Description of two new species of Neotachidius Shen & Tai, 1963 (Copepoda, Harpacticoida, Tachidiidae) from Korean brackish waters and proposal of a new genus for Tachidius (Tachidius) vicinospinalis Shen & Tai, 1964

Abstract

Two new sympatric species of Neotachidius Shen & Tai, 1963, N. coreanus sp. nov. and N. parvus sp. nov., are described from plankton samples collected from brackish waters in Kwangyang Bay, South Korea. Morphological differences with the type species N. triangularis (Shen & Tai, 1963) comb. nov. are discussed in detail. Korean material from Chindo Island, previously identified as N. triangularis by Song and Chang in 1995 is at least partly based on N. parvus sp. nov. The occurrence of N. triangularis in estuaries in British Columbia and Washington is attributed to transoceanic transport by ballast water from cargo ships entering the Columbia River or neighbouring estuaries. The subgeneric division of the genus Tachidius proposed by Shen and Tai in 1963 is rejected and instead full generic rank is assigned to both Tachidius and Neotachidius. The taxonomic position and original description of Tachidius (Tachidius) vicinospinalis Shen & Tai, 1964 are reviewed and the species is designated as the type species of a new genus Sinotachidius gen. nov. The latter and Neotachidius form a clade which stands in apposition to Tachidius. Tachidius discipes Giesbrecht, 1881 sensu Song & Chang is considered species inquirenda in Sinotachidius gen. nov..