Helicoductus thulakoceras n. g., n. sp. (Cestoda: Hymenolepididae) a parasite of Charadrius marginatus (Aves: Charadrii) from South Africa.

The authors describe and illustrate Helicoductus thulakoceras n. g., n. sp., a parasite of Charadrius marginatus (Aves: Charadrii) from South Africa. This hymenolepidid cestode is 1.5-3 mm long, with a rostellum armed with 10 diorchoid hooks 75-80 microm long (mean 77 microm) and anomalous terminal genital ducts. One spine (10-15 microm long) is inserted at the ventral extremity of the male genital pouch. An invaginated cirrus is absent. A non-retractable and non-invaginable external tube, 25-30 x 4-2.5 microm, appears as a spiral, sclerotinised, spinous canal, which is non-retractable, non-invaginable and directed dorso-ventrally from the genital pouch to a second ventral canal parallel with the male genital pouch; the second canal is thin and spine-like (15-20 x 1.5 microm) with a thick hyaline muff. These peculiar anatomical structures are discussed. They are considered to justify the erection of a new genus.