Examination of 4055 molluscs of 10 species from cenotes (= sinkholes) and other freshwater bodies in the Yucatan Peninsula, Mexico revealed the presence of-larval stages of 13 trematodes. The following species were found: Echinochasmus leopoldinae Scholz, Ditrich et Vargas-Vázquez, 1996, E. macrocaudatus Ditrich, Scholz et Vargas-Vázquez, 1996 (Echi-nostomatidae), Saccocoelioides sp. (? sogandaresi Lumsden, 1963) (Haploporidae), Crassicutis cichlasomae Manter, 1936, pleurolophocercous ophthalmocercaria sp. (Homalometridae), Ascocotyle (Ascocotyle) sp., Ascocotyle (Phagicola) nana Ransom, 1920 (Heterophyidae), Oligogonotylus manieri Watson, 1976 (Cryptogonimidae), Genarchella astyanactis (Watson, 1976) (Derogenidae), xiphidiocercariae sp. 1, 2 and 3 (Lecithodendriidae?), and furcocercaria gen. sp. (Fellodistomidae). The life-cycle of the derogenid Genarchella astyanactis was studied for the first time. It was found that it differs from that of G. genarchella: the first intermediate host, Pyrgophorus coronatus (Pfeiffer, 1839), released cystophorous furcocercariae of G. astyanactis that developed, after ingestion by the second intermediate host, copepods (experimentally Mesocyclops chaci Fiers, Reid, Ilife et Suárez-Morales, 1996), into metacercariae resembling by their morphology juvenile trematodes found in the stomach of Aslya-nax fasciatus. No progenetic cercariae (metacercariae) found in G. genarchella were observed in the life-cycle of G. astyanactis. Rediae and cystophorous furcocercariae were recovered from naturally infected snails and snails experimentally kept in contact with eggs from the uterus of G. astyanactis adults.
The paper presents a survey of the metacercariae of trematodes found in 581 fishes of 15 species from 39 cenotes (sinkholes) of the Yucatan Peninsula, southeastern Mexico. The following 21 species were found: Echinochasmus sp. 1, Echino-chasmus sp. 2, Echinostomatinae gen. sp. (family Echinostomatidae), Stunkardiella minima (Stunkard, 1938), Alrophecaecum (?) astorquii (Watson, 1976), Peiaezia loossi (Pérez Vigueras, 1957) (Acanthostomidae); Ascocotyle (Ascocotyle) tenuicollis Price, 1935, Ascocotyle (Ascolotyle) sp. 1, Ascocotyle (Phagicola) diminuta (Stunkard et Haviland, 1924), Ascocotyle (Phagicola) sp. 2 (= Phagicola angrense Travassos, 1916 of Salgado-Maldonado and Aguirre-Macedo, 1991), Ascocotyle (Phagicola) sp. 3 (Heterophyidae); Cladocystis trifolium (Braun, 1901) (Opisthorchiidae); Oligogonotylus manieri Watson, 1976 (Cryptogonimidae); Clinostomum cf. complanatum (Rudolphi, 1814) (Clinostomidae); Diplostomum (Auslrodiplostomum) com-paclum (Lutz, 1928), Posthodiplostomum minimum (MacCallum, 1921), Posthodiplostomum sp. (Diplostomidae); Neodiplos-tomidae gen. sp. 1 ; Neodiplostomidae gen. sp. 2 (Neodiplostomidae); and Apharyngostrigea sp. (Strigeidae). All species found are described and figured, and their life cycles are briefly discussed.