(Of fish scales) tooth-like, being made of dentine with a pointed backward projection of enamel, as in sharks and rays. Compare with ctenoid and ganoid.
- Similar attempts had been underway in the dermal skeleton, stemming from Williamson's use of placoid scales from extant sharks as conceptual units in comparative analysis.
- The earliest attempts to unravel the nature of development and patterning of the vertebrate dermoskeleton and visceral skeleton place central importance upon the nature of the placoid scales in living sharks.
- Like other sharks, catsharks are covered with placoid scales.
Mid 19th century: from Greek plax, plak- 'flat plate' + -oid.
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