Which phylum do roundworms belong in

The overall morphology of these worms is cylindrical, as seen in Figure 1. The head is radially symmetrical. A mouth opening is present at the anterior end with three or six lips as well as teeth in some species in the form of cuticle extensions. Some nematodes may present other external modifications like rings, head shields, or warts. Rings, however, do not reflect true internal body segmentation. The mouth leads to a muscular pharynx and intestine, which leads to a rectum and anal opening at the posterior end.

The muscles of nematodes differ from those of most animals: They have a longitudinal layer only, which accounts for the whip-like motion of their movement. Figure 1. Scanning electron micrograph shows a the soybean cyst nematode Heterodera glycines and a nematode egg. In nematodes, specialized excretory systems are not well developed. Nitrogenous wastes may be lost by diffusion through the entire body or into the pseudocoelom body cavity , where they are removed by specialized cells.

Also known as the human whipworm, Trichuris trichula are roundworms that are responsible for trichuriasis. Some of the other worms affect other types of animals. For instance, Trichinella spp. As well, some members of Dioctophyme can affect both human beings and various carnivores and survive as parasites.

Enoplia - This subclass is characterized by oval or pouch-like amphids, cylindrical esophagus, and smooth body. It includes the members of Orders Trefusiida and Enoplida. Dorylaimia - Members of this sub-class can be found in different terrestrial and freshwater environments. A majority of these species are free-living organisms that either exist as predators or omnivorous in their respective environments. However, some, like Trichinellida live as parasites. Chromadorea, a class of Nematoda only consists of a single subclass Chromadoria which in turn consists of several orders.

Members of this class are characterized by three esophageal glands, spiral amphids as well as having annules. The amphid of Chromadorea are pore-like and may range from labial to post-labial coil or spiral-like apertures. Compared to members of Enoplea, Chromadorea possess annulated cuticles that may be decollated with projections and setae. If present, phasmids are located at the posterior end while their excretory systems may either be glandular of tubular in appearance.

Compared to Anoplia, Chromadoria is currently said to consist of about four distinct lineages. As a result, this class of nematodes can be found in a wider range of habitats. For instance, while some species can be found in marine environments, others can be found in various terrestrial habitats including on such plants as mosses and lichens to different types of soils.

Their cuticle has also been shown to have gone through significant evolutionary modifications, which may help explain their ability to live and survive in different habitats as well as ornamentations. Among members of the order Rhabditida, researchers discovered a chemically impermeable cuticle which enables the worms to survive in various extreme habitats and also thrive as parasites. Apart from the cuticle, modifications identified in the pharynx of these worms have also been attributed to evolutional developments.

This has allowed these organisms to develop a more compact body design when compared to members of class Enoplia. This class is also composed of both free-living and parasitic members.

As compared to Enoplia and Dorylaimia worms, free-living Chromadorea are smaller in size. However, they also reproduce at a higher rate and are therefore greater in number in their habitats. For some of the species, compressed generation time has been shown to play an important role in their ability to effectively colonize their habitats. Apart from this evolutionary advantage, they have also been shown to have other adaptations that enhance rapid dispersal to other habitats.

The eggs hatch into larvae, which develop into adults. Then the cycle repeats. Roundworms may be free-living or parasitic. Free-living worms are found mainly in freshwater habitats. Some live in soil.

They generally feed on bacteria, fungi, protozoans, or decaying organic matter. By breaking down organic matter, they play an important role in the carbon cycle. Parasitic roundworms may have plant, vertebrate, or invertebrate hosts. Several species have human hosts. For example, hookworms, like the one in Figure below , are human parasites. They infect the human intestine.

Hookworm larvae enter the host through the skin. They migrate to the intestine, where they mature into adults. Adults lay eggs, which pass out of the host in feces.

Most flatworms can reproduce sexually or asexually. Rotifer features and movement Rotifers are similar to round worms because they have bilateral symmetry and are pseudocoelomates with a gut open at both ends. Unlike round- worms, rotifers move through the water by means of their cili- ated wheel-like structures, which are shown in Figure The pseudocoelom contains the coelomocytes see Coelomocyte Section , provides the turgor-hydrostatic pressure for the animal as a whole, functions as a lubricant between tissues, and provides a medium for intercellular signaling and nutrient transport.

Roundworms reproduce sexually. Sperm and eggs are produced by separate male and female adults. Fertilization takes place inside the female organism. The eggs hatch into larvae, which develop into adults. Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and forth.

No cilia or flagellae are present. Symptoms: No symptoms to very mild symptoms. Moderate infections may cause burning in the abdomen, nausea, vomiting, and alternating diarrhea and constipation. Severe infections include anemia, weight loss, and chronic diarrhea. Worms vomited up or visible in stools. Needless to say, it can be quite alarming and disgusting to see these large, pale-colored, spaghetti-like worms—sometimes still moving.

Another way is their complete digestive system. It allows them to take in food, digest food, and eliminate wastes all at the same time. Roundworms have a tough covering of cuticle on the surface of their body.

It prevents their body from expanding. A flatworm has a thin, dorsoventrally flattened body. Roundworms are more cylindrical in shape and tapered to a fine point at one end. Flatworms generally live in bodies of water, while roundworm species can live either on water or in soil. Ascariasis is an infection of the small intestine caused by Ascaris lumbricoides, which is a species of roundworm. Roundworms are a type of parasitic worm. Infections caused by roundworms are fairly common.

Ascariasis is the most common roundworm infection.