Tonight's post starts with a fun video. Check out these wonderful sequences of a Twistclaw Pistol Shrimp (Alpheus clamator) that Eric filmed recently. [If you receive this post via e-mail and can't see the video below, click on the title of the post above to go to the website.]
Watch for a variety of things in the video, e.g., the small chromatophores (like polka dots scattered across the body), the heart beating, the antennules flicking, the long hairs on the claws. And note the two different types of claws, especially the larger, intriguing left claw:
Although Twistclaw Pistol Shrimp have now been recorded in Oregon, their distribution is generally more southern. We've only found a few in the Bodega Bay area.
Pistol shrimp are also known as snapping shrimp. So if you've heard of snapping shrimp, or even heard snapping shrimp yourself, this shrimp is a member of that group.
The common names refer to a remarkable ability (not revealed during the video). The oversized claw is very unusual — instead of being used for crushing or tearing, it can produce a loud snapping sound and powerful shock waves that stun its prey!
Although I'm not great with physics, here's a basic explanation of how it works. At the tip of the claw there is a "plunger". The "plunger" can be "cocked" — i.e., locked in an open position — but when released, the "plunger" hits a "socket" on the opposite side with such a powerful force that it creates an extreme high-velocity water jet (at ~60 mph!). A bubble forms in the low pressure area in the wake of the water jet. The bubble grows quickly, but then the high pressure surrounding it causes it to collapse on itself (also known as cavitation). All of this happens so quickly that when the bubble collapses, it emits heat, light, and sound, and it creates a shock wave that emanates from the claw. In addition to stunning prey, it's possible that pistol shrimp use the snapping sound for communication and defense of their burrows.
From the side, you'll notice that the large claw has an unusual shape. Below are two pictures, one showing the entire animal, and the second a close-up of the claw:
(These are different individuals, but it's the same species.)
From the side views, it's hard to interpret what's going on, but it's a little easier with two views from above. The first shows the claw in the closed position:
And the second shows the same claw with the "plunger" in the "cocked" position:
A slightly different angle allows you to see both the "plunger" and the "socket".
It's an amazing design and an incredible behavior. If you're lucky enough to find a pistol shrimp, listen carefully and take a close look at the claw!
P.S. We thought this might be an appropriate topic for the holiday. Happy Fourth of July!
