Pollicipes polymerus, the leaf barnacle, clustered in a group of mussels on Vancouver Island, BC. (There are more than 25 barnacles in this image. Individuals can be identified by the red-colored opening of the shell plates.) Each individual has a long, fleshy stalk to both attach the barnacle’s body to the rock and allow it access to water rich in oxygen and plankton washing around the cluster. In several cultures that fleshy stalk is cooked and enjoyed. The most famous biologist to study barnacles (thus far) is Charles Darwin.
The round lump is the owl limpet, Lottia gigantea, on a rock in Santa Cruz, CA. Barnacles, limpets, and algae have all settled onto the limpet’s shell, taking advantage of the secure substrate the shell provides. The lines marking the rock are the result of the limpet snacking: the dark marks are an algal film that has covered the rock; the lighter lines are scratches into that algae made by the limpet’s scraping teeth (radula). This species keeps a local algae “farm,” but may retreat into hiding at low tide. Finding these scratch marks is evidence an owl limpet is nearby. (For scale, the limpet in this photo is about 5 cm long.)
An overhead view of a cluster of tube worms, Eudistylia sp., at low tide show tubes that falsely appear empty. Each tube is about 20 cm (8 in.) long and has a flexible texture likened to leather. The worms do not emerge from their tubes during low tide aerial exposure. Their feather-like feeding structures resembling pom-poms will stick out of tube ends once the worms have been submerged by the incoming tide.