It usually looks like a thick bready crust with 'volcano' chimneys. Those are the excreting pores. The breadcrumb sponge has a strange smell, similar to exploded gunpowder. In reality, it is a material produced by the sponge itself to keep others from munching on it.

During low tide, you can find this remarkable sponge on jetties and under stones.

Filters plankton and bacteria out of the water.

Breadcrumb sponge reproduces both sexually and asexually. It releases eggs and sperm into the water, which fuse into larvae and eventually establish themselves as new sponges. Asexually, the sponge pinches off a piece of itself which attaches elsewhere and continues growing as a new sponge. A natural way of cloning.

http://eol.org/pages/1163432/overview (accessed 17/10/14)