Sharks possess a unique and complex skin covering that sets them apart from most other fish. Unlike traditional fish scales or smooth skin, a shark’s outer layer consists of structures called dermal denticles. This specialized integument plays a significant role in their survival and efficiency in marine environments.
Beyond Scales: What Sharks Really Have
Sharks do not have traditional fish scales or smooth skin. Instead, their bodies are covered by structures known as dermal denticles. The term “dermal denticle” literally translates to “skin tooth.” These structures give shark skin its distinctive, rough texture, often compared to sandpaper. Unlike the scales of bony fish, dermal denticles are composed of materials similar to those found in teeth.
The Unique Structure of Dermal Denticles
Each dermal denticle features a flat base embedded within the shark’s skin, a neck, and a pointed crown. These crowns are made of dentin and are covered by an enamel-like substance, mirroring the composition of teeth. The denticles are arranged in an overlapping pattern, pointing backward towards the tail. This arrangement contributes to the rough, abrasive feel when stroking a shark from tail to head, while feeling relatively smooth when stroked from head to tail. The size and shape of these denticles vary significantly depending on the shark species and their location on the body.
How Dermal Denticles Benefit Sharks
Dermal denticles provide sharks with several functional advantages. Their unique shape and backward-pointing arrangement improve hydrodynamics, reducing drag and turbulence as the shark moves through water. This design allows sharks to swim more efficiently, much like the dimples on a golf ball reduce drag. The denticles create tiny vortices that form a buffer layer, preventing turbulent wakes and allowing for faster movement.
These denticles also act as protective armor, offering defense against predators, injuries from prey, and environmental abrasions. The rough texture deters parasites, algae, and barnacles from attaching to the shark’s body. Additionally, dermal denticles may possess sensory capabilities, aiding the shark in detecting water movements or prey.
Dermal Denticles Versus Fish Scales
Dermal denticles differ significantly from the scales found on most bony fish. A primary distinction lies in their origin: dermal denticles develop from the dermis (inner skin layer), similar to how teeth develop. In contrast, bony fish scales originate from the epidermis (outer skin layer).
Another key difference is how they grow: dermal denticles do not increase in size as the shark grows; instead, new ones are added to cover the expanding body surface, much like new teeth replace old ones. Fish scales, however, grow with the fish, often showing growth rings. Finally, their composition also sets them apart: dermal denticles are tooth-like, made of dentin and an enamel-like substance, while typical fish scales are bone-like.