The life cycle of Zygocotyle lunata (Trematoda, Paramphistomoidea) in the subtropical region of South America

The life cycle of the trematode Zygocotyle lunata (Diesing, 1836) is studied, beginning with cercariae from naturally infected Biomphalaria peregrina (d’Orbigny, 1835) and B. tenagophila (d’Orbigny, 1835) from Buenos Aires Province and Salta Province (Argentina), respectively. Adults were recovered from Gallus domesticus (Linnaeus, 1758) and Mus musculus (Linnaeus, 1758). Egg development lasted for 15-23 days at 23-24 C, and 10-12 days at 28-30 C; it was delayed after successive passages through mice, and ceased thereafter. In the snail, sporocysts, located beneath the mantle border, occurred up to 37 days post exposure (PE). Rediae invaded the entire snail body; developing cercarial bodies within rediae were recognized by the presence of a short tail, excretory canals, and eye-spot pigment. Cercariae emerged from snails as early as 20-26 days PE, encysting immediately on any substrate. These can be easily differentiated from those of Paramphistomum Fischoeder, 1901 spp. and Cotylophoron Stiles and Goldberger, 1910 spp., which have lateral excretory tubes forming a ring at the midlevel of the body and usually lack pharyngeal appendages. Metacercariae were infective for at least 6 months. Mature adults were observed 27-32 days PE in mice and 35 days PE in chicks. Biomphalaria tenagophila represents a new intermediate natural host record and Salta Province a new geographic area; Den