Not the most complicated of creatures, jellyfish. And not the most complicated of words either.

Jelly + fish = jellyfish. Easy. I heard the word during a song this evening, and was struck by its simplicity. But of course I had the feeling that there’d be something interesting, linguistically, about jellyfish.

And so I found myself on the Wikipedia entry for jellyfish. And that was just the beginning…

The first word that jumped out at me was medusa-phase!! According to Wikipedia, jellyfish are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa. If you have even a passing knowledge of classical mythology, you can probably imagine what medusa-phase refers to.

Medusa of course was the famous Gorgon encountered by Perseus, with venomous snakes instead of hair. The medusa phase of an animal typically involves an umbrella-shaped structure with stinging tentacles around the edge, so there’s something of a resemblance. Medusozoa are distinguised from other members of the phylum Cnidaria by this stage featuring in their development.

The precise term for a specific subgroup of animals sharing common descent, like Medusozoa, is clade. Other more famous clades include rodents, insects, and dinosaurs. Clades can have subclades within them, like mice, or ants. Clade comes from the Greek klados, meaning branch, as each represents a branch on the figurative tree of life.

All very interesting so far, but what I was most pleased to learn is that like bugs, there are jellyfish, and then there are true jellyfish!

You’re probably dying to know right now what exactly makes members of the class Scyphozoa true jellyfish. It’s not that other jellyfish aren’t jellyfish, but rather they’re composed of different polyps working together, while a true jellyfish is a single organism composed of two layers. And don’t worry if you feel you’ve been lied to your whole life about what are and aren’t jellyfish: most jellyfish that you see and that look like classical jellyfish are in fact member of Scyphozoa.

But the most important question of all is: is a jellyfish, true or otherwise, a fish? Well that’s such a complex question, it’ll have to wait till tomorrow!