Worms are barely evolved soft-bodied animals. They are more common in aquariums
as live food than as residents, but are never found in freshwater aquariums.
A few specific species can be kept in captivity in sea water. They live in a
tube and are often sedentary. The coloring of worms can vary enormously, but they
are usually blue or purple, flecked with white, and almost always bicolor.