Free standing: (not found around the Maltese Islands)
These sponges have more inner volume compared with their outside surface area and sometimes grow into strange shapes, often reaching gigantic proportions.
While not all sponges are as colorful or as large as those found in the tropics, sponges are an ancient and efficient design which will probably continue to populate the world's oceans longer than people will populate the Earth.
Encrusting sponges
Typically cover the surface of a rock in the same manner that moss covers a rock on land.
How do sponges reproduce?
Most sponges are hermaphroditic (having both sexes in one), but produce only one type of gamete per spawn. (they may play the male role one time and the female role the other time). The sperm is released into the water column by the "male" sponge and finds its way to the "female" sponges, where fertilization occurs internally. The planktonic larvae are released from the female sponge and float around in the water for a few days then settle down and start growing.
There are many different types of sponges which come in two basic types: encrusting or free-standing. Although neither of these names are part of the true classification of sponges, it does make it a bit easier to organize them.
Marine Life
SPONGES
A sponge is a bottom-dwelling creature which attaches itself onto something solid in a place where it can, hopefully, receive enough food to grow. The scientific term for sponges is Porifera which literally means "pore-bearing."A 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 sponge, chambers are lined with specialized cells called choanocytes, or collar cells which serve two purposes. First, they beat their flagella back and forth to force water through the 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 (like bacteria) brought in with the water. Sponges are very effective filter feeders.The "skeleton" of the sponge is composed of tiny needle-like splinters called spicules, a mesh of protein called spongin, or a combination of both. When all living tissues are removed the skeleton remaining is what we know as a sponge. Many sponges can only be identified by microscopic examination of the skeleton, which makes certain identification from photographs difficult.
There are approximately 15,000 different species of sponges in the world, 150 of which occur in freshwater. Only about seventeen are of commercial value. Although they may look plant-like, sponges are the simplest form of multi-cellular animals.
