Infections by trematodes are among the most common fish-borne zoonoses. Metacercariae
of the Family Heterophyidae in marine and freshwater fishes are nonfastidious in their choice
of definitive hosts, and therefore, cause infections in human and domestic animals. In the present
study, species-specific polymerase chain reaction (PCR) assays were developed for identifying and
differentiating the various species examined. Sequencing and aligning the 18S (SSU) rDNA revealed
interspecific variation for which species-specific DNA oligonucleotides were designed and used for
the identification of 6 heterophyid species recovered from piscivorous birds. The oligonucleotides
were further used to evaluate the various stages (cercariae recovered from snails, metacercariae
recovered from fish and adult trematodes) of the digeneans. By applying this method we elucidated
for the first time the life cycle of Pygidiopsis genata. The phylogenetic interrelationship among the
newly sequenced species of Heterophyidae is outlined.