Sponges are the simplest form of multi-cellular animals. A sponge is a bottom-dwelling creature which attaches itself to something solid in a place where it can find enough food to grow. The scientific name for sponges is "Porifera," which translates into "pore-bearing."

A sponge exists by pumping water through its body. A sponge is covered with tiny pores which lead internally to a system of canals and eventually out to one or more larger holes. These canals exist to move water through the sponge's body. Lining these canals are special collar cells. The collar cells force water through the sponge which brings oxygen and nutrients while removing carbon dioxide and waste. The collar cells are how sponges feed. The water brings with it bacteria and other organisms which the cells capture and filter out.

How Do Sponges Reproduce?
Most sponges are both male and female. During mating, one sponge plays the male role while the other plays the female role, even though both are capable of playing either role. A sponge may play a female role one time and a male role the next time. Sperm is released by the "male" sponge and enters the "female" sponge. After internal fertilization, larvae is released. After floating around for a few days, they settle down and start growing.

The Two Types of Sponges
There are many different types of beautiful and colorful sponges. The two basic types of sponges are: encrusting or free-standing. However, these are not part of the true classification of sponges (it just makes it easier for us to categorize them).

Encrusting sponges are similar to moss because they tend to cover the surfaces of rocks.

Free-standing sponges have lots of inner volume compared with their surface area. Sometimes, they grow into strange shapes and gigantic sizes.