Most species of Bryozoan live in marine environments. There are about 50 species which inhabit freshwater. In their aquatic habitats, bryozoans live on all types of hard substrates: sand grains, rocks, shells, wood, blades of kelp, pipes and ships may be heavily encrusted with bryozoans. Some bryozoan colonies, however, do not grow on solid substrates, but form colonies on sediment. While some species live at depths of 8,200 m, most bryozoans live in much shallower water. Most bryozoans are sessile and immobile, but a few colonies are able to creep about, and a few species of non-colonial bryozoans live and move about in the spaces between sand grains. One remarkable species makes its living while floating in the Southern Ocean. Several bryozoan species live in the Midwestern United States, especially in Ohio, Indiana, and Kentucky which was once a part of a large ocean, the Western Interior Seaway.