roundworms

roundworms in the environment

Roundworms can be free-living organisms, but they are probably best known for their role as significant plant and animal parasites. Most Nematodes are parasitic, with over 16,000 parasitic species described. Heartworms, which cause serious disease in dogs while living in the heart and blood vessels, are a type of roundworm. Roundworms can also cause disease in humans. Elephantiasis, a disease characterized by the extreme swelling of the limbs ( Figure Most parasitic roundworm eggs or larvae are found in the soil and enter the human body when a person picks them up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly through the skin. The best solution to these diseases is to try to prevent these diseases rather than treat or cure them. Diseases caused by roundworms are more common in developing countries. Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include lack of a clean water supply, inadequate sanitation measures, crowded living conditions, combined with a lack of access to health care and low levels of education.

features of roundworms

  1. Unlike the flatworms, the roundworms have a body cavity with internal organs. 2. A roundworm has a complete digestive system, which includes both a mouth and an anus. This is a significant difference from the incomplete digestive system of flatworms. The roundworm digestive system also include a large digestive organ known as the gut. Digestive enzymes that start to break down food are produced here. There is no stomach, but there is an intestine which produces enzymes that help absorb nutrients. The last portion of the intestine forms a rectum, which expels waste through the anus. 3. Roundworms also have a simple nervous system with a primitive brain. There are four nerves that run the length of the body and are connected from the top to the bottom of the body. At the anterior end of the animal (the head region), the nerves branch from a circular ring which serves as the brain. The head of a nematode has a few tiny sense organs, including chemoreceptors, which sense chemicals. Though still a relatively simple structure, the nervous system of roundworms is very different from that of the cnidarian nerve net.

roundworms

The word "worm" is not very scientific. This informal term describes animals (usually invertebrates) that have long bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms ( Figure 1.1). They are classified in the phylum Nematoda, which has over 28,000 known species. Some scientists believe there could be over a million species of Nematodes. Nematodes are slender bilaterally symmetrical worms, typically less than 2.5 mm long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 cm, and some parasitic species are larger still, reaching over a meter in length. The worm body is often covered with ridges, rings, bristles, or other distinctive structures. The radially symmetrical head of a nematode also has distinct features. The head is covered with sensory bristles and, in many cases, solid "head-shields" around the mouth region. The mouth has either three or six lips arranged around the mouth opening, which often have a series of teeth on their inner edges. Nematodes can be parasites of plants and animals.

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instructional diagrams

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questions

some worms can have six lips.

-->  a. true

b. false

most nematodes are harmful.

-->  a. true

b. false

how many species of parasitic roundworms have been identified?

-->  a) about 1,600

b) about 1,6000

c) about 28,000

d) over 150,000

which best describes the nematode digestive system?

-->  a) a complete digestive system, with both a mouth and an anus.

b) a complete digestive system, with just a mouth.

c) an incomplete digestive system, with just a mouth.

d) an incomplete digestive system, with both a mouth and an anus.

which best describes the nematode brain?

a) a circular cluster of nervous tissue

b) a nerve net attaching at the head region

-->  c) a circular ring of nerves

d) none of the above describe the nematode brain.

how do roundworms get rid of waste?

a) through the one opening of the gastrovascular cavity.

-->  b) through the anus at the end of the digestive tract.

c) through the mouth, which serves to both ingest food and expel waste.

d) all of the above

factors contributing to parasitic roundworm diseases include

a) crowded living conditions.

b) inadequate sanitation measures.

c) lack of a clean water supply.

-->  d) all of the above

diagram questions

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