Chimaerae

Chimaerae refers to an order of marine cartilaginous fishes, closely related to sharks and rays, but distinguished as the subclass Holocephali. Unlike sharks and rays, chimaeras possess a single external gill opening on each side of their body, covered by a flap.12

Key characteristics of chimaeras include:
* Cartilaginous skeletons.1
* Males have claspers for reproduction.1
* A unique supplemental clasping organ called a tentaculum on the forehead and in front of the pelvic fins.1
* Tapered bodies with large fins, large eyes, and two dorsal fins, the first with a sharp spine.1
* Slender tails, leading to the common name "ratfish" for some species.1

These fish are found in temperate to cold waters worldwide, inhabiting depths from coastal areas to over 2,500 meters. They are weak swimmers and feed on small fish and invertebrates. Females lay large, protected eggs. Chimaeras are thought to have originated after the Devonian extinctions, with the earliest fossil evidence dating back approximately 280 million years.1