Gyrodactylidea

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Gyrodactylidea are an order of parasitic flatworms that live on fish. They belong to the phylum Platyhelminthes, class Monogenea, and subclass Monopisthocotylea. Members attach to fish using a specialized organ called a haptor.

Families in this order include: Acanthocotylidae, Anoplodiscidae, Bothitrematidae, Gyrodactylidae, Tetraonchoididae, and Udonellidae.

An example is Gyrodactylus alexanderi, a parasite found on the three-spined stickleback (Gasterosteus aculeatus).