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(invertebrate zoology)
The ciliated first larva of a digenetic trematode; forms a sporocyst after penetrating intermediate host tissues.



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.

References in periodicals archive ?
Hence, we expect that the final definition of risk groups will be based on both infection data and spatial features, the latter related to the clear importance of surface water transport of cercaria and miracidia.
k] Spatial index for the 1 (default value) distribution and interaction between snails and miracidia Inputs p Rainfall (mm/day) Local data [T.
alternata can function as the primary intermediate host for the miracidia (Jenson 1972).
Miracidia are motile and remain infective for 8-12 hours, locating the intermediate snail host by chemotactic stimuli.
This process normally takes up to four weeks producing an intermediate stage called miracidia which must infect a particular type of snail within three hours.
These receptors (SSTRs), presence of whom have been confirmed in humans, rats and mice, have now been shown by us also on the miracidia, worm tegument and internal structures of S.
Feces from infected individuals contaminate the local water with eggs, and the eggs release motile miracidia that in turn infect freshwater snails.
Sperm and ovaries, as well as ova with developing miracidia within them, were present in several trematodes.
The miracidia mature inside the snails to become cercariae, which are released back into the water, and can penetrate the water-softened skin of unsuspecting humans.