First record of tropical sea urchin <i>Echinometra</i> sp. C from Honshu, Japan

Between 2013 and 2017, we collected 30 sea urchins that belonged to the genus Echinometra from Banshozaki Cape, Shirahama, Wakayama, Japan. These specimens included 6 greenish individuals that resemble Echinometra. sp. C (reported by Arakaki et al., 1998), a species distributed in only Okinawa and southwards. Molecular analysis based on partial sequences of the mitochondrial cytochrome oxidase subunit I gene (1,080 bp) suggested that the 30 sea urchins from Shirahama were Echinometra mathaei, Echinometra oblonga, Echinometra sp. A. and Echinometra sp. C. Five of the 6 greenish specimens were genetically identical to Echinometra sp. C from Okinawa. Triradiate spicules present in the gonads, a diagnostic character of Echinometra sp. C., further confirmed the taxonomy of the 5 individuals. The remaining green specimen was identified as Echinometra mathaei on the basis of both molecular analysis and spicule morphology. To the best of our knowledge, this is the first record of Echinometra sp. C on the main island of Japan (Honshu). Here, we have discussed the reasons for the emergence of tropical sea urchins around Banshozaki Cape, Shirahama.