Definition: The term "Acanthocephali" refers to a group of parasitic worms that resemble spines, known as "acanthocysts", on their host's body. They are found in diverse ecosystems and are important prey for fish species. 1. Acanthocephaliaceae: These are the most common group in this taxon. 2. Acanthocephaloidea: The term includes all the other subfamilies that have similar characteristics. Examples include the Acanthocephalans (Acanthocephaloidea), which resemble spines, and the Acanthocephalids (Acanthocephaloidea).