I found a marine version of a four-leaf clover on the beach yesterday, a Moon Jelly (Aurelia aurita). While this is not a traditional symbol of good luck the pretty pink loops look enough like a clover to me. Though perhaps this is an entirely different kind of luck as the loops are actually part of the reproductive system (wink, wink).
A recent study found that the swarms of Moon Jellies we find beached are actually correlated to the lunar cycle. The masses typically peak a week after a full moon, though no explanation was provided. These brainless blobs have been undulating around the world’s oceans for over 500 million years. Clearly, they are tough little survivors.