Question

Which is a free living freshwater flatworm?
A. Planaria
B. Fasciola
C. Taenia
D. Pheretima

Answer 1

Hint: Flatworms are the group of organisms that possess a soft body and are flattened invertebrates. A number of flatworm species are free-living however 80% of all flatworms are parasitic in nature.

Complete answer:
To begin with we know that flatworms belong to the phylum platyhelminthes which also include tapeworms as flukes. This phylum comprises around 13000 species, many of which acquire aquatic environments. These are mostly parasitic in nature. They possess bilateral symmetry and are triploblastic.
Let us discuss each to get to our answer-
Taenia- this is a tapeworm which belongs to the order cyclophyllidea and genus Taenia. It is an intestinal parasite that causes taeniasis and cysticercosis in cattle.
Fasciola- it is a liver fluke, in the genus parasitic trematodes. These are found in the bile ducts and liver of infected people and animals like cattle and sheep. It causes fascioliasis.
Pheretima- it is the genus to which earthworm belongs. They possess clitellum, which is a band of glandular tissue. These are present mostly in New Guinea and South-east Asia.
Planaria- this belongs to the class turbellaria. These are free-living freshwater flatworms. Their outer surface has cilia which helps in gliding over the surface of stones. They are scavengers and carnivores. It has the ability to regenerate i.e. when an individual is cut into several pieces, each piece is capable of forming an individual.

So, the correct answer is option A. Planaria.

Note:
Most Planarians occur in freshwater and even can be seen in huge masses, some species can be seen in marine water and others can be terrestrial. These are hermaphrodite i.e. possess both male and female sex are present in same individual.