Even though they're very small jellyfish are poisonous and they have long tentacles

Even baby jellyfish, the size of a pencil eraser, have the ability to sting. Larval jellyfish, ephyrae, look like tiny flowers pulsating in the sea. As they grow, they become umbrella-shaped with a bell at the top and descending tentacles around the margin. The largest species of jellyfish, the lion's mane, has tentacles that can extend more than 100 feet, longer than a blue whale. These tentacles contain most of the stinging cells, although some species have them on their bells, too.