllids on a natural wood-fall. • Sulfide-tolerant syllids in the East Pacific may originate from the same lineage.