Question

Ascaris belongs to
A. Cestoda
B. Nematoda
C. Trematoda
D. Turbellaria

Answer 1

The species of Ascaris are very large. The length of an adult female is about 20 to 35 cm and that of an adult male is about 15 to 30 cm. Ascaris parasitize inside the human intestine. The species of Ascaris i.e. Ascaris lumbricoides affects humans and is responsible for causing ascariasis in humans. So, Ascaris is also known as small intestinal roundworms.

Complete answer:
Cestoda belongs to the phylum Platyhelminthes. It belongs to the class of parasitic worms and of the subclass Eucestoda. Cestoda are ribbon-like worms and are referred to as tapeworms. Many identical units known as proglottids are present all over the body. Nematodes belong to the phylum of invertebrates. These are abundantly present on earth. They are bilaterally symmetrical. The body plan of nematodes is simple. The genus of the parasitic nematode is Ascaris. Trematoda falls under the class of the phylum Platyhelminthes. They are known as Flukes. There are approximately 176 different families under Trematoda. These worms are about 1mm to 7 m long, but usually are 0.5-5 cm. Turbellaria belongs to phylum Platyhelminthes and comprises all the sub-groups which are not entirely parasitic. It is distinguished by the presence of soft epidermis i.e. ciliated, at least on the ventral surface.

So, the correct answer is Option B i.e. Nematode.

Note:
There about 6,000 species of class Trematoda exist, although the number of species varies, among various experimenters. Nematodes are worm-like organisms that are enclosed by a powerful, adjustable noncellular membrane known as the cuticle. This cuticle covers a layer of epidermal cells.