Sponge

Thx for the advice.

Sorry, but this branch of marine biology may require the advise of an expert (which I am not), usually samples are needed, spicule shape, density and tissue are studied in detail to differentiate subspecies. Was the body soft or rigid? What is the diameter of a tube and the length of the structure? Better chance to get proper advise from a university... You may try to contact Edwin Cruz-Rivera from The American University in Cairo, he might be able to know someone up to the task.

Thank you for your help. I always thought, it's a sponge, but on the sites I visited I found no advice of any species.

it is a demosponge... I am no specialist but proper identification of porifera may prove tricky.

Some sort of tube sponges :-)