The fossil of Juracanthocephalus daohugouensis from the Daohugou biota reveals the evolution of thorny-headed worms

演化之聲
Mar 14
4 min read

Acanthocephalans are a group of obligate parasitic animals, with nearly 1,500 species currently known. Their life cycles are complex and usually involve two or more hosts. During the larval stage they parasitize invertebrate hosts such as crustaceans and insects, whereas the adult stage occurs in vertebrate hosts including fishes, birds and mammals. Because they are obligate parasites, acanthocephalans lack a mouth and digestive tract. Adult individuals live in the digestive tract of the final host and absorb nutrients directly from the host's intestine through their body surface. The most distinctive structure of acanthocephalans is the proboscis at the anterior end of the body. This organ is covered with multiple rings of hooks arranged in circular rows. These hooks pierce and anchor into the intestinal wall of the final host, allowing the parasite to remain firmly attached and preventing it from being dislodged by intestinal movements. The proboscis can be everted outward from the body, and when attachment is not required it can be withdrawn by muscular contraction into an internal proboscis receptacle.