CRASPEDACUSTA SOWERBYI

Say what?  Craspedacusta sowerbyi is our own little freshwater jellyfish complete with a medusa stage!  Okay, we need to talk about jellyfish before we can continue with this story.  Jellyfish are not made of jelly nor are they fish.  I’m pretty sure you already knew that, but I needed to make sure (and I think that is funny). 

These are animals have three body layers.  The outer layer is the epidermis.  The most interior layer is the gastrodermis (forming their gastrovascular cavity – ok – digestive system).  Then they have the middle “jelly filling”.  They also have the unique feature of cnidae (aka nematocytes) which are microscopic harpoons that they use as anti-predator defenses and to subdue their own prey.  The cnidae are so unique that we put all animals with them into a group called the “Cnidarians” which means “bearer of cnidae”. 

So, what cnidarians do you know?  Well, if you saw “Finding Nemo” you saw a bunch!  The sea anemone house that Martin and Nemo lived in was a cnidarian.  The coral reef they lived on was a colony of cnidarians.  The jellyfish that they bounced on were jellyfish. 

Cnidarians have a basic life cycle where the swimming adults (medusa stage) release their eggs or sperm into the water and hope for the best.  If an egg is fertilized, it will start to develop into a little larva (planula stage) that can swim and find a good spot to live.  It will then settle down and start to develop into a little blob-like tree (polyp stage).  The polyp will stay put.  It can make clones of itself or it can make medusas that can swim around and reproduce sexually.  Different types of cnidarians have variations on this life cycle. 

Most of the varieties of cnidarians are marine.  So, it might be surprising to note that there are freshwater jellyfish too.  Here in the Ozarks, right NOW (early September) you may find a Craspedacusta sowerbyi medusa bloom in a lake or pond.  Look for penny-sized jellyfish.  Don’t worry about the cnidae.  The stings are enough to paralyze their prey (smaller animals) but not enough to penetrate our skin.

This is the sad part.  While we have Craspedacusta sowerbyi here in the Ozarks, it really isn’t OURS.  It is an exotic invasive species indigenous to the Yangtze River valley in China.  It was first recorded in the U.S. in 1880 and may have been accidentally introduced through ornamental aquatic plants.  It now occurs in 44 states.  Including ours.  Exotic means it isn’t from these parts.  Invasive means it spreads like wildfire.  Often exotic invasive species spell trouble.  They out compete our native organisms (those from here) and cause them to decline.  The effect of Craspedacusta sowerbyi isn’t clear.  Perhaps because it has been with us for so long.  At least the crayfish eat them!