Occurrence of the subgenus Acanthosentis Verma & Datta, 1929 (Acanthocephala: Quadrigyridae) in Japan, with the description of Acanthogyrus (Acanthosentis) alternatspinus n. sp. and A. (A.) parareceptaclis n. sp. from Lake Biwa drainage fishes and a key to the species of the subgenus.

All 44 described species of the subgenus Acanthosentis Varma & Datta, 1929 are recognised as valid. These include two new species, Acanthogyrus (Acanthosentis)alternatspinus n. sp. from Rhodeus ocellatus ocellatus (Kner) (Cyprinidae) and A. (A.) parareceptaclis n. sp. from Cobitis biwae Jordan & Snyder (Cobitidae) in the Lake Biwa drainage, Japan. These are the first representatives of the subgenus Acanthosentis recorded from Japan. Most other species are found in the Indian subcontinent, but a few have been reported from China, elsewhere in Asia, Africa, Europe and Central America. Only A. (A.) alternatspinus has the lateral proboscis hooks in the apical and middle circles markedly displaced posteriorly but of equal size to the other hooks in the same circles and multi-branched lemnisci. Acanthogyrus (A.) parareceptaclis uniquely possesses parareceptacle structures in both sexes as well as a pair of cone-shaped genital jackets flanking the vagina (vaginal sleeve). Two new names are provided: Acanthogyrus (Acanthosentis) adriaticus nom. nov. for A. (A.) lizae Orecchia, Paggi & Radujkovic, 1988 nec Wang, 1896, and A. (A.) cheni nom. nov. for A. (A.) coiliae (Yamaguti) sensu Chen et al. (1973). A review of the species composition of Acanthosentis is provided and a key to its species and zoogeographical notes are included.