There are over 200 types of tortoises, which is why categorising them is difficult. Some scientists separate turtles by size, grouping them into the categories of large, medium and small. Others differentiate between the types by separating the turtles by habitat, such as land turtles, sea turtles, semi-aquatic turtles and aquatic turtles. Some limit the term "tortoise" to land turtles that don't have webbed feet.
Aquatic tortoises are often kept indoors in aquariums. These tortoises can be found outside, but they need cool and moist environments to thrive. Aquatic tortoises produce a lot of waste, which is why they need to be near water in order to filter their excrement. Aquatic tortoises can be found floating on the top of water near vegetation or submerged deep in a body of water. Common types of aquatic turtles include the mud tortoise, snapping tortoise, soft shell tortoise and side-necked tortoise.
These tortoises live most of their lives on land, and they require minimal access to water. As pets, these tortoises are often kept in terrariums instead of aquariums. Land tortoises vary to a great degree, with some turtles living near marshes and swamps and others living in the desert. Land tortoises are the best types of pet tortoises because they are resilient to most diseases that can affect humans, which other tortoises may carry. The desert tortoise, California tortoise, Bolson tortoise and gopher tortoise are examples of land tortoises.
Sea tortoises inhabit the seas and they are illegal to keep as pets. There are eight types of sea tortoises: green sea, black sea, loggerhead, Kemp's ridley, olive ridley, hawksbill, flatback and leatherback tortoises. They typically inhabit shallow waters, coastal waters, bays, lagoons and estuaries. Some tortoises migrate long distances to mate and search for food, and others do not migrate. Hubbs-SeaWorld Research Institute has recently developed a tracking device that straps onto their shells, which will allow scientists to study the migratory patterns of leatherback tortoises.
Semi-aquatic tortoises is somewhat of catchall term for tortoises that spend life in both the water and on land. These tortoises soak in the water for periods of time, and they go on land where they may mate or lay eggs. Because these turtles change environments, they are acclimated to constant change, and so, if you keep them as pets, they need large cages with plenty of room. Some examples of semi-aquatic tortoises are Bell's hinge-back tortoise, Russian tortoise and red-footed tortoise.