Acricoactis brachyacontis sp. nov. from Adak Island, Alaska, represents a new genus and family of metridioidean sea anemone (Anthozoa: Hexacorallia: Actiniaria)

Abstract

Acricoactis brachyacontis sp. nov. is described based on specimens collected from Adak Island (Aleutian Islands, Alaska, USA). This acontiate sea anemone lacks a marginal sphincter, has only basitrichs in the acontia, and has six pairs of complete mesenteries, thus falling outside any existing family diagnosis. Nucleotide sequences from four gene regions (12S, 16S, 18S, COIII) corroborate the morphological finding, placing the sequenced individuals as sister to, rather than nested within, any existing monophyletic family. The new species therefore represents a new family, Acricoactinidae, as well as a new, monospecific genus. In spite of the lack of a marginal sphincter, individuals may fully retract and cover their tentacles through the contraction of the regular circular muscles in the distal region of the column. Various features of Acricoactinidae are shared with cuticulate species (e.g., with only one cycle of complete mesenteries, reduced acontia, and a few perfect mesenteries) and acuticulate species (e.g., with smooth, thin column, and a shallow water distribution), but molecular data presented here place the family within the clade Acuticulata.