Jellies at Shedd

We're in the middle of getting 6-8 inches of snow here in Chicago.  We've been putting off going to the museums until the winter weather really kicked in, and today was the perfect day to have an indoor adventure.  We spent a couple of hours at Shedd Aquarium, and we could have spent several more there.  My favorite exhibit was of the animals formerly known as jellyfish, currently known as jellies since they really don't have anything to do with fish other than the fact that they live in water.  I could watch them for hours - they are mesmerizing and fascinating.  Another museum-goer called them living lava lamps.

Northeast Pacific Sea Nettle, Chrysaora fruscescens

 I've written about jellies before, so I'll take a different approach here.  I'd like to point out some interesting anatomical structures and explain a little bit of their life cycle.  Let's start with anatomy.

The jellies above are swimming upside down.  The main body is called the bell.  There are two types of structures that trail behind the bell: tentacles and oral arms.  Tentacles are darker in the Pacific Sea Nettle, and they extend off of the edge of the bell.  Oral arms are usually whitish, four in number, and extend from the center of the bell.  Both appendages are covered in microscopic stingers.  The tentacles are for initial stinging of food and defense.  The oral arms are for more stinging and for moving food toward the center of the bell for digestion.

Jellies have only one orifice on their bodies, which has to serve for the in and out orifice of the digestive, reproductive and respiratory systems.  Food goes in, gets dissolved, is carried out through the rest of the body, and whatever isn't digestible is 'spit' back out.  Reproductive organs, visible as the four ring-shaped white structures in the moon jellies below, connect to the single orifice.  Males release sperm into the ocean water.  Females can release eggs into the ocean water, hopefully to find a sperm somewhere, or more commonly, they take in sperm, allow fertilization, and even allow development of the next generation inside their body cavities. 

Moon Jelly, Aurelia aurita

Jellies have a ring of muscle one-cell-thick around the edge of the bell that they can contract and relax to move.  Also around the edge of the bell, it is common for jellies to have light-detecting tissue for knowing when to swim up to the surface of the ocean.

Good view of the two types of appendages attached under the bell.

The jelly life cycle is pretty head-scratching.  The pictures on this page show all adult forms, but they have juvenile forms that look completely different - like butterflies and caterpillars look different.  Fertilized jelly eggs grow into larvae called planulae.  Planulae are almost microscopic and swim free in the ocean.  Some planulae can sting, and those invisible stings that sometimes get trapped inside your bathing suit could be planulae or they could be broken-off adult stingers.  Planulae swim to a hard surface, like a pebble or a rock, and they stick and grow into a polyp.  A polyp is a cup-shaped, usually transparent animal with tentacles in a ring around the top of the cup.  The bottom of the cup is stuck fast to a surface.  Polyps can grow mini-polyps off the side of themselves, which can fall off and become independent organisms (this is asexual reproduction by fragmentation).  Eventually, polyps grow a beret-like structure, let go of their substrate, and become an adult medusa to roam the ocean, sting at will, and reproduce the next generation.  Here is a nice diagram of the jellyfish life cycle.

Flower Hat Jelly, Olindias sp.

I'll end with a picture of an extremely strange jelly, the flower hat jelly.  It keeps its tentacles tucked up underneath its bell, and it extends them quickly when they are needed.  It is a benthic species, spending most of its time on the sea floor.  Those tentacles that extend off the top of the bell are mysterious, but I do know they are called exumbrella tentacles.  They might be lures to attract prey, or they could be stinging tentacles for self-defense.  If you are searching for a creature to study to make a name for yourself as a scientist, this might be a good subject, because little is known about it.

If you'll be in Chicago sometime in the next year, you're invited to come with me to the Shedd Aquarium - we have a membership!

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.