Lamellodiscus chin n. sp. (Monogenea: Diplectanidae) was described from Acanthopagrus sivicolus Akazaki (Perciformes: Sparidae) in Okinawa-jima Island, Ryukyu Islands based on morphological and molecular data. This new species resembles L. spari and L. elegans in morphologically but differs by its accessory piece curving and widening toward the tip. Three species of Lamellodiscus (L. japonicus Ogawa & Egusa, 1978, L. takitai Ogawa & Egusa, 1978, and L. spari Zhukov, 1970) were recorded from A. schlegelii (Bleeker), and L. japonicus was collected from A. latus (Houttuyn) in the Seto Inland Sea, Japan. I herein propose Lamellodiscus egusai nom. nov. for L. japonicus which is a junior primary homonym of L. japonicus Pillai & Pillai, 1974. Based on the type specimens and newly collected specimens from wild hosts, the type localities of L. japonicus (= L. egusai nom. nov.) and L. takitai are discussed. In addition, a list of nominal species of Japanese diplectanids is provided. Keywords Platyhelminthes Á Type locality Á New species Á Principle of homonymy This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as 4F68D660-9603-4B63-8EA9-26A5E884C7E5. This article was published as an Online First article on the online publication date shown on this page. The article should be cited by using the doi number. This is the Version of Record.