Larval stages of trematodes from freshwater molluscs of the Yucatan Peninsula, Mexico

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: Echinochosmus leopoldinae Scholz, Ditrich et Vargas-Vazquez, 1996, E. macrocaudatus Ditrich, Scholz et Vargas-Vazquez, 1996 (Echinostomatidae), Saccocoelioides sp. (? sogandaresi Lumsden, 1963) (Haploporidae), Crassicutis cichlasomae Manter, 1936, pleurolophocercous ophthalmocercaria sp. (Homalometridae), Ascocotyle (Ascocotyle) sp., Ascocotyle (Phagicola) nana Ransom, 1920 (Heterophyidae), Oligogonatylus manteri 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 caronatus (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 Sukez-Morales, 1996), into metacercariae resembling by their morphology juvenile trematodes found in the stomach of Astya 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.