Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines. There are seven extant species of sea turtles: the green, loggerhead, Kemp's ridley, olive ridley, hawksbill, flatback, and leatherback.Four of the species have been identified as "endangered" or "critically endangered" with another two being classed as "vulnerable".