placoid

[ plak-oid ]

Phonetic (Standard)IPA

adjective

placoid

/ ˈplækɔɪd /

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

Origin of placoid¹

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

Origin of placoid¹

C19: from Greek plac-, plax flat

The tail is asymmetrical (heterocercal), and numerous placoid scales (dermal denticles) are embedded in the skin.

They pass by quite insensible gradations into normal placoid scales, such as cover the general surface of the body.

In some cases the placoid scales are enlarged to form plates or spines capped or coated with enamel.

The Thornback Skate is covered with prickles (placoid scales).

The teeth of Selachii are fundamentally identical with placoid scales.

April 19, 2024tortuous

[tawr-choo-uhs ]

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