cystacanth

invertebrate

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Last updated

June 25, 2026

Quick Summary

A cystacanth is a dormant larval stage of spiny-headed worms, which are invertebrate animals belonging to the phylum Acanthocephala. These parasites are found worldwide and infect vertebrates as adults and arthropods as juveniles.1

The life cycle involves the fertilized eggs being excreted by the vertebrate host and then ingested by an arthropod intermediate host. Inside the arthropod, the larva develops into an acanthella and then a cystacanth. This cystacanth stage is a miniature version of the adult worm, with its proboscis withdrawn. The cystacanth remains infective until ingested by a definitive vertebrate host, where it matures. While typically infecting fish, spiny-headed worms can also parasitize amphibians, reptiles, birds, and mammals. Humans are rarely infected accidentally.1

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spiny-headed worm
Natural history.
…it is known as a cystacanth. Once again, no further development occurs unless the cystacanth is ingested by its definitive host, a vertebrate. If ingested, the young spiny-headed worm emerges inside the vertebrate’s intestine, uses its proboscis to bore into the gut wall, and matures there.
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…it is known as a cystacanth. Once again, no further development occurs unless the cystacanth is ingested by its definitive host, a vertebrate. If ingested, the young spiny-headed worm emerges inside the vertebrate’s intestine, uses its proboscis to bore into the gut wall, and matures there.
Read More