While swimming one morning across Coogee Bay in New South Wales, we came across thousands of these strange creatures (see photo) floating at depths down to about 2 metres.

They were hard but also flexible, with water inside and a small hole at one end. Their length varied from about 3 to 30 centimetres and their walls were between 2 and 5 millimetres thick. Their skin was marked with many small protrusions, the size of which varied from one creature to another. Unlike jellyfish they appeared to be completely harmless.

No one I've spoken to from the area has ever come across anything like this. So what were they and why were they there?

Philippe Wilmotte, Maroubra, New South Wales, Australia