Zool. of or having scales that are periodically shed and replaced, consisting of a dentin base and an enamel-covered surface, as in cartilaginous fishes
Origin of placoid; from Classical Greek plax, flat plate, tablet (see placenta) + -oid
- a. Relating to or being a kind of fish scale that is a toothlike plate with a protruding spine, characteristic of sharks, skates, and rays.b. Having placoid scales.
Origin of placoidGreek plax, plak-, flat stone, plate; see plak-1 in Indo-European roots + –oid.
- Platelike; having irregular, platelike, bony scales, often bearing spines; pertaining to the placoids.
- Any fish having placoid scales, such as the sharks.