Unlike females, the males bear a pair of flagella, one on each chelicera. They all have a serrated keel on the retromargin of each chelicera. This type of chelicera occurs exclusively in the Tetrapulmonata. Males have sharp, forward-pointing tooth under first segment of chelicera. Unlike other mygalomorph spiders, the Ctenizidae have a on the chelicera. Jackknife chelicera presents two different forms&colon; orthognathous and labidognathous. This kind of chelicera is rotated and occurs exclusively in the Araneomorphae spiders. The chelicera usually has a tooth with two cusps on the rear-facing edge.