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

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Example Sentences

See Examples For:

placoid

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

But one of the most remarkable weapons of the period was the sting of the Pleuracanthus, another great placoid of the age of gigantic fishes.

From The Testimony of the Rocks or, Geology in Its Bearings on the Two Theologies, Natural and Revealed by Hugh Miller

Many years before, several observers—J. Müller, Williamson, and Steenstrup—had been struck with the resemblance existing between the placoid scales and the teeth of Elasmobranch fishes.

From Form and Function A Contribution to the History of Animal Morphology by E. S. (Edward Stuart) Russell

Besides the teeth there perhaps remain relics of the placoid scales in the anatomy of the higher vertebrata, in the membrane bones.

From Text Book of Biology, Part 1: Vertebrata by H. G. (Herbert George) Wells

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