Sedentary, aquatic, filter-feeding METAZOA. The size ranges from millimeters to more than 1 meter in diameter, commonly 0.1-10 litres in volume. Consistency varies with nature and density of the skeleton from soft crumbly to stiff elastic and stony hard. Colours are often vivid (yellow, red, blue), particularly in dark locations; shades of green and brown are commonly caused by symbiotic algae. Sponges are crustose or massive, cushion, fan, tube, tree or cup shaped. Attached to the substrate, they show little movement except contraction of the entire body or of the openings upon disturbance.

Of the four recent sponge classes, the reef dwelling Sclerospongea have hitherto not been found on Bermuda and Hexactinellida occur in the deep sea. Of about 5000 species known, 70 (approximately, because of many uncertain identifications) are found in Bermuda.