by Stacy Hackner

“Sharks have eyes and mouths, and we hear all about their ability to smell blood. How do they hear?” Once again, a visitor had me stumped. Despite their having only tiny holes for external ears, sharks actually have very acute hearing, I later learned. Like in humans and other mammals, the shark’s inner ear has tiny hairs called stereocilia that vibrate, which is interpreted by the brain as sound. The stereocilia are arranged in three fluid-filled tubes, allowing the shark to hear in multiple directions. (These tubes are also responsible for the shark’s sense of balance.)

Sharks can hear low frequencies much better than humans, ranging from 10-800 Hertz (for reference, humans can hear between 25-16,000 Hertz), and can hear prey up to 800 feet away. In combination with their formidable sense of smell and speed, this makes them fearsome predators. (The big ones, at least.)

The angel shark, with ears visible just behind the eyes.
Courtesy Grant Museum.

Sources:

Shark Trust

Sharks Interactive 

By Ruth Blackburn

The aptly named brain coral is a dome-shaped member of the family Faviidae which has distinct sinuous valleys (that’s the wibbly ridgey bits that look like the surface of a brain).

So why the dome shape?  This is largely driven by the position of the coral within the reef: brain coral is found in shallow parts of reef at a depth of about 1-15 metres. At this depth there is substantial wave action, which corals with a compact spheroid shape are much more resilient to than those with thin antler-like projections.

Brain coral from the
Grant Museum collection.

The sinuous valleys on the surface of the brain coral can also be explained.  These mark the areas in which polyps – soft bodied marine creatures – are most densely found.  Polyps are able to secrete calcium carbonate (just like the scale that builds up in your kettle) to form a hard and protective exoskeleton that it can live in: this exoskeleton is what you actually see when you visit the Grant Museum.