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the first larva in the development of trematodes, parasitic flatworms. The elongated body is 0.03 to 0.3 mm long and clad in large ciliated cells, which are usually distributed in four to six longitudinal rows. At the anterior of the body open the penetrative glands (a vestige of the intestine that has changed its primary function), whose secretions facilitate implantation of the miracidium in the body of the intermediate host. The organism’s nervous system is represented by the anterior medullary mass of nerve cells. The miracidia of many species have an X-shaped pigmented ocellus in front. The excretory organs are a pair of protonephridia. The body cavity contains germ cells. Miracidia usually emerge from the egg in water, swim for a time, and then implant themselves in the body of an intermediate host (usually a mollusk), where they are transformed into sporocysts.