Ribeiroia

Ribeiroia is a genus of parasite in the class Trematoda, phylum Platyhelminthes. Three species of Ribeiroia are currently recognized: R. ondatrae in the Americas, R. marini in the Caribbean, and R. congolensis in Africa.

The adult form lives in the intestines of greater than 40 species of birds and at least several species of mammals. Its eggs pass out in its host's faeces, and hatch into miracidia if the faeces falls into water.

The miracidium swims about until it finds a freshwater snail of the family Planorbidae. In the snail the miracidium develops into a redia which produces cercariae. The cercariae exit from the snail and penetrate the developing limb buds of a metamorphosing frog tadpole, usually the hind limb buds, and encyst there as metacercariae. As a result the affected limbs can develop wrongly, leading to various malformations such as extra limbs, missing limbs, skin webbings, and bony triangles.

In laboratory experiments, Ribeiroia also causes elevated mortality (up to 60%) in developing amphibian larvae. Malformed frogs may survive and mature, but the deformity makes the frog slower, and more easily caught by the parasite's definitive host (birds or mammals), whose gut digests the frog, releasing the parasite, which grows to adulthood in the predator's gut.