Yesterday I collected three very small Pycnopodia helianthoides stars. When I brought them back to the marine lab I decided to photograph them because with stars this small I could easily distinguish between the original five arms and the new ones:
These guys began their post-larval life with the typical five arms you'd expect from an asteroid. At this stage they are pretty conspicuous because they are the largest arms. The other arms arise in the inter-radial regions between arms. For years now I've been wanting to watch juvenile Pycnopodia stars growing their extra arms, and it looks like I finally have my chance. I noted that these stars are all about the same size, but don't have the same number of arms. It would be interesting to see if the rate of arm appearance and growth is related to how much food the stars have. Hmmm, that sounds like a study I should do.
And then one of the stars started running. And I mean running. Watch:
You might wonder how in the heck they can run so fast, and it's a valid question. We can actually examine the animal's scientific name to get an answer. "Pycnopodia" means "dense foot" and "helianthoides" means "sunflower-like." So these guys have a lot of tube feet, and they use them to run and feed. Imagine how fast we could run if we had more than two feet and could co-ordinate them this well:
So, when these guys (gals?) grow up, they'll be at least half a meter in diameter with 20-24 arms. With all those tube feet, they'll be Speedy Gonzales! In fact, they will be the terror of the intertidal--big, fast, and voracious. Anything that can't get out of their way will be eaten.
We air-breathing land mammals should be grateful that echinoderms never managed to get out of the sea. Can you imagine this monster chasing you down a dark alley, or climbing through your bedroom window?