unknown creature

There were many of these on sandy flats off Bimini at 30-40 ft. They look like a cut-off top of a plastic bottle with a diagonal cut across, so they are not circular. Soft and easily broken. Someone tried to lift this thing on board but it broke into pieces.

We came into contact with this mysterious sea creature, or colony, while sailing the Indian Ocean off the coast of Palau Komodo, Indonesia. We believe this is the responsible party for some nasty stings that forced us out of the water earlier than we wanted. If you know what this is please...