Sony F717 digital , tripod
380EX flash off-camera
9.7mm at f8
1/500 second, ISO 100

Sounds in the night
psitol shrimp Alpheus heterochaelis

This odd-looking critter confused me for a bit, after I caught her in the nearby sound. While the size of my finger, and thus appearing to be a crayfish of some kind, my web research showed that there are no species of saltwater crayfish. I was assuming it to be some small species of lobster, but couldn't locate a match.

Then I stumbled upon the name of 'pistol shrimp' (Alpheus heterochaelis), and the illustration matched nicely, especially that big misshapen claw. The amusing part was, I was researching something else, the loud and distinct clicks that would emanate from the tank every once in a while, mostly at night. I had eliminated several different species, and after hearing the same sounds while chasing crabs on snorkel trips, I was trying to determine what species of crab in my tank might be the producer. I never suspected this sheila, and my limited knowledge didn't connect the body shape with 'shrimp'.

The loud "snap" that they can produce is done with the claw, and rather than it being by the pincers clacking together, it's actually a pop from water pressure, an example of extreme cavitation that can stun prey. It can also produce a burst of light, though not apparently at the naked-eye level. But I've felt it, an actual tap on my fingers as I disturbed the shrimp – the snap seems to be largely for territorial warnings, though the pistol-hammer action of the claw is used to break open shellfish for food. Another image of a pistol shrimp can be found here.

While I had this little bugger, she rearranged my tank on a regular basis. The sets of fins (pleopods) she had underneath her tail were amazingly powerful, and she used them to distribute the sand in my tank (and in the bowl she was photographed within below) with the force of a mini leaf-blower.

pistol shrimp Alpheus heterochaelis tail