Stylobates birtlesi sp. n., a new species of carcinoecium-forming sea anemone (Cnidaria, Actiniaria, Actiniidae) from eastern Australia

Abstract. We describe a new species of carcinoecium-forming sea anemone, Stylobates birtlesi sp. n., from sites 590–964 m deep in the Coral Sea, off the coast of Queensland, Australia. An anemone of this genus settles on a gastropod shell inhabited by a hermit crab, then covers and extends the shell to produce a chitinous structure termed a carcinoecium. Stylobates birtlesi sp. n. is symbiotic with the hermit crab Sympagurus trispinosus (Balss, 1911). The nature of marginal sphincter muscle and nematocyst size and distribution distinguish Stylobates birtlesi sp. n. from other species in the genus. The four known species of Stylobates are allopatric, each inhabiting a separate ocean basin of the Indo-West Pacific. We also extend the known range of Stylobates loisetteae in the Indian Ocean off the coast of Western Australia.