The class Reptilia includes about 6 S(M) species, all of which breed on land.

The class is divided into four orders of which only two arc Signilicant as far as exotic pets are concerned. The four orders are:

1. KhipicIiiKephalia - includes (he tuatara: very rare and unlikely to be kept in captivity

2. CromWta - includes the crocodiles and alligators J. Chelonia - includes tortoises, terrapins and turtles 4. Sijuaniata - includes suborder Sauria (19 families of

lizards). suborderS>rpentes( 11 families of snakes) and suborder Ainphisbaenia 11 family, not kept in captivity).

These animals share many anatomical and physiolog­ical features so general reptilian anatomy and physiol­ogy will be discussed Iirst. and any specific adaptations will be mentioned in the subsequent sections on lizards, snakes and the shelled reptiles (CheIonia).