People have cartilage in their outer ears and soft tips of noses, but our bones are made of calcium phosphate and living tiss ue. The cartilage in rays and sharks is more flexible and lightweight than bone. Some parts of cartilaginous fish, such as the skull and vertebrae, are strengthened with calcium which protects vital systems. Sharks have tough skin covered with rough modified scales, called dermal denticles. They make the skin of sharks feel like sandpaper.
Rays have no or greatly reduced dermal denticles and feel soft and smooth.
The winglike pectoral fins have a net-like framework of cartilage that provides support but allows a wide range of motion. The upper surface of the animal ranges in color from light to dark solids, and some even have patterned spots. The undersides are lighter. Although rays are good swimmers, most of them are geared to a bottom-dwelling lifestyle. All but manta rays have a mouth on the underside of their head.