The ‘Shinkai Seep Field’ is a serpentinite-hosted chemosynthetic ecosystem in the Southern Mariana Forearc. In June 2015 the site was revisited and a number of rissoiform gastropods were collected. Taxonomic investigations revealed that these specimens represent a hitherto undescribed species of Provanna (Gastropoda: Abyssochrysoidea), described herein as Provanna cingulata n. sp. This new species is characterized by numerous spiral keels, lack of significant axial sculpture, rounded and inflated whorls, and large size for the genus. With the shell height exceeding 16.5 mm (may reach 20 mm), it is the largest Provanna species known thus far. Phylogenetic analysis using 411 bp of the cytochrome oxidase c subunit I (COI) gene confirmed its systematic placement within the genus Provanna. This is the only gastropod from a family endemic to chemosynthetic ecosystems thus far known from the ‘Shinkai Seep Field’. Furthermore, with a collection depth of 5687 m, it represents the deepest known bathymetric range for the superfamily Abyssochrysoidea as a whole.

Vestimentiferan tubeworms are significant members of deep-sea chemosynthetically-driven communities, including hydrothermal vents and cold seeps. The reproductive condition in this taxon is rarely studied because of sampling constraints inherent to these environments, and the lack of a simple methodology to quantify gonad development in vestimentiferans.

We demonstrate that the amount of gonad found in the first 10 mm of trunk can be used as representative of the reproductive condition of the individual, and we establish a linear relationship between the amount of gonad and the proportion of wax ester in the trunk of female vestimentiferans. This relationship represents a new method for the determination of the reproductive condition in this group.