placoid adjective & noun. ['plakɔɪd] M19.
[from Greek plak-, plax flat plate, tablet + -OID.]
Zoology.
A. adjective.
1. Designating a toothlike fish-scale of dentine and enamel with a flat base, as forming the dermal armour of cartilaginous fishes. M19.

2. Having placoid scales. Formerly spec., of or designating an order of cartilaginous fishes ('Placoidei') including sharks and rays. M19.
b. noun. A placoid fish. M19.

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