A new zoantharian: Sphenopus exilis

Credit: Takuma Fujii

Zoantharians are colonial cnidarians commonly found in a variety of marine environments. Many of them live in the shallow waters of the subtropical and tropical regions, where their large colonies can be found on coral reefs.

There are very solitary zoantharian species. Only three species are described, all reported more than 100 years ago from the Indo-Pacific region. Today's species, named Sphenopus exilis, is much smaller than the other three species and currently only known from two bays on the east coast of Okinawa Island. Its name was derived from the latin word exilis meaning slender or small, as polyps have an elongate and narrow foot.

For the experts: A new species of free-living solitary zoantharian is described from Okinawa, Japan. Sphenopus exilis sp. n. occurs on silty seafloors in Kin Bay and Oura Bay on the east coast of Okinawa-jima Island. Sphenopus exilis sp. n. is easily distinguished from other Sphenopus species by its small polyp size and slender shape, although there were relatively few differences between Sphenopus exilis sp. n. and S. marsupialis in the molecular phylogenetic analyses. Currently, very little is known about the ecology and diversity of Sphenopus species. Thus, reviewing each species carefully via combined morphological and molecular analyses by using newly obtained specimens from type localities is required to clearly understand and distinguish the species within the genus Sphenopus.