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1. Platelike.
a. Relating to or being a kind of fish scale that is a toothlike plate with a protruding spine, characteristic of sharks, skates, and rays.
b. Having placoid scales.

[Greek plax, plak-, flat stone, plate; see plāk- in Indo-European roots + -oid.]


1. (Biology) platelike or flattened
2. (Zoology) (of the scales of sharks and other elasmobranchs) toothlike; composed of dentine with an enamel tip and basal pulp cavity
[C19: from Greek plac-, plax flat]


(ˈplæk ɔɪd)

platelike, as the scales or dermal investments of sharks.
[1835–45; < Greek plak- (s. of pláx) something flat, tablet]
ThesaurusAntonymsRelated WordsSynonymsLegend:
Adj.1.placoid - as the hard flattened scales of e.g. sharks
planar, two-dimensional - involving two dimensions
References in periodicals archive ?
These placoid scales have a drop-like, inclined, elongate crown, well-developed neck and small base with concave basal surface (Fig.
Metastases are typically placoid shaped with an undulating surface and show medium to high blood flow velocity.
Figure abbreviations: ac--acrotergite; as--antecostal suture (ridge); br--transverse row of placoid sensilla on epipharynx; c--claw; cs--campaniform sensillum; dst--distal epipharyengal sensilla; dmr--dorsomesal row of setae on lacinia; er--epipharyngeal rods; f--femur; gl--galea; l--lacinia; lp--labial palp(i); mp--mesal pair of labro--epipharyngeal setae; msr--mesal row of setae on lacinia; mxp--maxillary palp(i); p2--2nd pair of labro-epipharyngeal setae; pr--pretarsus; pls--placoid sensilla; prst--prostheca; s--sensorium (accessory sensory papillae); sbp--subproximal epipharyngeal sensilla; st--stipes; t--tibia; tr--trochanter.
The disease is characterized by infectious etiology and overlapping clinical features in an intermediary form of acute posterior multifocal placoid pigment epitheliopathy and serpiginous choroiditis.
Acute, posterior, multifocal, placoid, pigment epitheliopathy and Lyme disease.
Shark skins bear thousands of rigid denticles, or placoid scales, comprised of hard materials, such as dentin and enamel, which are high in strength and stiffness (Raschi and Tabit, 1992).
Raschi W Tabit C (1992) Functional aspects of placoid scales: a review and update.
Secondly we assign isolated placoid scales from synchronous levels of two stratigraphical sections (Middle Triassic) of the Iberian Chain (Spain), to these "functional" morphologies.
Syphilitic chorioretinitis presents as a vitritis associated with bilateral, large, solitary, placoid, pale yellow subretinal lesions with central fading and stippled retinal pigment epithelial (RPE) hyperpigmentation.
Syphilitic posterior uveitis may present as multifocal chorioretinitis, acute posterior placoid chorioretinitis4, neuroretinitis and retinal vasculitis.