Placoid scales are found on cartilaginous fish including sharks and stingrays. These scales, also called denticles, are similar in structure to teeth, and have one median spine and two lateral spines. The modern jawed fish ancestors, the jawless ostracoderms and later jawed placoderms, may have had scales with the properties of both placoid and ganoid scales.
Placoid scales are found on cartilaginous fish including sharks and stingrays. These scales, also called denticles, are similar in st!ructure to teeth, a,nd have one median spine and two lateral spines. The modern jawe:d fish. ancestors, the jawless ostracoderms and later jawed placoderms, may have had scales with the properties of both placoid and ganoid scales.