The Rough Keyhole Limpet lives low on rocky beaches around Puget Sound. Shaped like a tiny volcano, the Limpet shell is 2 to 3 inches long and ridged with a hole in the center. The keyhole, used to eject water and waste, separates this limpet from the so-called "true" limpets, which look similar but whose biology is quite different.

This hat-shaped critter is in the class of creatures called "Gastropods," which includes land snails and slugs. Limpets travel on a muscular foot and have a tongue-like "radula" studded with many tiny teeth. With this radula, they graze algae and colonial animals such as bryozoans and crust-like sponges. As the Limpet's front teeth wear out, back ones move up to replace them.

Almost all Keyhole Limpets have a tiny scale worm hidden between their foot and a fleshy body part called the "mantle." From this snug home, the worm feeds on left-overs and helps the limpet by nipping the feet of attacking sea stars.

Be careful as you walk along the intertidal zone on low tide days. To hold in the moisture they need to breathe, Limpets hunker down tight on rocks when the tide is out. Knocking them from their spot will cause them harm.