Earthworms and Sea Stars -- cool!

In yesterday's class, we started class by talking about an unbelievable property of some hydras that I hadn't fully known about before -- some scientists think they may be immortal!  No one has found evidence that their cells age and deteriorate the way all other life forms do.  Here is information about an article that you can get for free about a study looking at this, and they found that in four years of study, hydras didn't seem to age or die, and reproduction stayed the same.  They compared hydras with several other species that show the normal pattern of growth, reproduction, then decline in reproduction and then death, and found that hydras don't show evidence of aging and death!

Next we did a lively and entertaining classroom quizshow on planaria and mussel, which we dissected last class.  It was a close game, with the Planarians taking an early lead and the Mussels then trying to catch up.  In the end, it was the Planarians who won, 2 to 1, but everyone did a great job and had fun.  Some facts we reviewed that I didn't mention in my last post included:

• Planaria can live in water or on land.
• They are carnivores and eat living or dead small animals.
• Mussels are bilaterally symmetric (I had been confused about this!)
• They are mostly freshwater animals and have very strong muscles for moving and keeping their shells closed.
• Zebra mussels were originally native to streams of southern Russia, and are now an invasive species in North America, including Wisconsin.

The rest of class was focused on earthworms and sea stars.  For homework, students accessed the online earthworm species database, where you can find out the names of all the earthworm species that have been characterized.  We each looked up how many species of earthworms were named in the year we were born.  Here's what we found:

• My birth year of 1973:  38 species, one of which was Platydrilus simplex
• Year   # of earthworms named  (students' chosen species)
• 1998   32
• 1999   65  (Amynthas sexpectatus, Amynthas binoculatus, Dendrobaena Negevis)
• 2000   389
• 2001   37
• 2002   40  (Cubadrilus barroi)
• 2003   13  (Proandricus lovuus)
• 2004   94
• 2005   34

As we could all see, it's amazing how many species of earthworms there are in the world, and to see that people from all over the world are naming and characterizing new ones all the time!  One fact I found about earthworms is that the Maori people of New Zealand use the word Noke for earthworms that they eat as delicacies.

We dissected earthworms and could see that they are bilaterally symmetric, have lots of organs (including five hearts!), and are hermaphrodites.  They have a digestive tract all down through them, have little spike things on the bottom to help them move, and most of ours had over 100 segments!

Next, we talked about and dissected sea stars.  We learned that sea stars can regenerate arms and saw that several of the sea stars we had appear to have been growing an arm back, because one was smaller than the rest.  Sea stars are radially symmetric, and they have little foot structures on the bottom to help them move.  Their mouth is on the bottom in the middle, and they have a tiny round spot on top that they use to suck water in.  They do not have a backbone and are invertebrates, like all the other animals we've studied so far.  

We have two more invertebrates to study next week, the grasshopper and the crayfish, and then we'll do a big invertebrate review quizshow and move on to a hemichordate (missing link between invertebrates and vertebrates) and then to the chordates (vertebrates).  Very cool stuff!