Tortoises and turtles are called Chelonia.

In the order Testudines (tortoise-like or turtle-like), there are two suborders: Cryptodira (hidden neck) and Pleurodira (side neck).

Cryptodira means that the chelonians pull their neck right into their shell—most chelonians are in this category. Their necks go in and out.

Pleurodira means that the chelonians tuck their neck sideways under their shell.

There is a space or overhang between the top shell and the bottom shell – in front of one of the front legs – where the necks of Pleurodira chelonians are protected.

Pleurodira chelonians mainly live in the Southern Hemisphere, in Australia, South America and Africa.

Cryptodira chelonian – its head can be retracted into its shell

Cryptodira chelonian – its head is retracted into its shell

A Pleurodira chelonian

A Pleurodira chelonian with its head sideways underneath its shell

The difference between a Cryptodira and a Pleurodira

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM