diplostomid

Diplostomids are a family of digenean trematodes, commonly known as fork-tailed flukes. These parasites are found in a wide range of vertebrate hosts, including fish, amphibians, reptiles, birds, and mammals. The life cycle of diplostomids is complex, typically involving three hosts: a mollusk as the first intermediate host, a vertebrate as the second intermediate host, and a predatory vertebrate as the definitive host.

The first larval stage, the miracidium, hatches from eggs in the water and infects a suitable mollusk. Within the mollusk, it develops into a sporocyst and then into cercariae. The cercariae are released from the mollusk and actively seek out a second intermediate host, usually a fish. They penetrate the fish's skin or gills and encyst in various tissues, most commonly in the lens of the eye, forming metacercariae.

When the infected fish is eaten by a definitive host, the metacercariae excyst in the digestive tract and migrate to their final location, often the intestine or blood vessels. Adult flukes reproduce sexually, and eggs are shed in the feces of the definitive host, completing the cycle. Diplostomid infections can have significant impacts on their hosts, particularly in fish where metacercariae in the eye can cause cataracts and impair vision, affecting foraging and predator avoidance. Some species are of veterinary or economic importance.