Zoanthids are a group of corals that live on coral reefs, the deep sea and many other marine environments around the world. Members of the genus Epizoanthus are generally found in association with other marine invertebrates such as hermit crabs, tubeworms, and gastropods.
Some zoanthids contain the substance palytoxin. Palytoxin is one of the most toxic organic substances in the world. Even in small quantities, the toxin can be fatal should it be ingested or enter the blood stream.
One new species, Epizoanthus inazuma, forms colonies resembling a classic lightning-bolt shape, hence it has been given a name meaning 'lightning' in Japanese. The second new species is also named in reference to its lifestyle as it bears the name of the local Palauan folklore character Beriber, who lived in a cave.
For the experts: Epizoanthus species are generally found in association with other marine invertebrates such as hermit crabs and gastropods. Although Epizoanthus spp. are relatively common, there is limited information about their diversity and ecology due to their habitats or hosts, often being below the depths of SCUBA diving (>~50 m). In particular, the Epizoanthus fauna of the Indo-Pacific Ocean remains poorly understood. In this study, the diversity of Epizoanthus species associated with eunicid worm tubes from shallow waters in the Pacific Ocean we investigated using molecular analyses (mitochondrial cytochrome oxidase subunit 1 = COI, mitochondrial 16S ribosomal DNA = mt 16S-rDNA, nuclear internal transcribed spacer region of ribosomal DNA = ITS-rDNA) combined with morphological and ecological data. The combined data set leads us to describe two new species; Epizoanthus inazuma sp. n. and Epizoanthus beriber sp. n. Both new species are found in low-light environments: E. inazuma sp. n. on mesophotic coral reef slopes and reef floors, or on the sides of overhangs; E. beriber sp. n. has only been found in caves. Morphological characteristics of these two new species are very similar to E. illoricatus Tischbierek, 1930 but the two new species are genetically distinct. Mesentery numbers and coloration of polyps may be useful diagnostic characteristics among eunicid-associated Epizoanthus species. These results demonstrate that there is high potential for other potentially undescribed zoantharian species, particularly in underwater cave habitats.