Rostrate Barnacle

How to Distinguish from Similar Species: Balanus balanus has septae in the tubes of the wall plates. Balanus nubilus grows much larger, usually has heavily eroded plates, has longer beaks, and appears bright orange-yellow when it opens. Semibalanus cariosus has thatchlike projections on the outside of the plates. Balanus crenatus looks superficially similar but has no beaks.

Biology/Natural History: Fatty acid composition indicates that small individuals eat mainly detritus while larger individuals feed mainly on diatoms.

This subtidal barnacle has 6 plates and the rostrum overlaps the adjacent plates. Its terga are drawn out into a beak. The outside of the plates are fairly smooth or with shallow longitudinal striations, not much eroded. The base is well calcified. The tubes within the wall plates do not have transverse septa. The overlapping portions of the plates are usually glossy. Usually less than 3 cm diameter but may be up to 5 cm. In my experience this barnacle is usually as tall or taller than wide.

Depth Range: --below normal SCUBA depths.