Cryptoplax sp.

Comment from expert, Richard Willan: This is chiton (coat-of-mail animal), a mollusc in which there are 8 shell plates dorsally over the back of the animal. In the family Cryptoplacidae these plates are reduced in size and mostly covered by the mantle, so only their summits are visible as a row of little hard triangles along the mid-line of the back. Species of Cryptoplax are generally nocturnal.