I think it's safe to say that the big-headed turtle (Platysternon megacephalum) gets its name from... well... its BIG head! Interestingly enough, these turtles have such large heads that they cannot actually pull them back (withdraw) into their shells! They are easily recognizable in the wild - both because of their large heads and because of their very long tails!
These turtles range from dark gray-yellow to brownish in colour. Since they cannot protect their heads within their shells, these turtles protect themselves with a very strong bite! They have powerful jaws and a (cute) tip in the front of their heads, kind of like a bird's beak!
The big-headed turtle's carapace (or, hard shell) can measure up to approximately 20 cm! Like mentioned before, the big-headed turtle has a recognizably long tail. With this said, a big-headed turtle's tail can be almost as long as it's shell!