Glaucus atlanticus– get yours; don’t be stingy!
This pretty nudibranch packs quite a sting! Derivative work based on photograph by Taro Taylor from Sydney, Australia.
CC-BY-2.0: “This Glaucus atlanticus was washed up on Surfers Paradise Beach in Queensland Australia. It is about 35 mm in length. The species swims upside-down and is accordingly countershaded for that position.” (Wikipedia)