biostudies-literatureUnknown918Tsuyuki AWe describe a new species of polyclad flatworm, <i>Enchiridium daidai</i> <b>sp. nov.</b>, from the rocky subtidal zone in the East China Sea along the coasts of the Kyushu and Okinawa Islands, Japan. <i>Enchiridium daidai</i> <b>sp. nov.</b> is characterized by i) the entire periphery of the dorsal surface narrowly fringed with orange, ii) a marginal-eyespot band extending to the position of the mouth (about anterior one-eighth of body), and iii) two prostatic vesicles covered by a common muscle sheath, which is penetrated by the ejaculatory duct. We performed a molecular phylogenetic analysis based on 945-bp 28S rDNA sequences of 16 species of Prosthiostomidae currently available in public databases in addition to those of <i>E. daidai</i> <b>sp. nov.</b> and <i>Prosthiostomum torquatum</i> Tsuyuki et al., 2019. In the resulting tree, our new species was nested in a clade composed of <i>Enchiridium</i> species. The tree topology was in favor of a taxonomic view that <i>Enchiridium</i> should be defined by having i) a common muscle sheath that encloses two prostatic vesicles and ii) marginal eyespots that may or may not surround the periphery of the dorsal surface.ZooKeys15-28https://www.ebi.ac.uk/biostudies/studies/S-EPMC7082371biostudies-literatureA giant new species of <i>Enchiridium</i> (Polycladida, Prosthiostomidae) from southwestern Japan.PMC7082371Tsuyuki AKajihara HfalseA giant new species of <i>Enchiridium</i> (Polycladida, Prosthiostomidae) from southwestern Japan.We describe a new species of polyclad flatworm, <i>Enchiridium daidai</i> <b>sp. nov.</b>, from the rocky subtidal zone in the East China Sea along the coasts of the Kyushu and Okinawa Islands, Japan. <i>Enchiridium daidai</i> <b>sp. nov.</b> is characterized by i) the entire periphery of the dorsal surface narrowly fringed with orange, ii) a marginal-eyespot band extending to the position of the mouth (about anterior one-eighth of body), and iii) two prostatic vesicles covered by a common muscle sheath, which is penetrated by the ejaculatory duct. We performed a molecular phylogenetic analysis based on 945-bp 28S rDNA sequences of 16 species of Prosthiostomidae currently available in public databases in addition to those of <i>E. daidai</i> <b>sp. nov.</b> and <i>Prosthiostomum torquatum</i> Tsuyuki et al., 2019. In the resulting tree, our new species was nested in a clade composed of <i>Enchiridium</i> species. The tree topology was in favor of a taxonomic view that <i>Enchiridium</i> should be defined by having i) a common muscle sheath that encloses two prostatic vesicles and ii) marginal eyespots that may or may not surround the periphery of the dorsal surface.2020-01-01T00:00:00Z20202024-11-06T13:02:39.066Z2020-05-22T14:34:42ZS-EPMC70823713221066310.3897/zookeys.918.47061