PHYLUM PORIFERA
The name ‘Porifera’ comes from the Latin word ‘porus’ meaning ‘pore’ and ‘ferre’ meaning ‘to bear‘,
so it means ‘a pore-bearing organism’. The Phylum Porifera consists of sponges. They are multi-
cellular with no organs, no nervous, digestive or circulatory systems. Their bodies do not have a
de)nite symmetry. Also, they do not have a true body cavity but a water-)lled space inside. All
sponges are sessile, and all are )lter-feeders. There are approximately 7000 living sponge species in
the Phylum Porifera, 2% of which are freswater sponges, and none terrestrial. One of the main
characteristics of sponges is their unique feeding system. The sponges may reproduce sexually or
asexually, and they have a larval stage which is planktonic. As the sponge cells are not linked in a
tissue, they can be moved apart, and they can come together again and continue functioning or even
make a new sponge from the remaining part.
THE STRUCTURE OF THE SPONGE -THE FORM AND FUNCTION OF THE BODY WALL
Sponges consist of relatively few cell types. The outermost layer of the body is made up of
PINACOCYTES which have the function of epidermal cells in animals. They are the most tissue-like
material of sponges. Pinacocytes are thin, leather-like and a very closely packed layer of cells that line
the exterior and some interior surfaces of a sponge. They can change their size by contracting, and in
this way, the size of the openings on the surface can be changed to control the 9ow of water.
CHOANOCYTES, also called collar cells, are specialised feeding cells which are vase-shaped with a
collar of )ne )brils connected by microvilli. A single 9agellum extends from the center of the collar,
and water is driven through the sponge by the beating of the numerous 9agella. The collar works as a
)lter to strain food items from the water pumped in, and even very small items such as bacteria can
be )ltered.
Between the pinacocytes and choanocytes is a space called MESOHYL (or mesenchyme) which
consists of a proteinaceous, gelatinous matrix, some cells and spicules. SPICULES are a major part of
the skeleton of a sponge. They have a spine or ray shape radiating from the center. They consist of an
organic material covered with calcium carbonate or silica.