Under the Magnifying Glass

Shark skin “tiny skin teeth” 
Even though denticles are similar to scales, they are really modified teeth and are covered with a hard enamel.
Like our teeth, they have an inner core of pulp made up of connective tissues, blood vessels, and nerves, which is covered by a layer of dentine a hard calcareous material. This is finally covered by enamel-like vitrodentine, which provides a hard outer casing.
Dermal denticles protects Sharks and Rays skin from damage and parasites in addition to improving their fluid dynamics.
Shark skin dermal denticles
Dermal denticles
Mouth of a sea urchin
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.