Examining coastal specimens under a magnifying loupe reveals wonderful adaptations:

Shark skin dermal denticles under magnification
📷 Shark skin dermal denticles under magnification

Shark Skin: "Tiny Skin Teeth"

Even though dermal denticles are similar to scales, they are really modified teeth covered with hard enamel. Like our teeth, they have an inner core of pulp made up of connective tissues, blood vessels and nerves, covered by a layer of dentine and finally coated with enamel-like vitrodentine. Dermal denticles protect sharks and rays from skin damage and parasites, in addition to dramatically reducing water turbulence and improving fluid dynamics.

Aristotle's Lantern: Sea Urchin Mouth

The Cape sea urchin's mouth is centred on the lower side of the body and is surrounded by a whorl of gills. A complex jaw and tooth apparatus in the mouth, known as Aristotle's lantern, is used to fragment marine algae covering the rocks below the low tide zone or in rock pools.