Placoid :: Placoid (a.) Platelike; having irregular, platelike, bony scales, often bearing spines; pertaining to the placoids..
Placoid :: Placoid (n.) Any fish having placoid scales, as the sharks..
Placoides :: Placoides (n. pl.) A group of fishes including the sharks and rays; the Elasmobranchii; -- called also Placoidei.