placoid
Americanadjective
adjective
-
platelike or flattened
-
(of the scales of sharks and other elasmobranchs) toothlike; composed of dentine with an enamel tip and basal pulp cavity
Etymology
Origin of placoid
1835–45; < Greek plak- (stem of pláx ) something flat, tablet + -oid
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
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
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 Wells, H. G. (Herbert George)
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
As to whether they represent the remnant of a once present system of epidermal scales, which may have preceded the coating of placoid elements in the evolution of the vertebrate, there is no evidence.
From Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 8 "Cube" to "Daguerre, Louis" by Various
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
