The Roundworm's Digestive System

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Roundworms are a type of nematode with a relatively simple digestive system. In this lesson, we will take a more detailed look at roundworm digestion and see how it contrasts to other groups of worms.

What is a Roundworm?

Roundworms are found within the phylum Nematoda. They are a group of worms more advanced than flatworms, but less advanced than earthworms (roundworms are not segmented like earthworms). A number of parasites, including hookworms, pinworms, and Trichinella are classified as different types of roundworms. In fact, more than 15,000 species of roundworms have been identified thus far.

Like other types of worms, roundworms live either in an aquatic environment or in the soil. It's necessary for them to stay wet or moist at all times. Non-parasitic roundworms will often live in the substrate of a body of water and they are free swimming, meaning they can venture about to find food. Parasitic roundworms get their nutrition from a host and can live either attached to the body, or even inside it. For example, parasitic species of roundworms like Ascaris live in the intestines of humans and can grow to a foot in length. Additionally, like other worms, they have an elongated, narrow cylindrical body that varies in size.

An adult parasitic roundworm

Roundworm Digestion

The roundworms represent a pretty magnificent leap in terms of how their digestive system is structured. Unlike their predecessors, roundworms have a tube digestive system, meaning food flows in one direction (in one end and out the other). This is in contrast to the digestive system of the flatworms: these organisms have a single opening. Food enters into a sac, digestion takes place, and waste is eliminated through the same opening. Once food enters a roundworm, it is pushed down the tube through a series of muscle contractions.

Let's take a closer look. A roundworm eats food that enters its mouth. The mouth signals the starting point of the digestive system. The food itself is consumed when the surrounding muscles (called pharyngeal muscles) contract, creating a vacuum-like suction. Some roundworms have a structure that they use to pierce food, either to suck out juices or to stab the item to ingest it. Once the food is in the mouth, it moves down to the pharynx (or throat). The pharynx is where food is crushed down before it continues into the long gut, or intestine.

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