Parazoanthidae (Cnidaria, Zoantharia) associated with glass sponges on the Nishi-Shichito Ridge, northwestern Pacific Ocean, with the description of a new species.

Seamounts are biodiversity hotspots that face increasing threats from anthropogenic activities. Seamounts host diverse sessile suspension-feeding organisms such as sponges and anthozoans, which are crucial for seamount ecosystems as they construct three-dimensional habitats utilized by numerous other animals. Therefore, accurate identification of seamount fauna, in particular of sessile suspension-feeding organisms, is of paramount importance for robust conservation efforts. This study focused on Zoantharia, a sessile anthozoan group, and specifically the family Parazoanthidae, known for associations with many different host taxa, prominently including octocorals and sponges. We collected Parazoanthidae specimens from northwestern Pacific seamounts and formally describe a new species, Vitrumanthusflosculus Kise & Reimer, sp. nov., based on morphological and molecular analyses. We also report the complete mitochondrial genomes of this new species and the related species Churabanakuroshioae. Our results reconfirm the phylogenetic positions of these two species within Parazoanthidae, while demonstrating much remains to be learned about the benthic diversity of northwestern Pacific seamounts.