ALTHOUGH THEY may look plant-like, sea sponges are the simplest of multi-cellular animals. A sea sponge is a bottom-dwelling creature, which attaches itself to something solid in a place where it can, hopefully, receive enough food to grow. The scientific term for sea sponges is Porifera, which literally means "porebearing." A sea sponge is covered with tiny pores, called ostia, which lead internally to a system of canals and eventually out to one or more larger holes, called oscula. Within the canals of the sea sponge, chambers are lined with specialized cells called choanocytes, or collar cells.

The collar cells have a sticky, funnel shaped collar and a hair like whip, called a flagellum. The collar cells serve two purposes. First, they beat their flagella back and forth to force water through the sea sponge. The water brings in nutrients and oxygen, while it carries out waste and carbon dioxide. Second, the sticky collars of the collar cells pick up tiny bits of food brought in with the water. Another type of cell, called an amebocyte, takes the food to other cells within the sea sponge. Sea Sponges are very effective filter feeders, since they are able to capture and eat particles as small as bacteria as well as much larger particles. The "skeleton" of the sea sponge is composed of tiny needle-like splinters called spicules, a mesh of protein called spongin, or a combination of both. Many sea sponges can only be identified by microscopic examination of the skeleton, which makes certain identification from photographs difficult.

There are many different types of sea sponges in the world's oceans, and, contrary to popular belief, they can be quite colorful and beautiful. Sea Sponges come in two basic types: encrusting or freestanding. Although neither of these names are part of the true classification of sea sponges, it does make it a bit easier to organize them.

Encrusting sea sponges typically cover the surface of a rock in the same manner that moss covers a rock on land. Freestanding sea sponges are a bit more interesting. These sponges have more inner volume compared with their outside surface area and sometimes grow into strange shapes, often reaching gigantic proportions.

Many of the freestanding sponges are well known to most people. For example, nearly everyone has heard of the barrel sea sponge, a large tropical sponge that sometimes grows large enough to fit a whole person inside. Equally well known are the tube sponges of the tropics, coming in nearly every color of the rainbow.

Here are some examples of sea sponges:

Famous Sea Sponges

Tube Sponge

The Tube Sponge is one of the most common varieties of sea sponge to be found on the reef. It is distinguished by its long tube-shaped growths, and ranges in color from purple to blue, gray, and gray-green. Filtered water is ejected through the large openings on the ends. This is one of the few reef invertebrates that is blue in color.

Vase Sponge

The Vase Sponge is a common species found in the Caribbean off the eastern coast of Florida. A large bell shape with a deep central cavity characterizes it. This sea sponge grows up to 2 feet wide and 3 feet high. It ranges in color from purple to red and brown, and is found attached to rocks near the sandy bottoms.

Yellow Sponge

This small Yellow Sponge species is commonly found throughout the Pacific coastal waters of the United States. It is found growing in small colonies, and ranges in color from orange to bright yellow. This sea sponge and can be found encrusting rocks on the reef face.

Red Tree Sponge

This bright red sponge species is very common throughout the Caribbean Sea. This sea sponge usually grows to a height of about 8 inches. This is one species that is easy to keep and can do relatively well in a home aquarium environment. These sponges require a moderate water flow and dim light to do well.

Common Sea Squirt

This species of sea squirt is very common on the reef, and is usually found in deep water. It can be found encrusting the rocks in large colonies. This squirt's leathery bag-like body has a white and gray or brown spotted exterior with a bright green interior. It is sometimes introduced into the aquarium on live rock.

Painted Tunicate

The tunicates are very similar to sea squirts. They take water in through a large opening where nutrients are filtered out. The water is then expelled through another opening. Painted tunicates are about 3/4 inch long and commonly grow in colonies. They are found in translucent red, purple, and yellow colors.

If you would like to learn more about the sea sponge and I am not talking about Sponge Bob, go to your local library or online where you can find loads of information on them.