Kingdom – Animalia
Phylum – Arthropoda
Subphylum – Crustacea
Class – Maxillopoda
Subclass – Thecostraca
Infraclass – Cirripedia
Superorder – Thoracica
Suborder – Balanomorpha
Superfamily – Balanoidea
Family – Archaeobalanidae


Balanus balanoides, otherwise known as the northern rock barnacle or the acorn barnacle, is the only sessile crustacean. Barnacles will attach to almost any surface that is consistently submerged by brackish or saltwater. In their larval nauplius stage, barnacles swim around as zooplankton and feel around for a suitable spot with their adhesive antennae. The barnacle then secretes calcium carbonate, which grows to form the hard shells that constitute the familiar form of the barnacle. Four of the plates combine to form a door, which can be opened or closed by the muscles of the barnacle so that it can extend its long, feathery cirri to catch planktonic food particles. The gills of the barnacle are located on these cirri as well. Barnacles are hermaphrodites, but they still need to reproduce sexually with a neighbor. They accomplish this using a retractable tube of semen that can extend up to six inches to another barnacle. The barnacle has only one eye, which is primarily sensitive to light and dark. The hairs on the cirri are another source of sensory information.



A – cirri

B – penis

C – anus

D – testicle

E – mantle

F – antennae

G – channels from cement glands

H – cement gland

I – ovary

J – mantle cavity

K – oviduct

L – eye

M – mouth


A – non-movable plate

B – movable plate

C – attached base


“Barnacles.” Woods Hole Oceanographic Institution. Web. 16 Nov. 2015. <>.

White, N. (n.d.). An acorn barnacle – semibalanus balanoides – general information. Retrieved November 17, 2015, from