Range: Worldwide Habitat: Inside host fosh, birds, reptiles, and mammals; Typically in the intestines Size: About 1 inch (2.54cm) long; Up to 3 feet (1m) long Diet: Host nutrients Threats: None Life span: Lifespan of the host

Transcript:

Today on Animal Fact Files we’re discussing acanthocephalans. These are endoparasites, meaning they spend almost their entire lives inside the body of another animal, also known as the host. In the case of these invertebrates, they specifically go through two hosts before they reach their adult stage. Acanthocephalans are also known as thorny headed or spiny headed worms and this is due to their spiny proboscis which is used to anchor them to the internal organs, usually the intestines, of a host.

There are over 1,000 described species of spiny headed worms and they are found all throughout the world. When they aren’t living inside a host, they live in fresh or marine water. In size, most adults barely reach an inch (2.54cm) in length, though the largest species may be nearly three feet (1m) long! They’re most prevalent in fish, but they have been found in every type of vertebrate animal including birds, reptiles, and mammals.

Spiny headed worms start out as eggs. These are laid by a female, who are larger than males, and shed in the host’s feces. Though some of the worms we’ve talked about on this show, like earthworms, are hermaphroditic, spiny headed worms have separate sexes and will appear with either male or female organs. The eggs must be eaten by the first host, also known as the intermediate host, in order to hatch and develop. Typically, the intermediate host for spiny headed worms are insects, like cockroaches, or crustaceans.

While in this host, the spiny headed worm undergoes three larval stages. This takes about two or three months. Once completed, and after the intermediate host has been eaten by the second and final host, the spiny headed worm will become sexually mature and begin breeding (again with this occurring after about two to three months inside the host). These endoparasites are considered rare in comparison to others such as tapeworms, however, there may be dozens of adults inside a single host’s body depending on the species. There was once a seal found with more than 1,000 adult acanthocephalans in its gut.

This might sound alarming, since these animals can infect humans, however, fewer than a dozen species have been identified in human populations, and they often end up in us by accident. Spiny headed worms may appear in the guts of people who live in communities where insects are frequently consumed or they may make their way in when children inadvertently eat insects. So I suppose there are some reasons it’s better for kids to learn about nature through the screen as opposed to first hand experience!

The body structure of these worms consists of the spiny proboscis which is usually used to determine the species, the neck, and the truck which makes up a large majority of the worm’s body. These invertebrates lack a digestive or respiratory tract and instead absorb nutrients from their host through their body wall. They may be able to survive in the host for as long as the host lives, especially in the case of intermediate hosts who first must be eaten for the parasite to fully develop.

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