Question

Planaria belongs to the phylum
a. Nemathelminthes
b. Platyhelminthes
c. Arthropoda
d. Mollusca

Answer 1

The organisms of phylum Platyhelminthes are also known as flatworms. Their bodies are compressed dorsoventrally, and show bilateral symmetry. The phylum includes many free-living and parasitic life forms.

Complete answer:
Planaria are free-living flatworms that live in freshwater bodies. They are characterized by a soft, broad, leaf-shaped body with cilia and a three-branched digestive tract. Like all other flatworms, Planaria belongs to the Kingdom Animalia, and the Phylum Platyhelminthes.

Among the given options:

Nemathelminthes are commonly called roundworms. It is a phylum of unsegmented, triploblastic, pseudocoelomate, cylindrical worms which are covered by a body wall with cuticle and epidermis.

Arthropoda is a phylum of animals with segmented body and jointed appendages. It includes many familiar forms like insects, lobsters, crabs, spiders, mites, millipedes and centipedes.

Mollusca is a phylum of soft-bodied, bilaterally symmetrical, segmented, coelomate animals. They usually have a mantle, ventral foot, anterior head, and a dorsal visceral mass.

So, the correct answer is B.

Additional Information:
Planaria is a common organism used for scientific research and classroom teaching. It has a great power of regeneration and it reproduces asexually which adds to research interest in it. As Planaria is probably the best known of the free-living platyhelminthes, it is largely used in intensive research related to cellular regeneration and pattern formation.

Note:
The Phylum Platyhelminthes (flatworms) includes tapeworms (Class Cestoda), flukes (Class Trematoda) and planarians (Class Turbellaria). Among them, the planarians are harmless, free-living flatworms. They live in an aquatic environment or on moist soil. Both tapeworms and flukes live as internal parasites that inhabit a host’s tissues.