Miracidium

Miracidium

A miracidium is a small free-living larval stage of parasitic flatworms in the class Trematoda. It is released from eggs which are usually shed in the faeces of its vertebrate host. When an egg is immersed in water, its operculum liberates the miracidium, which swims using cilia to find the first host in its life cycle, a mollusc. Miracidia are transmission stages that do not feed and, if they do not find a molluscan host, do not survive much beyond 24 hours. It goes through various stages in its mollusc host; the details vary with species:-
*Miracidium: settles in the mollusc and becomes a sporocyst.
*Sporocyst: produces either more sporocysts, or rediae.
*Redia: produces either more rediae, or cercariae.:In some species the redia stage is missed out, and sporocysts produce cercariae.
*Cercaria: This is somewhat like a small adult, but has a large swimming tail somewhat like a tadpole's (but without a notochord or backbone, as it is not a chordate). It finds and settles in a host, and becomes an adult, or a mesocercaria, or a metacercaria, according to species.
*Mesocercaria: A cercaria little modified but resting.
*Metacercaria: A cercaria encysted and resting.
*Adult.

With some species of Trematoda the cercaria develops into an adult in that host.

With other species of Trematoda (for example Ribeiroia) the cercaria encysts, and waits until the host is eaten by a third host, in whose gut it emerges and develops into an adult.

In its final host, it eventually lays eggs which are discharged in its host's faeces. From there the eggs hatch in the presence of free water and the miracidium stage of life is reached again.

External links

*A set of pages:-
**http://www.path.cam.ac.uk/~schisto/OtherFlukes/Flukes_Gen/Fluke_Life1.html
**http://www.path.cam.ac.uk/~schisto/OtherFlukes/Flukes_Gen/Fluke_Life2.html
**http://www.path.cam.ac.uk/~schisto/OtherFlukes/Flukes_Gen/Fluke_Life3.html
**http://www.path.cam.ac.uk/~schisto/OtherFlukes/Flukes_Gen/Fluke_Life4.html
**http://www.path.cam.ac.uk/~schisto/OtherFlukes/Flukes_Gen/Fluke_Life5.html


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  • Miracidium — Als Miracidium oder Wimpernlarve bezeichnet man ein Lebensstadium der parasitischen Saugwürmer (Trematoda) und Hakensaugwürmer (Monogenea), bei letzteren wird es allerdings meist als Oncomiracidium bezeichnet. Beispiele für Arten sind etwa die… …   Deutsch Wikipedia

  • Miracidium —   [von griechisch meirakídion »Knabe«, »Bürschchen«] das, s/...di |en, birnenförmige, bewimperte, erste Larvenform bei Saugwürmern; sie ist entweder frei schwimmend oder schlüpft bei landbewohnenden Zwischenwirten erst nach der Aufnahme des Eies… …   Universal-Lexikon

  • miracidium — MIRACÍDIUM s.m. Larvă a distomului, ciliată, având înfăţişarea unor infuzori. [pron. di um. / et. incertă]. Trimis de LauraGellner, 13.09.2007. Sursa: DN  MIRACÍDIUM s. m. larvă a distomului, ciliată, având înfăţişarea unor infuzori. Trimis de… …   Dicționar Român

  • Miracidĭum — Miracidĭum, die bewimperte Larve der Saugwürmer, s. Plattwürmer …   Meyers Großes Konversations-Lexikon

  • miracidium — ● miracidium nom masculin Première larve, microscopique, des vers trématodes, qui s installe dans le poumon d un gastropode dulcicole (limnée, planorbe) et se transforme en sporocyste …   Encyclopédie Universelle

  • miracidium — noun (plural miracidia) Etymology: New Latin, from Greek meirak , meirax youth, stripling + New Latin idium Date: 1898 the free swimming ciliated first larva of a digenetic trematode that seeks out and penetrates a suitable snail intermediate… …   New Collegiate Dictionary

  • miracidium — n.; pl. dia [Gr. dim. meirakion, young girl] (PLATYHELMINTHES: Trematoda) In Digenea, the first larval stage; a ciliated, free swimming form …   Dictionary of invertebrate zoology

  • miracidium — miracidial, adj. /muy reuh sid ee euhm/, n., pl. miracidia / sid ee euh/. the larva that hatches from the egg of a trematode worm or fluke. [1895 1900; < NL, equiv. to mirac ( < Gk meirak (s. of meîrax) boy, girl) + idium IDIUM] * * * …   Universalium

  • miracidium — The ciliated first stage larva of a trematode that emerges from the egg and must penetrate into the tissues of an appropriate intermediate host snail if it is to continue its life cycle; followed by development into a mother …   Medical dictionary

  • miracidium — n. larva that hatches from the egg of a worm …   English contemporary dictionary

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