The other major subgroup of cartilaginous fishes, the subclass Holocephali, comprises about twenty-five or thirty living marine species, most or all of which are placed in a single family, the Chimaeridae. They have a single gill opening on each side, like the bony fishes, but unlike them have a soft (rather than bony) gill cover. These fishes, commonly called chimaeras or ratfish (because of their long, slender tails), live and feed on the ocean bottom, usually in deep water. They have pavementlike teeth for crushing their mollusk and crustacean food, and they have a venomous spine on the leading edge of the first dorsal fin (the forwardmost of the unpaired fins on the upper surface of the body) for defensive purposes. Male ratfishes have a fingerlike barbed clasper, of unknown function, on the top of the head, and two pairs of claspers on the ventral (belly) side of the body.At least one pair of these ventral claspers is involved in mating. The female lays eggs in leathery capsules somewhat like skate egg cases.
Thanks for description - Animal life club