Jellyfish, corals and sea anemones are all members of Phylum Cnidaria (silent C), which means they are radially symmetrical and have venomous stinging structures. Comb jellies are members of Phylum Ctenophora (also silent C), which means they are also radially symmetrical but have comb-like cilia and are carnivorous.
I pretty much assumed that everything gelatinous and floaty in the ocean would leave painful welts that would become infected and lead to a costly doctor's appointment. Wrong! Many jellyfish have such weak stings that humans can't be punctured. In fact, the ones I most often see in Florida are mostly harmless to all humans except the most thin-skinned. The cannonball jellyfish, can apparently cause heart problems if you rub your eyes on its short tentacles, but you can pick it up or brush into it with no problem. The moon jellyfish, according to the guide to Florida jellyfish that I read while on our honeymoon, do not sting humans. I did not test this myself, but I did manage to convince my husband to pick one up, and it did not sting him. Subsequent reading about this species reveals considerable difference of opinion about the the moon jellyfish's ability to sting humans, but the most reliable-sounding Internet sources say it can only mildly sting thin skin. I chalk the reports of dire consequences up to general fear and misinformation about jellyfish.
|A swimming (or is that hunting) brown comb jelly.|
|A brown comb jelly temporarily collapsed into a pile of goo in my hand.|
|Brown comb jelly in better light with tree reflection.|
My other major misconception about jellyfish and comb jellies is that they can only stupidly float wherever the current takes them. Again wrong! While they are certainly not strong swimmers, jellyfish and comb jellies can move toward and away from things like light, movement, smells and salinity differences. It's true they don't have brains, but they do have nervous systems to sense the environment and coordinate movements. Some jellyfish even have fairly complicated camera-type eyes! Many jellyfish only have to concentrate on staying upright. Others, like the cannonball jellyfish above, can swim quickly up and down in the water to find food.