SPECIES OF ASCOCOTYLE LOOSS, 1899 (DIGENEA, HETEROPHYIDAE) OF THE YUCATAN PENINSULA, MEXICO, AND NOTES ON THEIR LIFE-CYCLES

Heterophyid trematodes of the genus Ascocotyle Looss, 1899, metacercar iae of which were found in fish from freshwater (cenotes [sinkholes], lakes and the Rio Hondo River) and brackish coastal lagoons of the Pen insula of Yucatan, Mexico, are reviewed. The following species were fo und: Ascocotyle (Ascocotyle) tenuicollis Price, 1935; A. (A.) nunezae Scholz, Vargas-Vazquez, Vidal-Martinez & Aguirre-Macedo, 1996; A. (A.) chandleri Lumsden, 1963; A. (Phagicola) nana Ransom, 1920; A. (P.) di minuta Stunkard & Haviland, 1924; A. (P.) macrostoma (Robinson, 1956); and A. (Leighia) megalocephala Price, 1932. Descriptions of metacerca riae and adults from naturally and experimentally infected hosts are p rovided. Considerable variation was found in the number(18-22) and arr angement of circumoral spines of A. (P.) nana: most specimens (70%) ha d 20 spines arranged in one complete row of 16 spines and four additio nal spines dorsally, which differs from the arrangement of circumoral spines in the type-series of this species. In contrast, spination patt erns of A. (A.) tenuicollis (16 + 16 spines in two rows) and A. (P.) d iminuta (16 + 2) were constant. The validity of A. (P.) diminuta and A . (P.) nana, species recently resurrected from synonymy with A. (P.) a ngrense Travassos, 1916, was confirmed. Except for A. (A.) tenuicollis , all species are reported from Mexico for the first time. The heron C asmerodius albus represents a new definitive host of adults of all the above-mentioned species excluding A. (A.) chandleri. A key to the ide ntification of Ascocotyle metacercariae occurring in fishes of the Yuc atan Peninsula is also provided.