Answer : 2. "Porifera"
Explanation :

1. Sponge belongs to Porifera phylum of the animal kingdom.

2. These are primitive multicellular animals. The study of sponges is known as para zoology.

3. Sponges are mostly irregular in shape and have radial symmetry.

4. The body of a sponge has two layers-

- Epidermis: This is the outer layer that helps move water in and out.

- Mesohyl: This is the middle layer which contains the cells of the sponge.