Words...

My zoology guys are about to tackle the Phylum Cnidaria. It's tough to get excited about the poriferans, but when you leave the sponges behind and move on to the jellyfish and their kin, things can ratchet up a little. And there's the added benefit of some goodies for the literature/philosophy guys too.

One of the things I love about biology is the degree to which it draws upon other disciplines for its terminology and its descriptions. I'm sure that's true to some extent in all fields - psychiatry has it's Oedipus complex and computer guys have their trojan horses. Still, I think biology makes greater use of literary allusions than the rest of them put together. I mean, we use a dead language just to name our organisms. From the Red Queen Hypothesis to the Ghost of Competition Past, there's plenty of opportunities to prove to the crowd that, yes, I read that book.

We lean on the Greeks a lot, and the cnidarians are a prime example. There's Hydra, the little freshwater polyp that draws its name from the nine-headed sea serpent of Greek mythology. And then there's the medusa, the free-swimming, sexually reproducing stage found in most of the cnidarian classes. They're named, of course, for one of the great villians of all time, the gorgon with serpent hair, so hideous that men turned to stone when they gazed upon her. Medusa was beheaded by Perseus, who later would use her still potent head as a weapon. Here she is, as envisioned by the great Harry Harryhausen in Clash of the Titans...

The references to creatures like Hydra and Medusa in the cnidarians are a tribute to their most characteristic feature. All cnidarians possess cells known as cnidocytes, which contain specialized organelles called cnidae. There are a variety of cnidae, but the ones that the phylum are known for are the stinging and food-gathering organelles known as nematocysts. Within certain cnidocytes are capsules which contain coiled, hollow threads and have a hairlike triggering mechanism, a cnidocil, on their external surface. When the cnidocil is stimulated, on contact with a potential prey item or an unfortunate swimmer, the nematocyst penetrates the object and the thread is thrust into it. This is one of the most rapid movements in the animal kingdom, taking place in a matter of microseconds. The toxins contained in the nematocyst are potent - some of the most potent we'll see in the animal kingdom. But that's a story for another day. It's late.