Placoid

The new species is highly adapted to hypogean life with very obvious troglobiomorphic features: unpigmented cuticle, an extraordinary lengthening of thorax and appendixes, multiplication of antennomeres and supernumerary placoid sensilla, not just in the apical antennomere but also in the preceding antennomeres. ❋ Unknown (2007)

The placoid scales on a shark are a phalanx of precise dermal teeth. ❋ Alexander Theroux (2007)

Finally, with respect to the ‘Vertebrata’, the same law holds good: certain types, such as those of the ganoid and placoid fishes, having persisted from the palaeozoic epoch to the present time without a greater amount of deviation from the normal standard than that which is seen within the limits of the group as it now exists. ❋ Unknown (2007)

Hertwig followed up this clue, and came to the conclusion not only that placoid scales and teeth were strictly homologous, but also that all membrane bones were derived phylogenetically from ossifications present in the skin or in the mucous membrane of the mouth, just as cartilage bones were derived from the cartilaginous skeletons of the primitive Vertebrates. ❋ Unknown (N/A)

Steenstrup -- had been struck with the resemblance existing between the placoid scales and the teeth of Elasmobranch fishes. ❋ Unknown (N/A)

How placoid scales may have given rise to these structures will be understood by considering such a bone as the vomer of the frog. ❋ Unknown (1906)

The first Vertebrata to appear in the fossil history of the world are fishes; fish spines and placoid scales ❋ Unknown (1906)

This bone lies on the roof of the frog's mouth, and bears a number of denticles, and altogether there is a very strong resemblance in it to a number of placoid scales the bony bases of which have become confluent. ❋ Unknown (1906)

The skin of the dog-fish is closely set with pointed tooth-like scales, the placoid scales, and these are continued over the lips into the mouth as teeth. ❋ Unknown (1906)

These facts seem to point to stages in the fusion of placoid bases, and their withdrawal from the surface to become incorporated with the cranial apparatus as membrane bones, a process entirely completed in the mammalian type. ❋ Unknown (1906)

Besides the teeth there perhaps remain relics of the placoid scales in the anatomy of the higher vertebrata, in the membrane bones. ❋ Unknown (1906)

It is the same with the cutaneous teeth or placoid scales of the Selachii. ❋ Ernst Heinrich Philipp August Haeckel (1876)

Finally, with respect to the 'Vertebrata', the same law holds good: certain types, such as those of the ganoid and placoid fishes, having persisted from the palaeozoic epoch to the present time without a greater amount of deviation from the normal standard than that which is seen within the limits of the group as it now exists. ❋ Thomas Henry Huxley (1860)

Old Red Sandstone, -- some were remarkable for the strangeness of their forms, and some for constituting links of connection which no longer exist in nature, between the ganoid and placoid orders. ❋ Hugh Miller (1829)

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. ❋ Hugh Miller (1829)

The dorsal spine of its contemporary, the Gyracanthus, a great placoid, much exceeded in size that of any existing fish: it was a mighty spear head, ornately carved like that of a New Zealand chief, but in a style that, when he first saw a specimen in my collection, greatly excited the admiration of Mr. Ruskin. ❋ Hugh Miller (1829)

Brezin A, Massin-Korobelnik P, Boudin M, Gaudric A, et al. Acute posterior multifocal placoid pigment epitheliopathy after hepatitis B vaccine. ❋ Unknown (2009)

Dogfish Shark Placoid Scales - The bodies of dogfishes, like all sharks, are externally lined with placoid scales, also known as dermal denticles.