The first record of ring sea anemones from the Saudi Arabian Red Sea mesophotic zone

Abstract Ring sea anemones (Cnidaria, Actiniaria) engage in symbiotic associations with octocorals by attaching to their branches and surrounding them with tissue junctions, causing a significant reduction of the host’s coenenchyme. They have previously been reported from the North Atlantic, Western Indian, and Pacific Oceans, from 30 m to aphotic depths, colonising species of sea fans and sea pens in potentially parasitic relationships. Here, we report the first record of ring sea anemones from the Saudi Arabian Red Sea mesophotic waters, living on an octocoral host of the family Ellisellidae at 97 m depth. Through morphological and phylogenetic analyses based on the sequencing of the 12S small subunit rRNA region, we confirmed the identification of these ring sea anemones as Peronanthus sp. (Actiniaria, Amphianthidae). While expanding our knowledge on the geographic range of this genus, this finding emphasises the importance of explorations of coral-associated fauna at mesophotic depths, to better understand their diversity, their relationships with their hosts, and their potential ecological roles within these ecosystems.