Description: I was taking microscope pictures of a sea slug the other day (Elysia chlorotica), and I was having a hard time because the slug kept leaving the center of the bottom and climbing the walls of the bowl (a flat-bottomed bowl about 8 cm in diameter). No matter how many times I put it in the center, it would always find the shortest route to the edge and climb the wall. I seem to remember I've had this problem with other sea slugs before. So, the question is, why do they do that? What makes the sides of the bowl so appealing? I know it's not the microscope lights, because the slug didn't always crawl up the same part of the bowl.
Page creator's name: Yasmin von Dassow
Page creator's contact info: yasmin.vondassow@duke.edu
behavior biology mollusk sea-slug
Created: 24 Mar 2014 01:53
Updated: 29 Mar 2014 19:16
Comments: 04 Apr 2014 15:09
#Comments: 2
Nice picture! I think that the term for this sort of behavior is thigmotaxis. I've found that other mollusks such as chitons and limpets love to wedge themselves in corners, perhaps because they're harder to dislodge from corners than from flat surfaces.
I'm not sure it's the topography they're responding to. I thought I might be able to trap them somewhere more convenient for filming by putting a small dish under the water surface (so there wouldn't be a meniscus, but it would have an edge to crawl around) but it just crawled right up over the lip and onward.
The most obvious explanation is that in a circular container they'd crawl approximately straight until they hit a boundary (the water surface) and then crawl as straight as they could along it, thereby circling the water's edge. However, this sea slug (and it seems like others) seemed to turn towards the shortest path to the wall, wherever we put it (obviously, there's likely to be observer bias).
One possibility may be that we tend to push it from the edge towards the center, so if it turns towards the side on which it was pushed, it would be turning directly for the wall. (I guess this would be a slightly different form of thigmotaxis). Maybe next time we should try pushing it past the center to the far edge: if it turns towards the side on which it was pushed it would then take the long way across the dish.
Assuming they do turn towards the pushed-on side, any idea why they'd do so?