Two sea anemones (Cnidaria: Anthozoa: Actiniaria) from the Southern Ocean with evidence of a deep-sea, polar lineage of burrowing sea anemones

Abstract

Abstract Hexacorals are important components of macrobenthic communities in the Southern Ocean, dominating Antarctic continental shelves. Most of the 119 sea anemones recorded for the Southern Ocean are endemic (81% and 25% endemic species and genera, respectively, one endemic family) with only two species extending beyond the limits of the Southern Ocean. Over 70% of the 83 genera in the Southern Ocean are monotypic, including half of the generic diversity in superfamily Actinostoloidea, which suggests that Antarctica has been isolated long enough for the evolution of new genera but not for many families to evolve. Here, we describe Chitinactis marmara gen. & sp. nov., a new monotypic actinostoloidean genus from Antarctica diagnosed by its unique bi-layered cuticle on column, hexamerous symmetry, unequal development of younger mesenteries and mesogleal tentacle musculature. We also re-describe and extend the geographic distribution of Scytophorus striatus, another endemic Antarctic species. Based on morphological and molecular data, we establish the phylogenetic position of C. marmara and discuss the implications of the phylogenetic position of S. striatus for the resurrection and circumscription of the family Halcampoididae and the evolution of burrowing sea anemones. Finally, we discuss evidence for an actinostoloidean deep-sea, polar lineage of burrowing sea anemones.