Barnacle (Family Balanidae)
Barnacles are NOT clams or even snails. They are more similar to crabs and shrimps. A living barnacle has a door over the opening in its shell. A dead one has a gaping hole. Other animals may shelter in the empty shell.
G1: Star barnacle
Scientific name :Chthamalus sp.
G2: Acorn barnacle
Scientific name : Balanus sp.