Unknown specie found on howksbay beach Karachi, Pakistan

Yesterday I went to howksbay beach with my friend and found this specie attached with a rock we were looking for sea shell and found this. There are two parts of it one is brown and other one is white both look like painting brush when we thrown stone on it its both parts went to those holes or pipe shaped things look like made of rubber when we touched it. I don't know what is this if anyone know about this please let me know.