Rays protrude their jaws from flattened cartilaginous bodies
Batomorphs—rays—are cartilaginous fishes sometimes ranked as superorder Batoidea; Fishes of the World treats them as division Batomorphi. Like sharks they lack true bone. Most are flattened disc-shapes that live on sea floors from coasts to depths of at least 3,000 metres.
Rays are the most species-rich group of cartilaginous fish, with well over 600 species in 26 families, and together with the sharks they make up the elasmobranchs. Their skeletons are tough, flexible cartilage rather than bone. Most are flattened top to bottom into a cloak-like disc, the pectoral fins spread into broad wings, and there is no anal fin; guitarfishes and sawfishes are the less flattened exceptions. The mouth sits underneath, and many can shoot the upper jaw forward from the skull to grab food.
Diet shapes the teeth. Most species have heavy, rounded crushers for cracking snails, clams, oysters and crustaceans on the bottom, whereas manta rays strain plankton in open water. Bottom living is the norm, chiefly in warm coastal seas, though some live at least 3,000 metres down and a few tolerate brackish estuaries or fresh water.
Fertilisation is internal, which saves sperm and keeps eggs away from predators. Skates and some rays lay eggs in leathery cases, the mermaid's purses that wash up empty on beaches, while other rays carry young in a womb until birth. Being caught can make pregnant females abort or give birth early; this has been documented in at least 88 live-bearing shark and ray species, about 12 percent of them, yet fisheries rules seldom take it into account.
Molecular data rule out the old idea that rays are modified sharks. A 2011 DNA study of 37 taxa confirmed that skates, stingrays and electric rays each form natural groups but split the guitarfishes and sawfishes into two separate lineages. The Mesozoic sclerorhynchoids, with sawfish-like snouts, were once thought to be sawfish relatives and are now classed as true skates. Modern catalogues list families from torpedo rays and fiddler rays to wedgefishes and pygmy skates.
Source: Batomorphi
