i think they just dont have arms but have legs
Here is my known list:
Dragons-2 fore-arms, 2 legs, and wings
Drakes-Wingless Dragons
Wyrms- Dragons without appendages.(arms, legs, wings)
Leviathans- Like Wyrms, although they may have arms. Also known as sea sea serpents.
Wyverns- Dragons without arms, but have the largest wings.
Hydras- Dragons with more than 1 head, not to be confused with the snake.
Dragon Turtles- Think bowser, dragons with a large shell.
Amphitheres- Wyrms with wings, may be bigger than a Wyvern's.
Asian dragons are basically Wyrms with appendages I guess, I don't bother with them because I have mixed feelings about them.