This is a Portuguese Man O’ War, a hydrozoan that is often called a jellyfish, and more importantly, can sting just like one. Their venom is incrediblypotent, and both severed tentacles and dead specimens can inflict painful stings. In the bestcase scenario, their sting will cause excruciating pain and long, open welts for a few days. In the worst case scenario, their sting can cause fever and shock, or allergic reactions, which have been known to result in death. You should neverdirectlyhandle a man o’ war, especially not with bare hands in a cup like this.
If you are stung by a man o’ war, immediately seek medical attention. Common “household remedies” like vinegar can actually worsen stings, and there is no way to tell how someone will react to a sting.