Identification of species of teatfish (Holothuroidea: Holothuriida) in Japan based on mitochondrial cytochrome oxidase subunit I (COI) sequences, morphology, and ossicles

Holothurians referred to as “teatfish” contain three species, Holothuria (Microthele) nobilis, H. (M.) whitmaei and H. (M.) fuscogilva, that have recently been included in CITES Appendix II for sustainable catch and trade. Taxonomic key traits of these species are primarily genetic sequences and there are few morphological differences among them, except for color patterns of the body. Although located in the northern limit of their distribution, there have been no reports identifying species of teatfish in Japan based on both morphology and genetic traits. This study investigated sequences of mitochondrial cytochrome oxidase subunit I (COI) and morphology including ossicles of black and white teatfish collected from Okinawa Island and Yaeyama Islands, Japan. The entirely black specimens and white specimens having black mottles on the dorsal side were identified as Holothuria (M.) whitmaei and H. (M.) fuscogilva, respectively, based on the agreement of genetic and morphological traits and with published data. There is no clear difference in COI sequences between specimens from Japan and other Pacific regions for both species. The only inconsistent finding with previous reports was that one specimen of H. (M.) whitmaei lacked Cuvierian tubules, which are usually present in this species, implying plasticity of this trait. Mean diameter of the disc and height of the pillars of table ossicles were shorter and longer, respectively, in H. (M.) fuscogilva than in H. (M.) whitmaei (p<0.05, t-test).