Anatomy
G
Ganoid Scale
/ /ˈɡænɔɪd skeɪl/ /
Etymology:
From Greek ganos - "brightness, sheen"
Quick Definition
Heavy, rhomboid, non-overlapping scales with a layer of ganoine (enamel-like material) found in primitive ray-finned fishes.
📖 Full Definition
Ganoid scales are thick, diamond-shaped (rhomboidal) scales with a shiny, enamel-like ganoine outer layer over a layer of dentine and bone (isopedine). They fit together with peg-and-socket joints and provide heavy armour rather than the flexible coverage of cycloid or ctenoid scales. They are found in relict primitive fishes: gars (Lepisosteidae), polypterygiforms (bichirs), and sturgeons. In sturgeons the scales are modified into large bony scutes.
💡 Examples & Context
The heavily armoured alligator gar (Atractosteus spatula) has virtually impenetrable ganoid scales that were historically used by Native Americans as arrowheads.