New host crab Macrophthalmus (Macrophthalmus) convexus Stimpson, 1858 of the endangered pedunculate barnacle Octolasmis unguisiformis Kobayashi & Kato, 2003 (Lepadomorpha: Poecilasmatidae) in Amami Oshima Island, Japan

The pedunculate barnacle Octolasmis unguisiformis is a rare epibiotic barnacle attached to a macrophthalmid crab, Macrophthalmus (Macrophthalmus) milloti Crosnier, 1965, on tidal flats in the Ryukyu Archipelago. It has a rare sexual system called androdioecy, a coexistence of hermaphrodites and males in the population. In June 2020, we found two hermaphrodites and one dwarf male of O. unguisiformis attached to a female M. (M.) convexus at Kise Bay, Amami Oshima Island. Here we describe the symbiotic conditions between the pedunculate barnacle and the new host crab species.