A clade of jawless vertebrates—the ‘circle mouths’—comprising the hagfishes and lampreys. Hagfishes (class Myxini) have long eel-like bodies lacking fins and a lower jaw. They scavenge for food on the seabed, often feeding on dead fish and whales. The notochord is retained into adulthood, and they have a cartilaginous skull and only vestigial vertebrae; they are deemed to have secondarily lost such characteristic vertebrate features. When threatened, hagfishes secrete copious amounts of slime as a means of defence. Lampreys (class Petromyzontida) are wormlike animals that also lack jaws but possess cartilaginous projections, resembling vertebrae, from the notochord in adult life. Some species feed as parasites on fish, using their toothed circular mouth as a sucker to bore into their host and suck its blood. Free-living lampreys feed only during the larval stage (see ammocoete) and die shortly after achieving sexual maturity and breeding. See craniates.