CALIXOLEPIS THULI N. G., N. SP. (CESTODA, HYMENOLEPIDIDAE) FROM THE WOOD DUCK AIX SPONSA (ANATIDAE) IN AMERICA

Calixolepsi thuli n. g. n. sp. is described and figured on the basis o f the specimens from the wood duck Air sponsa (L.) (Anseriformes: Anat idae) from Cuba and the USA. The tapeworm is characterised by: (1) str obila of medium size; (2) deep genital atrium; (3) external accessory sac; (4) unilateral genital pores, with female genital ducts situated anterior to male ducts; and (5) the following characteristic structure of the male and female terminal genitalia: the genital pouch has a st ylet and a goblet-like structure, the calix; a cirrus is absent; and t he thick-walled copulatory part of the vagina forms vaginal vestibule distally which may open through a vaginal papilla into the genital atr ium. Other morphological structures indicate a relationship with speci es of the genus Sobolevicanthus Spasskii & Spasskaya, 1954 or with Cla dogynia Baer, 1938 (Hymenolepididae). The differences between the tape worms from Cuba and the USA suggest the possible occurrence of various morphological forms of Calixolepis.