The correct answer is C. Porifera.
Sponges are simple animals that lack true tissues or organs. They are filter feeders, meaning that they take in water and food particles through pores in their bodies. Sponges are found in all oceans of the world, from the tropics to the poles. They can live in shallow water or deep water, and they can be found on the seafloor or attached to rocks or other objects.
There are over 5,000 species of sponges. They are classified into three main groups: glass sponges, demosponges, and hexactinellids. Glass sponges are the most primitive group of sponges. They have a skeleton made of silica, which is a type of glass. Demosponges are the most common group of sponges. They have a skeleton made of spongin, which is a protein. Hexactinellids are the least common group of sponges. They have a skeleton made of silica spicules, which are needle-like structures.
Sponges play an important role in the marine ecosystem. They filter water and remove pollutants. They also provide food and shelter for other marine animals.
Option A is incorrect because protozoa are single-celled organisms. Option B is incorrect because annelids are segmented worms. Option D is incorrect because cnidarians are radially symmetrical animals with stinging tentacles.