Hidden diversity of Freyastera (Asteroidea, Brisingida, Freyellidae) at great depth: Description of new species and remarks on species boundaries

Freyastera represents the most derived form in the deep-sea starfish order Brisingida, known only at below 2500 m to over 6000 m depth, adapting to the great depth by small body size, reduced number of arms, and simplified body form. Long being remote and rarely investigated, newly collected specimens from the last decade revealed high species diversity of the genus. In this study, a new species, Freyastera jiaolongi sp. nov., is described from the southern part of the Kyushu-Palau Ridge.

Freyastera giardi comb. nov. and Freyastera loricata comb. nov., formerly belonging to genus Freyella, are reassigned to Freyastera. The genus is hence revised to include ten species. Key characters of nine Freyastera species as well as Freyella benthophila (formerly Freyastera benthophila) are described and discussed based on an examination of type specimens and new specimens, and a key to Freyastera species is provided, aiding in the future identification of Freyastera.

Phylogenetic analysis using four DNA barcoding genes retrieves a monophyletic Freyastera, providing solid support for interspecific phylogeny except at three nodes. Species delimitation analysis results in 11 species units within Freyastera, including seven unnamed species pending description. A high diversity of Freyastera revealed in the present study suggests a successful adaptation and radiation of the genus at great depth.