The appearance of the Breadcrumb Sponge (Halichondria panicea) varies from thin sheets to thick crusts and large lumps. On wave-exposed shores, it usually grows under ledges as a thin, green crust, its osculae opening at the tops of small mounds. Its green color is produced by photosynthetic pigments in symbiotic algae in the sponge&amp;#8217;s tissues. In deeper, shaded waters, the sponge is usually a creamy yellow. In waters with strong currents, this sponge may cover large rocky areas and kelp stems.