Notes

Based on a study by Natalia Ershova published in 2019 about Trematodes in intertidal communities

The typical digenean trematode life cycle has adult worms living in the digestive system of the definitive host. Adults release eggs, which upon entering the environment must hatch into miracidia larvae (Figure 1). The miracidia then find a suitable first intermediate host, which is almost always a mollusk. The trematode then reproduces asexually in the first intermediate host and produces a free-living ceraciae larvae which must find a suitable second intermediate host and form a metacercariae in its body tissues. The metacercariae is than ingested with the second intermediate host by a primary host, completing the life cycle

4 Figure 1. The life-cycle of a typical trematode (from Sukhdeo 2012). In marine systems, we are learning a lot about trematodes due to the accessibility of their first intermediate hosts. Intertidal snails serve as first intermediate hosts for dozens of trematode species, they are easily collected in large numbers, are easy to keep in the lab, and the infection status of the snail can be identified both while the snail is alive and post mortem. Additionally, many intertidal invertebrate species act as a second intermediate hosts for trematodes (mussels, amphipods, crabs, barnacles, annelids and so on). For most marine trematode species shore birds are the final hosts.