In general, geckos may be divided into 2 primary groups: species with immovable, or fixed, eyelids (Gekkoninae, Teratoscincinae, and Diplodactylinae), and species which possess a movable eyelid (Aleuroscalabotinae & Eublepharinae). Geckos which possess fixed eyelids can be further divided on the basis of the presence (arboreal), or lack of presence (generally terrestrial), of sub-digital lamellae. Normally, the tail length of most gecko species is nearly equal to the snout-vent length and is expressed in a great variety of textures, shapes, and sizes. Additionally, the presence of either round pupils (diurnal) or vertically oriented pupils (nocturnal) helps to distinguish several genera. A number of arboreal species exhibit a stunning degree of beautiful green, red, and blue coloration (notably, species of Phelsuma and Naultinus). Finally, scalation characteristics range from the tile-like network (smooth, cycloid, imbricate) to be found on Teratoscincus, Geckolepis, and Teratolepis, to among some of the most minute, velvety-textured, granular scales exhibited in several Oedura species.
Among the genera which attain the smallest of size, the Sphaerodactylus species must surely be the most recognized, with several growing to only 30 mm in total length. The largest recorded species are Rhacodactylus leachianus, Gekko gecko, Gekko smithi, Uroplatus fimbriatus and Saltuarius cornutus, with total lengths in excess of 350 mm. Presently, Rhacodactylus leachianus is regarded as having the greatest snout-vent length of 240mm, with a tail length of less than the 50% of the snout-vent length. The largest known (recent) fossil species are Phelsuma gigas (total length more than 500mm) and Hoplodactylus delcourti (total length of the only known specimen measures 622mm). Both species are presumed extinct, yet the possibility for the continued existence of the latter has been recorded.