A new deep-water Actiniaria species, Isanthus homolophilus sp. nov. is described from the French Polynesia. Morphological and ecological differences between the new species and the other known species of the genus Isanthus are discussed. The distinct morphological characteristics that distinguish I. homolophilus, are the presence of a tentaculated columnar margin, the tentacle number (84–96), and its cnida biometry. A further ecological characteristic is the distinct symbiotic relationship that the anemone exhibits towards the decapod Hypsophiys inflata.
During the biological researches of the ‘Service Mixte de Contrôle Biologique’ (SMCB) in French Polynesia (1986–1990) at depths ranging from 100 to 1120 m, a symbiotic association between a deep-water homolid crab, Hypsophrys inflata Guinot & Richer de Forges, 1981 and a sea anemone of the genus Isanthus (Actiniaria: Isanthidae) was collected. Even though this association was described by Guinot et al. (1995) and Chintiroglou et al. (1996), no concise description of the anemone is given. Thus, the goal of the present study was to provide a detailed description of the new anemone species and compare it with other species of the Isanthidae Carlgren, 1938 family.
The methodology followed in our investigation was that of Doumenc & Foubert (1984) and Doumenc et al. (1985). Nematocyst nomenclature used was as proposed by England (1991). Abbreviations: MNHN (Museum National d'Histoire Naturelle Paris).