I betcha you guys didn't know that starfish left FOOTPRINTS did ya?? I don't just mean impressions on the sand..I mean, put a starfish on a smooth surface, like glass or rock and it leaves you one of these...
Hasn't the model always been that starfish tube feet work like suction cups (such as here) ???? Why would they leave footprints on a smooth surface if they work like suction cups??
Image by Symbiotics
THAT is a good question.
To answer it, I consulted the works of Patrick Flammang and his research lab at the University of Mons in Belgium. One of many papers addressing the biology of tube feet is utilized here (written by Elise Hennebert and others in Flammang's lab)
There is an important lesson to be learned here. This field of study started largely as an academic pursuit, to learn about the mechanisms used by these animals to survive in their habitat but may soon lead to something with many practical applications..
See this article awhile back about how Gecko adhesion has led to new types of adhesives! Adhesives that work under water would presumably have a multitude of uses..
There is a special layer called the "fuzzy coat" (shown below in red) which is present on the surface of the disk epidermis making contact with the bottom.
|Echinoblog Art Dept.- Note that "Smuck" is not known to be a true starfish tube foot noise!|
|Echinoblog Art Dept. Did you know that ! can be used to make everything more exciting?!!|
|Echinoblog Art Dept. Coloring is fun!|
|fig. 1B from Hennebert et al. 2008|
This leaves the "fluffy layer" and the "bulked" material behind...
|Figure 2C from Hennebert et al.|
5. Footprint And the wet parts of the "fluffy layer" dry out leaving the "bulked" material aka the starfish (or whatever) footprint..
Here is what that part which is left behind looks like in 3D via Transmission and Atomic Force Microscopy
|Fig. 3 from Hennebert et al.|
And here is an image of the tube foot "foot print" as seen directly off a piece of glass..
What about that classic paradigm about suckers on sea stars and other echinoderm tube feet basically being suction cups???
Bear in mind that this doesn't even necessarily end with this one tube foot type. There are at least two other forms of tube feet and exploring the various mechanisms at play could be fruitful indeed...
In addition to the lab run by Patrick Flammang at the University of Mons, this lab in the UK (shown in this video) has also undertaken research into this area to understand the nature of tube foot adhesives...
UPDATE: To see the follow up to this story and to see how "echinoderms don't suck" go here!