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Sunday, December 6, 2015

"Shield up"

I think it was about 8 years ago when I first saw a Pear Marginella (Granulina margaritula).

This is a very small snail.  Pear Marginellas reach a maximum length of ~2-3 mm.  Here's a photo of the same snail, with more of the rock surface (and associated organisms) for scale:

I thought it would be fun to introduce you to this snail because it has "a trick up its sleeve."

Below is a close-up, showing the pale shell, the long foot (trailing behind the shell), and the anterior end with two tentacles, two dark eyes, and a gold-flecked siphon between the eyes.

Note also the edge of the mantle the darker band (brown and gold) along the margin of the shell.

When a Pear Marginella senses a predator, it extends its mantle to cover its shell.  The mantle offers protection — e.g., a slippery surface and release of toxic chemicals.

Below is a short video clip of a Pear Marginella encountering a predatory sea star.  First you will see the snail exploring on its own.  Then you'll notice a portion of a sea star arm (with tubefeet) in the left corner.  Watch the snail raise its mantle up over its shell.  The slippery surface acts as a shield, likely making it difficult for the sea star's tubefeet to hold onto the snail's shell.  (Later, the snail also starts "running away" from the sea star very quickly!)

There's a bonus: The mantle is beautiful!  Brown, with orange, gold, and blue flecks. 

Pear Marginellas aren't the only snails that cover their shells with their mantles for defense, but they're certainly one of the prettiest!

P.S.  The "Pear" in the common name comes from the shape of the shell.  But I also love the translation of its scientific name "Granulina" means "little pearl." 

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