Definition of miracidium in US English:



  • A free-swimming ciliated larval stage in which a parasitic fluke passes from the egg to its first host, typically a snail.

    • ‘Larval stages of some medically important species include miracidium, redia, cercaria, and metacercaria.’
    • ‘Whereas SmHox8, SmHox1, and Smox1 were all strongly expressed in eggs and miracidia compared to other stages, SmHox1 was much more weakly expressed in all the other stages.’
    • ‘By following this pathway, miracidia are immediately ready to infect other snails, thus by-passing two hosts in the parasite's life cycle, and creating the opportunity for direct, snail-to-snail transmission.’
    • ‘Not only do P. sinitsini become adults in E. symmetrica, but eggs are produced and hatch inside the daughter sporocysts, releasing free-swimming miracidia.’
    • ‘Generally, host seeking by miracidia includes a complicated behavioral process that is initiated through a combination of light and gravity stimuli.’


Late 19th century: from Greek meirakidion, diminutive of meirakion ‘boy, stripling’.