Group of Gooseneck barnacles
Close up of Gooseneck barnacles Group of Gooseneck barnacles, smaller Acorn barnacles to left and Buckshot barnacles in lower sections Gooseneck barnacles clumping on side of rock Gooseneck barnacles in field of mussels with other smaller barnacles and limpets Gooseneck barnacles on exposed side of rocks Clump of Gooseneck barnacles on exposed rock Gooseneck barnacles along with Red Thatched barnacles Close up of feeding structure ( Cirri ) in Gooseneck barnacle

Gooseneck Barnacle (Pollicipes polymerus )

Gooseneck Barnacles are a common sight in the exposed areas of the middle intertidal zone. They can be identified by several light colored plates that form the top of a cone that sit on top of a dark stalk. These barnacles are typically found in large clumps and often in the midst of mussels. Gooseneck barnacles can grow several inches long depending on the conditions.
Red Thatched Barnacle
Group of Red Thatched Barnacles on rocks Red Thatched Barnacles in group of mussels and smaller buckshot barnacles Single Red Thatched Barnacle. Notice closed mouth parts on top. Two Red Thatched Barnacle next to Acorn Barnacles Red Thatched Barnacles next to Acorn Barnacles and smaller buckshot barnacles attached to Red Thatched. Single Red Thatched barnacle in field of buckshot barnacles and limpets

Red Thatched Barnacle (Tetraclita rubescens )

These barnacles appear reddish in color and have a rough or corrugated outer shell. Adults of this species are typically between ½ and 1 inch in diameter. They live in similar places as other barnacles on exposed rock surfaces. A similar species is the Red Stripped barnacle that is more stripped that a solid reddish color. ( other names: Volcano barnacle )
Close up of Acorn barnacle
Acorn and smaller buckshot barnacles Single large acorn barnacle with smaller buckshot barnacles and periwinkle snails Acorn and smaller buckshot barnacles Acorn and smaller buckshot barnacles

Acorn Barnacle ( Balanus spp )

These barnacles are small animals that typically live in the mid to upper tidal zone. The color ranges from white to light brown in color. The average adult size is about 1/4 to 1/2 inch wide. They look like a tiny mountain that is a bit larger at the base and tapers near the top. There is an opening at the top where the feeding tentacles emerge. A similar species is the Buckshot Acorn barnacle but the adult size is much smaller.
Close up of buckshot barnacle
Buckshot barnacle on mussel along with larer Red Thatched barnacle BBarnacles will live almost anywhere, even on an Owl Limpet Buckshot barnacles Close up of buckshot barnacles and a few periwinle. Most are 1/4 inch Buckshot barnacles on side of rock

Buckshot Barnacle (Chthalamus spp )

This barnacle closely resembles the Acorn barnacle except that it is much smaller. They can live one most any surface where they can attach to. These barnacles range from 1/8 to 1/4 inch wide for adults. This includes many other animals like limpets, snails, mussels and even other barnacles. Chthalamus has an oval shaped opening whereas the Balanus is diamond shaped. They can settle in very high densities that will cover entire areas of rock. ( other names: grapeshot barnacle, Acorn )
Megabalauns barnacle
Megabalauns barnacle Megabalauns barnacle

Megabalanus (Megabalanus californicus )

This is the most colorful barnacle in the intertidal zone. This particular barnacle lives primarily in the subtidal region and seldom seen in a natural state. The shells of this barnacle however are commonly found attached to mussels that have washed ashore. The shell is red and white stripped and typically found in small groups


Description – Barnacles come in two basic shapes. The Gooseneck barnacles have a set of whitish plates that form a cone on top of a long stalk. The other basic form is that of a small short and stocky cone shaped shell that becomes smaller near the top. There is an opening at the top where feeding and respiratory appendages are exposed. Acorn barnacles and Red Thatched barnacles have this body shape.

Barnacles are crustaceans and are related to crabs and lobsters. They have a hard exoskeleton and multiple segmented legs. These segmented legs however have become specialized feeding and respiratory appendages and no longer function as legs. Barnacles also grow a hard outer shell in addition to the exoskeleton. It’s this hard outer shell that is what is visible. These sessile crustaceans also have an opening at the top of the animal where the specialized feeding appendages are exposed to water.

Feeding – Barnacles all have specialized legs ( Cirri ) that are used for feeding. The barnacles will open the top of the shell and extend the Cirri into the water. Small bits of food are then trapped in the Cirri and moved to the mouth area. The barnacles will only extend these feeding appendages when covered with water.

Protection – the most obvious protection for barnacles is the hard outer shell. This protects the animal from predators but also allows barnacles to survive exposed to air. The shell keeps water trapped within the shell and the animal can use the oxygen in the trapped water for respiration. Barnacles also have several plates at the top of the shell that they use to open and close the opening. These plates when closed form a tight seal that protects that animal from drying out and predation. The primary predator of barnacles is sea stars. Predatory snails will also feed on barnacles.

Ecology - Barnacles have a multistage life cycle. The recently fertilized eggs will live in the water column for several weeks. The larval barnacles drift to some extent in the open ocean and when conditions are right, they will settle on a hard surface and undergo a transformation. The larval barnacle will settle on its head and cement itself to the substrate. The legs and the rest of the body undergo a radical transformation similar to that of butterflies.

The result of this transformation is the adult barnacle. The feeding legs ( Cirri ) are actually the bottom end of the animal and the head is attached to the rock or other hard surface. Barnacles will only settle and begin the transformation when conditions are right. This includes temperature and proximity to other barnacles in some instances.

Like other crustaceans, Barnacles will molt periodically to grow. The molting process begins with the animal making a small crack in the hard exoskeleton ( not the shell that is visible ). Once the crack is large enough, the animal climbs out and the body expands for several days. A new exoskeleton then hardens and the process will repeat periodically.
Posted in Animals.