Life cycles

Adult acanthocephalans are always intestinal parasites of vertebrates. Eggs pass in the feces of the host and must be eaten by an arthropod intermediate host. Within the arthropod, an acanthor hatches from the egg and penetrates the gut wall and enter the haemocoele. There it develops into an acanthella, in which the body wall and rudiments of the internal organs begin to take form. The final larval stage is the cystacanth, which possesses the proboscis of the adult form. The proboscis is retracted and a cyst wall forms around the parasite. At this stage, development ceases until the intermediate host containing a cystacanth is eaten be a definitive host. Then, the cyst ruptures, the parasite is freed, and the proboscis everts and attaches to the intestine.

Acanthocephalans may have aquatic or terrestrial life cycles. Many acanthocephalans are known to modify the behavior of their intermediate hosts to enhance the probability that those hosts are eaten by an appropriate definitive host.

A common feature of acanthocephalan life cycles is the use of paratenic hosts. If eaten by an unsuitable vertebrate host, the parasite may re-encyst until eaten by a suitable definitive host.