Sponges are sessile filter feeders and they grow in large populations in most environments and conditions.  Being a filter feeder, they rely heavily on water movement to bring in a good supply of debris and marine snow.  Sponges can be found in coral reefs as well as rock reefs.  They are seen in many colors, shapes, and sizes.  The main characteristic of  Sponges would be that they have an intake and outlet for which they process the food they consume.