Helmethead Gecko

The adult helmethead gecko has a snout-to-vent length (SVL) of 7.5 cm (3.0 in) and a total length of about 11 cm (4.3 in). The head is covered with small granulations and the tubercles at the back of the head are enlarged and form a casque. The digits are flattened and spatulate. Dorsally, the helmethead gecko can be from light grey to dark brown, either uniform in color or with pale or dark blotches. The underside is light-colored.

T. chazaliae is mainly nocturnal, and whereas most lizards are diurnal and have lost the rod structures in the retina that is typical of vertebrates, retaining only cones, this gecko has further adapted its eyes so that it has some degree of color vision at night. The gecko has developed a multifocal optical system which enables it to distinguish between light at different wavelengths. The pupils of this gecko are circular during the night but take the form of a pair of pinhole size pupils in each eye during the day. The precise function of this change is unclear, but it has been suggested that the pinhole pupils may be less visible to potential predators while the lizard is basking in the sun. Helmethead geckos are the first known vertebrates which are able to see color at very low levels of light, and their acute color vision at night is 350 times better than that of humans.

The specific name, chazaliae, is in honor of the yacht Chazalie, which belonged to French naturalist Raymond Comte de Dalmas (1862–1930), who collected the holotype. The common name, helmethead gecko, derives from the shape of the head caused by some of the scales at the back of it.