The Bug Geek

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Tag Archives: Cnidaria

Overheard in the teaching lab (or, “Disenchanted student PWND”)

Photo from Wikipedia


  Last week my students studied, among other things, Cnidarians.  One of two radiate phyla (the other is the Ctenophora), this group of aquatic/marine-dwelling critters includes anemones*, corals, hydrozoans and jellyfish.  Among various pickled and slide-mounted specimens I had out for the students to examine, one microscope held a slide of jellyfish nematocysts. A student bent over the bench, peeked through the eyepieces at the little purple-stained squiggles highlighted below the lenses, and quipped, “Huh.  Well THAT’s nothing remarkable.” 

 O NOES!!!  Clearly this student needed some edumacating about the extreme coolness of these so-called “unremarkable” purple squiggles!   I called the entire class to attention, yanked down the screen for the projector, typed furiously on my laptop and pulled up YouTube.  

 “THIS”, I said.  “THIS is what you’re looking at on that slide.”   


 “Unremarkable, my ass!”, I said.  “That jellyfish is a freaking NINJA!”   POW!  ZAP!  PWND!    

The class was suitably impressed, including Mr. “not remarkable”.   Harumph.    

Nematocysts, housed in specialized cells called cnidocytes, are the stingy bits of the jellyfish…specially modified organelles that lie coiled in wait, like a den full of vipers, waiting to be triggered into deadly action by unsuspecting prey or a naïve predator wannabe.   The firing of nematocysts is one of the fastest known cellular reactions:  an acceleration of  up to 5,410,000 g.   Consider this: a dragster can accelerate from zero to 160 km/h in 0.86 seconds, creating an acceleration of 5.3 g.   Yup, only 5.3.  I think it’s safe to say that the jellyfish wins this race hands-down.
Using videos or excellent photographic images to highlight interesting features and show students “live” animals (versus simply having them examine stained/mounted/sectioned pieces of them) is proving to be an effective tool in my classroom.  Looking at an amoeba** on a slide (“Um, is that the amoeba?”  “No, that’s lint, keep looking.”) is useful, but complementing THAT experience with one of  actually watching one extend its pseudopods as it locomotes and engulfs food particles…in the absence of live specimens, it’s a more memorable study of the animal overall.     

Having used videos in two classes now, with very positive feedback…I think it’s something I’ll be employing regularly.   


 * does anyone else find this word to be a bastardly mouthful, determined to be mispronounced at every turn?  I have to pro.nounce thoughtfully or else it comes out as “anENoME” 

 ** amEba or amOEba?  I’m used to the latter, but everything I read these days uses the former.  When did we lose the “O”?  I liked that “O”.

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