Diplostomida

Diplostomida is a suborder of the class Trematoda (flukes) within the phylum Platyhelminthes. Members of this group are digenean trematodes that parasitize aquatic vertebrates and have complex, indirect life cycles typically involving multiple hosts.

In the common Diplostomida cycle, eggs released with feces hatch into free-swimming miracidia that infect a snail, the first intermediate host. Inside the snail they develop to sporocysts or rediae, which produce cercariae that leave the snail and infect a second intermediate host, usually a fish, where they encyst as metacercariae in tissues such as the eye or gills. The parasite reaches maturity when a bird or other piscivorous vertebrate consumes the infected fish, completing the life cycle in the definitive host.

Diplostomids are well known for causing diplostomiasis in freshwater fish, particularly eye flukes that inhabit the lenses and ocular tissues. Infected fish may suffer reduced vision, impaired feeding, and higher mortality under some conditions. The parasites affect aquaculture and wild fish populations and can influence predator–prey interactions.

Taxonomy within Trematoda has undergone revisions; Diplostomida is recognized in many classifications as a suborder, but ranks and groupings can vary with different systems, especially as molecular data reshape relationships among digeneans.

Representative genera include Diplostomum, whose species such as Diplostomum spathaceum and Diplostomum pseudospathaceum are common eye flukes in freshwater fish.