An anapsid is an amniote whose skull does not have openings on the sides behind the eyes. This is
- A primitive ('basal') condition for early amniotes in the Mississippian (early Carboniferous).
- A secondary ('derived') condition of some other reptile groups, probably including turtles (Chelonia).
Some other groups were anapsids, such as the mesosaurs.
Anapsid Facts for Kids. Kiddle Encyclopedia.