You might be familiar with this creature if you regularly go for a stroll on the beach.
Goose barnacle Lepas sp., a small, fixed, shelled animal often found colonising slippers, bottles and almost any kind of solid objects available in the sea. Despite their appearance, these are in no way related to shellfish, in fact they are crustaceans, close relatives of prawns and crabs. The tentacle-like parts sticking out of the shell are in fact modified "legs", used to catch floating food particles in the water current.
Specimens commonly washing up on beaches are about 2-5cm long. This colony, found and photographed on a buoy in the middle of the Arabian Sea, had individuals up to 10cm long, by far the largest I have seen.
Canon 500D, 100mm Macro USM
Thanks, C&C awaited.