The Order Hexanchiformes is a group of primitive sharks that includes species such as frilled sharks and cow sharks. They are characterized by having six or seven gill slits (instead of the usual five in most sharks) and a single dorsal fin positioned far back on the body. Hexanchiform sharks are generally deep-sea dwellers, with elongated bodies and sharp, comb-like teeth adapted for gripping slippery prey. They are considered living fossils, retaining many ancestral features of early sharks, and play an important role as apex or mesopredators in deep-ocean ecosystems.