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Sunday, June 21, 2015

Keen on keenae

Not too long ago, Eric wondered why I hadn't posted more pictures of local snails.  I think he was surprised because it was one of the first groups I started studying when I moved to California.  To be honest, I'm not sure what the answer is.  Many of them are small, so perhaps hard to photograph.  But since his observation is true, I'll be trying to share some more snail photographs.

These are Eroded Periwinkles (Littorina keenae) in a narrow crevice in the splash zone (the highest level of the rocky intertidal zone).  They live higher than any other marine gastropod.  They can be out of the water for such long periods of time that some people might consider them semi-terrestrial.

They're called Eroded Periwinkles because their shell erodes as they age.

This is a helpful characteristic when you're trying to identify them, but if you only look at larger, older individuals, you miss out on the wonderful variation and patterning of the juveniles:

As you can see, some are pale, others are dark (mahogany brown?), and they have variable amounts of white.  It's amazing how well these combinations match the surrounding rocks.

Below are two more examples of the pale and dark forms:

Although they blend in well, once you know what to look for, I'm guessing you'll find some Eroded Periwinkles in splash zone crevices during your visits to the coast.


.hbp said...

What causes their shells to erode as such?

Jackie Sones said...

Hmmm...not sure I've read anything about the cause of the erosion of Littorina keenae shells. When I think about it, it seems like it could be related to weathering (e.g., wetting/drying, wave splash, wind, even blowing sand/rock material when it's airborne in high wind conditions)...or perhaps due to biological factors, e.g., algae (or bacteria/fungi) growing on/in their shells. It does seem as though Littorina keenae is more eroded than other snails in this area, so it might have something to with the tidal height at which they occur. Some of the limpets and barnacles also have eroded shells...but it's an interesting topic to explore whether the factors that cause erosion are the same in all of these species, or if some species are more susceptible than others and why!