Wednesday, December 17, 2008

Low Tide: Starfish

A friend and I went down to the beach late the other night for one of the big low tides of the season. Fortunately her headlamp was strong, because mine was in real need of a battery change - I kept forgetting I even had it turned on because it didn't make much of a difference unless I was holding something a few inches from my face.

We saw quite a bit of cool and pretty things. I may post one or two more later on. A friend suggested this intertidal website for identification purposes. I'm not convinced that what I have pictures of are necessarily the same exact species (and I think some of the species I took pictures of are not on that website), but it seems like a pretty cool resource.

One thing I notice about these starfish is that they have a larger white spot just off center. If I had only seen one of these starfish I probably would have assumed that it was just a random spot, but it seems to be on all of this sort of starfish. I wonder what it is?


Kitty said...

Nice photo. Don't know why I never think to go tide pooling in the winter, thanks for the idea.
The white spot is called a adreporite. It is the filter/entrance to the water vascular system.

Jonathan said...

Thanks, Kitty. It's nice to have biologist friends :).

From what I could find I think you meant to have an 'm' in front for madredporite.

Do you know how starfish manage to reproduce by fragmentation? From what I've read/heard the legs can produce another starfish if they contain part of the central disk, but what if they don't have the madreporite, or stomach, or etc.? How do they manage until they build new ones?

Kitty said...

I never could type, yes, I lost the "m" somewhere.
I asked a friend who specializes in invertebrates because I didn't really have a very good answer to your question. He confirmed that they can regenerate with even the tiniest bit of central disk, but don't seem to require an intact vascular (or any other) system. He does wonder how often regeneration happens from such extreme losses. He said that even a 1/2" piece of leg can move around. I'm thinking that the vascular system must seal itself off somehow. Echinoderms do have freely circulating immune cells that probably are important in wound repair and regeneration.