Cockatrice and Basilisk: iconic D&D monsters over the decades. While these are depicted in later editions as a rooster like serpent and multi-legged lizard respectively, one should note there is no explicit description for either. The Cockatrice is said to be able to fly, it is noted the basilisk cannot. Volume III, page 7 features an illustration of a basilisk we can best describe as dragon-like dog creature.
Gorgons: though most persons associate the word Gorgon with snake-haired Medusa and her two sisters? Gygax was familiar with a less well-known reference to a scaled bull which fed on poisonous herbs giving it a lethal breath.
Hydras: a multi-headed dragon like creature. In A&D the beast would evolve into three types drawn from mythology.