Question

Phylum Nemathelminths includes these very common organisms, some of which are parasitic and most of which are often found in soil. Which of the following is it?
A) Segmented worms
B) Flatworms
C) Earthworms
D) Roundworms

Answer 1

Hint: These organisms are of varied length having long round bodies. The presence of pseudocoelom is their characteristic feature.

Complete answer:
The organisms belonging to Phylum Nemathelminthes, that are very common organisms, and are parasitic and most of which are often found in soil are called roundworms.

Fig: Roundworms

Additional information:
The common name for Aschelminthes is roundworms because the body appears circular in the transverse cross-section. This circular appearance in a transverse plane gives the common name roundworm.
General characteristic features of Aschelminthes:
- Habit and Habitat: They may be free or parasitic Free-living roundworms do not live within other animals and are independent. They may be aquatic or terrestrial.
- These are triploblastic, pseudocoelomate, bilaterally symmetrical having an organ system level of organization.
- They have an elongated, cylindrical body that tapers towards both ends.
- The digestive system is complete, having two separate openings. Tube within tube body plan. The stomach is absent in parasitic forms. Extracellular digestion. The roundworms have well developed muscular pharynx.
- H shaped Renette cells are present for excretion.
- They lack a circulatory system.
- They have a poorly developed nervous system.
- Sexes are separate. Females are often larger than males.
- Both direct and indirect development is present.

So, the correct answer is ‘Roundworms’.

Note: Aschelminthes is a superphylum where all pseudocoelomates are placed. This phylum is represented by about 15,000 species of roundworms. Parasitic roundworms live in plants and animals called endoparasites.