These sedentary creatures lock onto (or into) objects and animals and include more than 1,000 species, most of which are marine crustaceans.

Barnacle coming out of shell

Legs turn into food-grabbing organs

That’s right! Barnacles begin their lives as swimming larvae and eventually attach to a hard surface (such as rocks, wood, animal shells, coral, etc.—and sometimes, for parasitic species, softer homes like a shark’s belly!). Once anchored, they metamorphose some of their swimming legs into feathery retractile organs called cirri, which they use to capture little food particles floating by.


Female? Male? Both!

Most, but not all, barnacle species are hermaphrodites, meaning they contain both female and male reproductive organs. While they do occasionally self-fertilize, most barnacles fertilize with a nearby barnacle in a process called cross-fertilization.

Barnacles on the beach surrounded by kelp

Invading ships and shells

Barnacles both attach themselves to and burrow inside objects. You may have seen them on a variety of surfaces—covering pilings and rocks or clinging to the hull of a ship or the outside of a crab; they even attach themselves to larger animals like whales. But what you might not have seen are burrowing barnacles. Some species live as parasites by invading host bodies, such as crabs and cnidaria, or occupying the inside of a hermit crab’s shell.


A crustacean by many names

Gooseneck barnacles, acorn or rock barnacles, burrowing barnacles, wart barnacles—these are the common names for some barnacle species. They vary in shape: some are stalked, some are not, some have symmetrical shells, some look like fungi.


Other Invertebrates


You can see both warm- and cold-water corals at the Seattle Aquarium.

Tide pool ecosystems

Tide pools are found on rocky beaches in the strip of land between high and low tide, called the intertidal zone.

Moon Jelly

Jellies have been around for hundreds of millions of years!

Sea Anemone

These creatures can survive at depths of more than 32,000 feet.

Hermit Crabs

There are over 500 species of hermit crabs around the world.