Chimaeras (keye-meer-uh) are cartilaginous fish related to the sharks & rays are sometimes called Ghost Sharks, Rabbitfish or Ratfish. Chimaeras live in temperate ocean floors down to 2,600 meters (8,500 feet) deep, with few occurring at depths shallower than 200 meters (660 feet). For defense, most Chimaeras have a venomous spine located in front of the dorsal fin. This strange cartilaginous fish uses its long snout to scan over the sea floor for the electrical impulses of its prey that bury in the muddy sea floor, just like a metal detector. Chimaeras lay horny egg cases in which their young are left to develop, potentially for up to one year. On the whole, Chimaeras are rather peculiar-looking, deep-sea fishes. They have a disproportionately huge head (Holocephali means “whole head”) pocked with large, well-developed eyes. They have an odd, rabbit-like mouth filled with plate-like grinding teeth. The tail is tiny and often streamer-like, so for propulsion Chimaeras rely instead on flapping their large, wing-like pectoral fins. Chimaeras swimming motion resembles a kind of weird cross between a fish and an angel. Some 42 species of living Chimaera are known.
As the name Chimaera suggests, holocephalans combine an odd mix of characteristics. Among other features, they are characterized by: a gill cover over the 4 gills, leaving a single opening on each side of the head; the palatoquadrate (upper jaw) is usually fused to the cranium; no spiracle opening behind the eye; branchial (gill) basket mostly beneath the neurocranium (posterior part of the cranium that encases the brain); teeth relatively few (1 pair in the lower jaw and 2 pairs in the upper), occurring as mineralized grinding plates; tooth plate replacement is slow; no cloaca, but with separate anal and urogenital openings; skin in adults ‘naked’ (without dermal denticles); no stomach or ribs; and males — in addition to the pelvic claspers — have an accessory clasping organ on the head.