____________ are commonly known as comb jellies.

Ctenophora

The correct answer is Option (3)- Ctenophora

Ctenophora are commonly known as comb jellies.

Ctenophores, commonly known as sea walnuts or comb jellies are exclusively marine, radially symmetrical, diploblastic organisms with tissue level of organisation. The body bears eight external rows of ciliated comb plates, which help in locomotion. Digestion is both extracellular and intracellular. Bioluminescence (the property of a living organism to emit light) is well-marked in ctenophores. Sexes are not separate. Reproduction takes place only by sexual means. Fertilisation is external with indirect development.
Examples: Pleurobrachia and Ctenoplana.