Turtloid, referred to as Dawson (ドースン) in the Japanese manual, is a badnik from the 16-bit version of Sonic the Hedgehog 2 found in Sky Chase Zone. These are pretty easy to get rid of; just jump on the little turtle. The badnik attacks by pulling a handle, causing the bigger turtle to fire a bullet from its mouth. Once the smaller turtle is destroyed, the larger turtle becomes a stationary platform.
Turtloids return in Sonic the Hedgehog 4: Episode II, flying high in the skies as part of Metal Sonic's fleet in Sky Fortress Zone Act 1. This time, however, the Tornado cannot pass through the bigger turtles, and at a certain point in the Act, Sonic is required to step across them to get from one side to the other.
A similar badnik, known as an Armadiloid, appears in Sonic Mania's Mirage Saloon Zone.