The extraordinary animals living on their heads are Barnacles.
You might have noticed barnacles encrusting large rocks at low tide and mistaken for some kind of Mollusc. Earlier called as Mollusc they were actually found to be a type of Crustaceans after noticing larvae hatching from eggs that had several features common with crustaceans. They belong to the same group to which crabs, lobsters etc. belong.
The larva swims around feeding and growing and then changing into a shelled form and then chooses a place on a surface to settle its head first and quickly encloses itself in a shell made of plates.
When the tide exposes the barnacle, the plates stay closed to prevent loss of water from the animal and when the tide returns the top shell opens and feathery feet are pushed out to comb water for suspended food particles.
Barnacles vary in diameter from .25 of an inch to 1 foot found in North America.
These small creatures actually caused ships to slow down by settling on their bottoms and ships had to paint the surfaces to prevent larvae from settling.
Being exclusive marine in nature they tend to live in shallow and tidal waters.
Barnacles are not generally harmful but turtles get affected if excess barnacles stick to its surface.
Believe it or not! Barnacles are edible and delicious and can be harvested like any other seafood. Not many countries have consumption of these creatures but Spain, Portugal, Morocco and Canada top the list in terms of harvesting and eating barnacles.