An unusual sea anemone from slope depths of the tropical west Pacific: range extension and redescription of Isactinernus quadrilobatus Carlgren, 1918 (Cnidaria: Actiniaria: Actinernidae)

The sea anemone species Isactinernus quadrilobatus Carlgren, 1918, and Synactinernus flavus Carlgren, 1918, which were described in new monotypic genera from few specimens collected in southern Japan, are synonymized, based on many more specimens from the South Pacific. As well as the geographic range, the depth range of this species has been extended to 110-700 m. The species had been distinguished primarily on whether the oral disc had four lobes (I. quadrilobatus) or eight (Synactinernus flavus) – we conclude their number is largely related to size of the animal. Other features that Carlgren had used to differentiate the genera (and species) are inconsistently present and do not correlate with lobe number.