TURTLE AND TORTOISE TAXONOMY:
Kingdom: Animalia ("animals" and insects)
Phylum: Chordata (has a backbone)
Class: Reptilia (not amphibians)
Order: Testudines (turtles and tortoises)
Most terrestrial turtles sold in pet shops get large, most around 10 inches in shell length. For a turtle such as a box turtle, you will need a cage 50 - 100 gallons once they reach their max size. With turtles, ground space is what is important, not height. With turtles, it would almost be best to build your own cage. This way your turtle could have more ground space than what a conventional glass tank could provide.
PROPER LIGHTING -
With all reptiles, especially turtles, it is crucial to have proper UVB exposure. A turtle's shell is made of two things; keratin (same material as your fingernails) and Calcium (Bone). UVB helps with proper bone development. A turtle who lacks UVB exposure will soon develop holes in his shell (carapace - top section, and plasteron - bottom section). During the warmer months, it is perfectly fine to let your turtle roam around outside (as long as no poisons have been used in the area and he's under supervision). The claws on a turtle are not for decoration; if unsupervised you might find a tunnel in your yard and no more turtle. In addition to UVB, it is equally important that your turtle gets enough UVA and heat. UVA rays stimulate both eating and mating behavior in reptiles. Heat is needed for proper digestion. Keep the cage around 75F-85F during the day.
Land turtles are vegetarians. They need fruits and vegetables. Provide fresh food daily. Turtles, as with any reptile, it is a good idea to lightly dust their food with a reptile vitamin supplement. For turtles, you want one that has both calcium and vitamin D3 in it. Most if not all the vitamins should contain both of these, but be sure to check anyways.
Aquatic turtles, just like the terrestrial turtles also get large, again about 10 inches in shell length. Housing for aquatic turtles such as the popular Red-eared slider are very similar to land turtles as well. Cage requirements are the same, but instead of substrate, you would obviously use water. For water depth, you want it deep enough so that the turtle can completely submerge. It is CRUCIAL that you provide a rock or something for them to bask on. The basking rock needs to allow the turtle to come COMPLETELY out of the water. If the turtle is not allowed to completely come out of the water, he will develop a respiratory infection.
Proper Lighting -
The lighting is the same as with land turtles.
Aquatic turtles will eat live fish and commercial turtle pellets. Young turtles should get small minnows, larger turtles get larger feeder fish. Feed him about 6 live fish (Adjust quantity accordingly) once a week and feed him pellets every other day. Feed roughly 10-15 pellets when young, increase quantity with age (Adjust quantity accordingly).
DIFFERENCES IN LIGHTING (All Reptiles):
UVB helps reptiles with proper bone development. UVA stimulates reptiles to both eat and reproduce. Most light bulbs put off at least some UVA, especially the heat lamps. The heat lamps are needed for reptiles to properly digest their food.