Dominic Stone
Roundworms, or nematodes, are among the most ubiquitous organisms on Earth. They live in almost every geographic location, including extreme habitats like ice and hot springs. With over 80,000 known species, they are one of the most diverse animal phyla. Roundworms have a complete digestive system, a tough outer cuticle, and a body plan that is more complex than flatworms. But do roundworms have muscles?
| Characteristics | Values |
|---|---|
| Roundworm body shape | Round |
| Roundworm phylum | Nematoda |
| Number of known species | 80,000+ |
| Length | 1mm-7m |
| Roundworm covering | Cuticle |
| Roundworm movement | Longitudinal muscles |
| Roundworm digestive system | Complete |
| Roundworm nervous system | Dorsal and ventral nerve cords |
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What You'll Learn
Roundworms have longitudinal muscles
Roundworms, or nematodes, are a diverse phylum of worms with a round body cross-sectional shape. They are bilaterally symmetrical, worm-like organisms surrounded by a strong, flexible noncellular layer called a cuticle. This cuticle is the closest thing a roundworm has to a skeleton, and it is used as a support and leverage point for movement.
The contraction of the longitudinal muscles on either side of the roundworm's body creates a characteristic thrashing movement as the worm wriggles forward. This is distinct from the crawling movement of other worms, which is produced by the contraction of circular muscles that roundworms lack. The cuticle, or outer covering, of roundworms also plays a role in their movement by preventing swelling. This ensures that the contraction of one muscle group stretches the other, creating antagonistic forces between the dorsal and ventral longitudinal muscles.
Roundworms are either free-living or parasitic. Free-living nematodes are abundant in soils and sediments, where they feed on bacteria and detritus, while parasitic nematodes can infect both plants and animals, including humans.
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They use their cuticle for support and leverage
Roundworms, or nematodes, have a cuticle on the surface of their bodies. This cuticle acts as a form of support and leverage for the worm, as it is the closest thing a roundworm has to a skeleton. The cuticle is periodically shed during the life of a nematode as it grows, usually four times before it reaches the adult stage.
The cuticle is a waxy covering secreted by the epidermis, or outermost cellular tissue. It is a very complex feature with important functions involving protection, body movement, and maintaining shape. The cuticle is thick and allows bending but prevents swelling, ensuring that the contraction of the longitudinal muscle can only bend the body. This means that roundworms do not bend from side to side like eels or snakes, but up or down (dorsally or ventrally).
The prevention of swelling by the cuticle makes the dorsal and ventral longitudinal muscles antagonistic to one another. This means that the shortening of one muscle group causes the other to stretch. The muscles of roundworms are all aligned longitudinally along the inside of the body, and they are activated by two nerves that run the length of the nematode on both the dorsal (back) and ventral (belly) sides.
The cuticle also has a protective function, as it prevents the body of the roundworm from expanding. This allows for the buildup of fluid pressure in the pseudocoelom, which is a fluid-filled cavity between the body wall and the gut. This fluid supports the soft tissues of the body wall.
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Their muscles are activated by nerves
Roundworms, or nematodes, have a body cavity and a complete digestive system. They have a mouth at one end, a long tube with specialised parts in the middle, and an anus at the other end. They have a tough covering of cuticle on the surface of their body, which is periodically shed as the worm grows. This cuticle is the closest thing a roundworm has to a skeleton, and the worm uses it as a support and leverage point for movement.
Roundworms have muscles, but they are different from those of other worms. While most worms have two bands of muscles, roundworms only have longitudinal muscles. These muscles lie just underneath the epidermis and are aligned longitudinally along the inside of the body. This means that roundworms can only bend their bodies up or down (dorsal or ventral), rather than from side to side.
Unlike other animals, where the nerves branch out to the muscle cells, a roundworm's muscle cells branch towards the nerves. This unique feature of roundworms highlights the complex nature of their muscular and nervous systems.
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They lack circular muscles
Roundworms, or nematodes, are among the most ubiquitous organisms on Earth. They are found in almost every geographic location, including extreme habitats like ice and hot springs, and they can live in or on almost every type of plant and animal, including humans.
Roundworms have a round body cross-sectional shape, and they have a complete digestive system, with a mouth at one end and an anus at the other. They also have a tough covering of cuticle on the surface of their body, which acts as a support and leverage point for movement.
While most worms have two bands of muscles—longitudinal muscles that run the length of the body and circular muscles that form circular bands around the body—nematodes only have longitudinal muscles. This means they cannot crawl or lift themselves and instead move by contracting the long muscles on either side of their body, resulting in a thrashing or wriggling movement.
The lack of circular muscles in roundworms means that they can only bend their bodies up or down (dorsal or ventral) rather than from side to side like eels or snakes. This is because the cuticle covering prevents swelling, so the contraction of the longitudinal muscles can only result in bending the body in one direction.
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They have radial muscles in the pharynx
Roundworms, or nematodes, have a round body cross-sectional shape and are part of the phylum Nematoda. They have a complete digestive system, with a mouth at one end and an anus at the other. Unlike other worms, roundworms only have longitudinal muscles. These muscles are all aligned longitudinally along the inside of the body, allowing the nematode to bend its body from side to side, rather than crawl or lift itself.
Roundworms have a tough covering of cuticle on the surface of their body, which is periodically shed as the worm grows. The cuticle acts as a support and leverage point for movement, and the muscles underneath allow the roundworm to move by contracting.
Roundworms have radial muscles in the pharynx, which is encircled by a nerve ring called the circumpharyngeal commissure. The pharynx is lined with cuticle and externally by a membrane (basal lamella). It contains radial muscles, oesophageal glands, and valves, which prevent the regurgitation of food. In some nematodes, the median and posterior parts of the pharynx are swollen to form muscular bulbs.
The nervous system of roundworms is comprised of anterior nervous tissue surrounding the pharynx, which forms dorsal and ventral nerve cords that run from end to end. The nerve ring, or circumpharyngeal commissure, is part of the central nervous system, which also includes interneurones, connected ganglia, and the ventral nerve bundle.
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Frequently asked questions
Yes, roundworms have muscles. They have longitudinal muscles that run the length of their bodies. These muscles are activated by two nerves that run the length of the nematode on both the dorsal (back) and ventral (belly) sides.
Roundworms can only move by contracting their longitudinal muscles, which makes them thrash and wriggle rather than crawl.
The muscles surrounding the digestive tube contract, squeezing the food and pushing it along in a process called peristalsis.
