Further records of introduced Semisulcospira snails in Japan (Mollusca, Gastropoda): implications for these snails’ correct morphological identification

Abstract

Seven species of the freshwater snail genus Semisulcospira, which are indigenous taxa of the largest lake in Japan, Lake Biwa, have been introduced into 17 localities, including five newly recorded localities. Among these species, S. dilatata Watanabe and Nishino, 1995, S. habei Davis, 1969, and S. rugosa Watanabe and Nishino, 1995 were firstly recorded as introduced species. The alien Semisulcospira snails could be identified based on the combination of three morphological characters: longitudinal ribs number of penultimate whorl of adult shell, spire angle of adult shell, and shell height of the largest embryonic shell. Accordingly, morphological identification of introduced Semisulcospira populations recorded in previously published studies was revisited. The introductions of Semisulcospira snails have been suggested to have occurred due to contamination of seedlings of other shellfish and fishes at most sites. Taking into account the potential impacts of accidental species introductions, seedlings should be carefully managed so as not to unintentionally introduce Semisulcospira snails.