Turtles (Testudines) are reptiles. There are only about 320 species of turtles existing today! This may seem like a lot to us, but since other groups of reptiles like lizards and snakes have numbers of species in the thousands, this number is very small!
Turtle species are usually split into two main categories: Cryptodira and Pleurodira. Cryptodira are made up of turtles who can retract their heads in backwards - within this species are the Chelonioidea, Testudinoidea, and Trionychoidea! Pleurodira species retract their heads in sideways - within this species are the Chelidae and the Pelomedusidae.
A turtle's body is made up of two parts. The upper part is called the carapace (or, shell). The lower part is called the plastron (the underside of a turtle). These two parts link together, kind of like a puzzle, and form what are called bridges! That's why, a turtle's shell looks as if it wraps all the way underneath!
A turtle's shell is its home! With the exception of sea turtles, most turtles can hide within their shells! Sea turtles heads and limbs cannot go inside their shells.
The outer part of a turtle's shell is made up of plates (that kind of look like floor tiles!) that are joined together in unique patterns. These plates are called scutes. Scutes are actually part of the turtle's skin so they are always growing. Sometimes these scutes are neatly joined side by side and sometimes they overlap one another - this is why some turtles have humps and bumps and spikes! But basically, they are just like very large lizard scales! And similar to a snake, some turtles can actually shed their shell scutes entirely!
Underneath the scutes (the skin layer) is another layer of plates. This layer is made up of... bone! The average turtle has about 59 of these bone plates: 50 in the carapace and 9 in the plastron.
These bone plates are mismatched (or staggered) underneath the scutes - this gives the turtle's outer layers amazing strength against predators, competition, and dangerous environments.
Turtles do not have teeth! However, they still have some serious bite!
Some turtles snap and others (like the Mata Mata) have a very weak bite and rely on extreme sunction to eat their food!
Turtles lay eggs! Some turtles lay their eggs in sand and abandon them (like the Olive Ridley sea turtle). Some turtles lay their eggs along the water's edge in nests and remain nearby and return annually for mating (like the Diamondback terrapin).