placoid

American  

[plak-oid] / ˈplæk ɔɪd /

adjective

1. platelike, as the scales or dermal investments of sharks.

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placoid British  

/ ˈplækɔɪd /

adjective

1. platelike or flattened

2. (of the scales of sharks and other elasmobranchs) toothlike; composed of dentine with an enamel tip and basal pulp cavity

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Etymology

Origin of placoid

1835–45; < Greek plak- (stem of pláx ) something flat, tablet + -oid

Example Sentences

Researchers in this study also revisited an analysis of fossilized placoid scales, or tiny tooth-like scales that cover sharks, from the megalodon.

From Salon • Mar. 10, 2025

Shark teeth likely evolved from the jagged scales that cover their skin, called placoid scales.

From Textbooks • Jan. 1, 2015

An important feature is the complete absence of all trace of the calcified placoid plates which are so characteristic of the Elasmobranchii.

From Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 8 "Cube" to "Daguerre, Louis" by Various

Placoid, plak′oid, adj. plate-like.—Placoid fishes, an order of fishes having placoid scales, irregular plates of hard bone, not imbricated, but placed near together in the skin.

From Chambers's Twentieth Century Dictionary (part 3 of 4: N-R) by Various

The remains of fish are as yet confined to the upper part of the Silurian series; but some of these belong to placoid fish, which occupy a high grade in the scale of organization.

From Principles of Geology or, The Modern Changes of the Earth and its Inhabitants Considered as Illustrative of Geology by Lyell, Charles, Sir