Dangerous Animals Week, Part I

Even farmers go on vacation.  Especially when they get married and go on a honeymoon!  We went to Florida over the weekend, and I took the chance to get to know our gelatinous friends of the sea, the jellyfish and comb jellies!  There are many great mysteries in the ocean, and these critters are some of the least understood - even by Biologists.  I suppose even I have been avoiding them all these years.  I have been so blind.

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. 

Cannonball Jellyfish

Cannonball Jellyfish

Comb jellies most definitely cannot sting.  Reports are unanimous about this, and I tried it out myself.  Below is a brown comb jelly in the water, and below that are two brown comb jellies in my hand.  Comb jellies are shaped rather like a stocking cap with rows of cilia along the long axis.  Those cilia reflect the sunlight beautifully.  Comb jellies can open and close one end of themselves, depending on whether they are eating something or not.  Since comb jellies are transparent, you can see what they have eaten.  Brown comb jellies eat American comb jellies, which are smaller and colorless.  I watched a brown jelly, which had obviously already eaten once already that day, engulf an American jelly in 5 seconds flat.  Once the prey was inside, the brown jelly sealed itself and probably spent the rest of the day digesting and absorbing its two meals.

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.

Of course, many jellyfish can sting in a major way.  The box jellyfish hurt badly, and some found in Australia are deadly.  The man-of-war can put you in the hospital (incidentally, there is a jellyfish called the by-the-wind jellyfish that looks much like a man-of-war but can't sting people).  There are sea wasps, sea nettles, lion's mane jellyfish and more.  I don't recommend learning which are dangerous by trial-and-error.  Here's a good .pdf guide to Florida jellyfish.

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.