Helminths from the giant mottled eel Anguilla marmorata Quoy & Gaimard in Japan, with a description of Acanthocephalus longiacanthus n. sp. (Acanthocephala: Echinorhynchidae).

Five helminths, including a new echinorhynchid acanthocephalan Acanthocephalus longiacanthus n. sp., are described based on specimens from the giant mottled eel Anguilla marmorata Quoy & Gaimard caught in a small river, western Japan. The new acanthocephalan is distinguished from the other congeners in terms of hook arrangement (8-9 longitudinal rows with 5-6 hooks per row) on proboscis, maximum length of hook blade (81-95 μm in male, 150-190 μm in female), lemnisci being longer than proboscis receptacle, and small-sized eggs (80-83 μm). Two monogeneans, Pseudodactylogyrus anguillae (Yin & Sproston, 1948) and P. bini (Kikuchi, 1929), and two acanthocephalans, Acanthocephalus gotoi Van Cleave, 1925 and Southwellina hispida (Van Cleave, 1925), were also found; this new material is described. The monogeneans are notorious as invasive parasites spreading worldwide via anthropogenic transportations of anguillid eels, but in Japanese waters A. marmorata appears to be an indigenous host for these parasites. Anguilla marmorata is a new host record for the acanthocephalans A. gotoi and S. hispida.