Abstract
A new monorchiid digenean, Lasiotocus chichibu sp. n., is described from the intestine of a brackish water goby, Tridentiger obscurus (Temmink and Schlegel) in the estuaries of the Tsurumi and Jiju River in Kanagawa Prefecture, Japan. This species is distinguished from most closely related species, L. lintoni (manter, 1931) Hopkins, 1941, L. longovatus (Hopkins, 1941) Thomas, 1959 and L. parvus (Manter, 1931) Yamaguti, 1954 by position of the terminal organ, egg size, shpe of oral sucker and number of ovarian lobes. This is the forth species of the genus Lasiotocus from fishes of Japan.
Key words: Digenea; Monorchiidae; Lasiotocus chichibu sp. n.; Tridentiger obscurus; Japan.