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Bath Sponge

Spongia offinalis


The "skeleton" of a living bath sponge is purplish in color. Gaps in the skeleton are filled with a yellowish flesh. Bath sponges can reach diameters of 20 inches or more.

Bath Sponge in natural surroundings

Distribution and Habitat

Bath sponges are found in warm seas only, at depths down to 600 feet. They are most numerous in the Mediterranean, particularly the eastern half, and in the waters off the Bahamas and Florida.


A sponge normally draws all it needs from the sea without departing from the spot on which the larva settled. Sponges are almost completely still once the free-swimming larva has settled on a solid substratum, but some young sponges may actually move in response to adverse conditions.


Sponges are particulate feeders. The beating of flagella of its collared cells draws in currents of water. These enter through many minute pores in the skin. Having passed through these chambers the water is driven towards the surface and expelled with moderate force through crater-like vents. In its course through the sponge the water yields food particles and oxygen, and it leaves bearing waste products of digestion and respiration.

flagellated chambers magnified 260 times
flagellated chambers magnified 260 times


There are no males and females, ova and sperm being found in the same individual. At various points in the body of the bath sponge, some of the body cells are fed by neighboring cells so that they grow noticeably large. Some of these cells will eventually become egg cells. The others subdivide repeatedly until masses of tiny cells are found. These are the sperm, and, when ripe, they burst from their capsule into the water canals and escape by the vents into the sea. They swim around until near another sponge and are drawn in by the water current entering its pores. Inside, they travel through the canals until they meet an ovum, which one of them fertilizes.

Once fertilized, the ovum begins to divide repeatedly to form an oval mass of cells -- the embryo. Some of the cells put out flagella, and as they beat together, they cause the embryo to rotate. This breaks its capsule, and the embryo is now a free-swimming larva, which swims out through one of the vents. The larva will spend the next 24 hours swimming in a spiral motion. Then the flagella begin to weaken, the larva sinks to the sea bed, and is transformed into a small platelet of tissue, the size of a pin head. This is what grows into a full-size sponge.

From Sea to Bath

It takes seven years for a sponge to grow large enough to be harvested. It is the skeleton of a bath sponge that becomes the familiar natural bath sponge. In the "old days" sponges were cut from the sea bed, but today most are raised on "sponge farms."

a prepared bath sponge
a prepared bath sponge

the collared cells after the sponge has been prepared for human use
the collared cells after the sponge has been prepared

Scientific Classification

phylum Porifera
class Demospongiae
order Dictyoceratida
family Spongiidae
genus & species Spongia officinalis

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The Robinson Library >> Phylum Porifera

This page was last updated on 09/29/2018.