The Scolecophidia, commonly known as blind snakes or thread snakes, are an infraorder of snakes. They range in length from 10 to 100 centimetres (4 to 40 inches). All are fossorial (adapted for burrowing). Five families and 39 genera are recognized. The Scolecophidia infraorder is most likely paraphyletic. The common name of Scolecophidia, blind snakes, is based on their shared characteristic of reduced eyes that are located under their head scales. These head scales are found in all snakes and are referred to as spectacles, but within this infraorder, they are opaque, resulting in decreased visual capabilities. Reduced eyes of the Scolecophidia have been attributed to evolutionary origins of snakes, which are hypothesized to have arisen from fossorial ancestors, causing a loss of genes related to eyesight that later evolved again in higher snakes to be similar to other vertebrates due to convergent evolution. Newer research shows that seven of the 12 genes associated with bright-light vision in most snakes and lizards are not present in this infraorder, and the common ancestor of all snakes had better eyesight. Other shared characteristics include an absent left oviduct in four of the five families, aside from the Anomalepididae, which have a well developed yet reduced left oviduct. Aside from this, these snakes range in length from 10 to 100 cm (3.9 to 39.4 in). Their typical body shapes include slender, cylindrical bodies and small, narrow heads. All these families either lack or have a vestigial left lung and lack cranial infrared receptors. (Source: Wikipedia.org, CC BY-SA)