On the Occurrence of the Invasive Freshwater Limpet Ferrissia californica (Mollusca: Gastropoda: Planorbidae) in Japan.

Two members of the genus Ferrissia Walker, 1903, namely Ferrissia nipponica (Kuroda, 1949) and F. japonica Habe and Burch, 1965, have been reported to occur in Japan, but due to a lack of molecular data, doubts have been expressed as to their validity. Furthermore, the possible presence of allochthonous Ferrissia taxa has been stated under a variety of names, so that even now there is no consensus on their presence and identity. Recently, freshwater limpets belonging to the planorbid genus Ferrissia were collected in an irrigation trough on the Izu island of Hachijōjima, Tokyo, Japan. Molecular identification of the collected specimens, based on a fragment of the large ribosomal subunit 16S (mtDNA), unequivocally proved that they belong to the allochthonous, invasive species Ferrissia californica (Rowell, 1863), the protagonist of a relentless cryptic invasion worldwide to which can Japan can now be added. The shells of the collected specimens show some scars, which bear testimony to the fragile nature of the shell and, possibly, to the paucity of calcium in the inland waters of Hachijōjima.