Stephanthus antarcticus, a new genus and species of sea anemone (Actiniaria, Haloclavidae) from the South Shetland Islands, Antarctica

Abstract

Stephanthus antarcticus gen. nov. et sp. nov. is described and illustrated from six specimens collected in the Antarctic Peninsula on the Polarstern cruises ANT XV/3 and ANT XIX/3. The new genus is characterised by the absence of sphincter and basilar musculature, the presence of a single strong siphonoglyph with a basal enlargement, distinct parietobasilar musculature, tentacles without acrospheres, two cycles of six pairs of mesenteries (only one of them perfect), and a deep fosse with parapet; another remarkable feature is the absence of microbasic p-mastigophores. The new genus shows characteristics of three families of soft-bottomdwelling sea anemones, namely Haloclavidae Verrill, 1899, Halcampoididae Appellöf, 1896, and Andresiidae Stephenson, 1922. The generic characters of Stephanthus gen. nov. are discussed and it is tentatively placed in the family Haloclavidae.