 Substantial morphological variation (body size, colour and colour pattern) is evident within "O. n. nigriplantare", potentially indicating morphological evolution following its colonization of the Chatham Islands.Indeed, "O. n. nigriplantare" (up to 91 mm Snout to Vent Length; SVL) has a substantially larger body size than "O. n. polychroma" (up to 77 mm SVL).Recent genetic studies indicate that "O. n. nigriplantare" diverged from "Oligosoma nigriplantare polychroma" (its nearest relative) 5.86–7.29 million years ago.