Snorkel in the sand

 Okay, here's the mystery photo from last night:

 

 

This is a tricky one, and I'll admit I wouldn't have known what it was myself (until now!).

 

The next photo will show more of the animal.  I'm guessing you'll be familiar with it, although you might not have observed this species in action under water:

 

 

 

This is a Purple Olive Snail (Callianax biplicata, formerly Olivella biplicata).  Purple Olive Snails live on sandy beaches and the snails are often buried below the sand, so they might not be visible (except for their winding trails).  Their shells are sometimes washed ashore.

 

While burrowing, this snail had its siphon extended above the surface of the sand like a snorkel.  The siphon provides access to water which will be drawn into the mantle cavity of the snail, passing over the gill.  The water will also flow by sensory receptors that can detect waterborne cues — picking up information about things like food, other snails, possible predators, etc.

 

Here's one more photo showing a bit more of the shell:

 

 

The next time you see an olive snail, if it's under water, you can look closely for the small tubular siphon in front of the snail!

P.S.  Thanks to Eric for the great photos!