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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 ?
Comparative gene analysis of Biomphalaria glabrata hemocytes pre- and post-exposure to miracidia of Schistosoma mansoni.
Oligochaetes may protect some snails from trematode infections by ingesting miracidia or by limiting the parasites' access to the mantle cavity (Ibrahim 2007).
Miracidia found were confirmed as Szidatitrema species, consistent with the trematode identified in the index cases and by fecal monitoring of the collection.
To develop further the egg must reach tepid (22[degrees]C to 26[degrees]C) surface water, where miracidia (larvae) develop and hatch within approximately 1 to 2 weeks.
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.
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.
Because the lifetime of both cercaria and miracidia is less than a day, and the time step of the model for simulation purposes is 1 day, these relationships are algebraic.
In experimental studies of other snail-trematode systems, if miracidia (searching stages hatched from trematode eggs) were selective, they were more likely to penetrate snails infected with other trematode species than uninfected snails (Heyneman et al.
We performed molecular analysis of schistosomal miracidia DNA.