Life at the Edge of the Sea

Acorn barnacles are characteristic of the spray zone on most rocky coastlines, although some species, such as Austromegabalanus nigrescens, occur at the lower edge of the intertidal zone. Sometimes mistaken for molluscs, they are in fact crustaceans. This is Catomerus polymerus, another acorn barnacle from south eastern Australia.

Stalked, or goose barnacles, which grow on ship hulls, look quite different from these acorn barnacles: they are colonial and are joined together by structures that look like grey intestines. Photograph by J. Smissen.