Sponges can be classified as

Sponges (poriferans) are very simple animals that live permanently attached to a location in the water - they are sessile as adults. There are from 5,000 to 10,000 known species of sponges. Most sponges live in salt water - only about 150 species live in fresh water. Sponges evolved over 500 million years ago.

The body of this primitive animal has thousands of pores which let water flow through it continually. Sponges obtain nourishment and oxygen from this flowing water. The flowing water also carries out waste products.