Anatomy
P
Placoid Scale
/ /ˈpleɪkɔɪd skeɪl/ /
Etymology:
From Greek plax - "flat plate"
Quick Definition
The tooth-like scales of sharks and rays, composed of dentine and enamel — homologous to vertebrate teeth.
📖 Full Definition
Placoid scales (dermal denticles) are the scales of cartilaginous fishes (sharks and rays). Each denticle consists of a base plate of dentine embedded in the dermis, with a pulp cavity and an enameloid crown projecting backwards. They are homologous to vertebrate teeth and grow individually — sharks do not moult like bony fish. The ribbed surface texture of denticles reduces turbulent flow, a property mimicked in swimsuit technology. Denticle morphology varies by body region and is diagnostic at species level.
💡 Examples & Context
Shark skin feels smooth when stroked from head to tail (scales lie flat), but like sandpaper in the opposite direction.
✏️ Also Written As
Alternative spellings / forms
dermal denticle