a primitive sedentary aquatic invertebrate with a soft porous body that is typically supported by a framework of fibers or calcareous or glassy spicules. Sponges draw in a current of water to extract nutrients and oxygen.
Other images are just as mystifying the spine of a sea urchin, sharks' teeth, sponges and ascidians, to name a few.
a piece of a soft, light, porous substance originally consisting of the fibrous skeleton of an invertebrate but now usually made of synthetic material. Sponges absorb liquid and are used for washing and cleaning.
This increases insulation and avoids the need for surface treatment, while the vegetation absorbs rain like a sponge , reducing or at least delaying run-off.
a person who lives at someone else's expense.