Clinostomum marginatum is a yellow flatworm that can grow up to 6.4 millimetres (0.25 in) in the flesh of freshwater fish or the muscle of frogs.

Distinguishing characteristics of this parasite in the "miracidium" stage are three eyespots located on the mid-dorsal line, posterior of lateral papillae.

However, specimens found in herons were smooth, had thick teguments, and absorbed food (such as glucose) through facilitated diffusion.

The cercariae form exits the snail and is free swimming in water, in search for a fitting fish host.

They burrow inside the fish or frog host, and the cercariae encyst and continue its next larval stage, known as "metacercariae", which are the yellow grubs.

The eggs of the parasite known as a metacercariae are then released into the water through the bird's mouth when feeding and become adult flukes.

These parasites may feed on the mucus of organs, food content ingested by the host, blood and tissue from eroding epithelial surfaces.