Species of Ascocotyle Looss, 1899 (Digenea: Heterophyidae) of the Yucatan Peninsula, Mexico, and notes on their life-cycles.
Heterophyid trematodes of the genus Ascocotyle, metacercariae of which were found in fish from freshwater (cenotes (sinkholes), lakes and the Río Hondo River) and brackish coastal lagoons of the Peninsula of Yucatan, Mexico, are reviewed. A total of 707 fish of 21 species were examined between September 1993 and January 1995. Fish-eating birds (3 species) were examined in December 1987 and January 1988. The following species were found: Ascocotyle (Ascocotyle) tenuicollis; (A. (A.) nunezae; A. (A.) chandleri; A. (Phagicola) nana; A. (P.) diminuta; A. (P.) macrostoma; A. (Leighia) megalocephala. Descriptions of metacercariae and adults from naturally- and experimentally-infected hosts are provided. Considerable variation was found in the number (18-22) and arrangement of circumoral spines of A. (P.) nana: most specimens (70%) had 20 spines arranged in one complete row of 16 spines and 4 additional spines dorsally, which differs from the arrangement of circumoral spines in the type-series of this species. In contrast, spination patterns of A. (A.) tenuicollis (16 + 16 spines in 2 rows) and A. (P.) diminuta (16 + 2) were constant. The validity of A. (P.) diminuta and A. (P.) nana, species recently resurrected from synonymy with A. (P.) angrense, was confirmed. Except for A. (A.) tenuicollis, all species are reported from Mexico for the first time. The heron Casmerodius albus represents a new definitive host of adults of all the above-mentioned species except A. (A.) chandleri. A key to the identification of Ascocotyle metacercariae occurring in fishes of the Yucatan Peninsula is also provided.