Unchanged for hundreds of millions of years, and having no close relatives on the evolutionary tree, the sponge remains a simple and primitive form of animal. Sponges have a remarkable ability to withstand enormous loss of body material, suddenly growing many times faster than normal to regain the original size. It is even possible that certain types of sponges to be passed through a fine sieve, their bodies broken down to the components cells, and reform themselves again over a period of hours or days. The average lifespan for individual specimens has been estimated to be 50 years or more.
The simplest type of sponge is shaped somewhat like a vase, with feeding cells on the interior wall. Water is drawn through minute pores in the outer wall and expelled through the large principal aperture. The present is preserved by the feeding cells, each with a tiny whip that’s waved always back and forth. Because of the huge volume of water contained inside the room in proportion to the inner wall surface of feeding cells, higher types of sponges have adapted by folding out the inner walls to increase the feeding area.
On low tide areas of the beach may be found lots of the flat in crusting sponges. These appear in a wide array of colours and have no definite shape of their own, instead taking on the kind of the rock beneath.
Some kinds of sponge are capable of releasing a noxious substance to prevent the encroachment of neighbours, and several of these poisons are used in research laboratories for the preparation of human medications.