In the image below, barnacles cloak a vertical wall rising above a sand filled tide pool. You’ll encounter scenes like this on exposed coastlines around the world, wherever there is a rocky intertidal. Here, the barnacles are goose barnacles, Pollicipes polymerus. Look for them where surf crashes against jutting rocks and headlands.
Take a closer look at the barnacles; you’ll find limpets perched atop. In northern Oregon’s goose barnacle beds there’s a good chance the first limpet you’ll come across is Lottia digitalis. Picking them out among the barnacles takes a keen eye.
I’ll never get over the match of color and pattern between P. polymerus and the L. digitalis living on and among them. Lottia digitalis is the ribbed limpet, named after ribbing on the shell and its margins. That’s a tricky name though; notice that the shells shown in the images above lack the nominal ribbbing. Have they been smoothed by exposure to surf and sand? It’s easy to tell which way ribbed limpets are heading. Take a look at the shell; the head is under the apex. If you like a challenge, click on the images in the limpet gallery above and determine the direction of travel (though it’s fair to ask, how far you gonna travel on a barnacle shell?).
Lottia digitalis roams the moist low light conditions, scraping at a biological film that coats high intertidal surfaces. Should the limpet lose its grip and tumble into the tide pool below, Pachygrapsus crassipes, the lined shore crab, is waiting. Shore crabs care nothing for the fine tuned camouflage of the perched limpet.