Acorn barnacle
The acorn barnacle is a unique, immobile crustacean found on rocky shores in cold to sub-polar coastal waters of the Northern Hemisphere. Unlike other barnacles, it lacks a stalk and directly attaches itself to surfaces using its hard, armor-like plates, typically numbering between four and six. These plates start white when the barnacle is young and turn grayish-yellow over time, influenced by algae growth. Acorn barnacles are filter feeders, using feathery legs called cirri to capture microscopic food particles while submerged in water, beating their cirri at a rate of up to 40 times per minute. They are hermaphroditic, allowing them to reproduce asexually through internal fertilization, where they exchange sperm with neighboring barnacles. After fertilization, the eggs develop for four months before the young nauplius stage is released to float and eventually settle among mature barnacles. Predators, including whelks and starfish, pose threats, and acorn barnacles typically live for about eight years. This fascinating species showcases adaptations for survival in challenging marine environments.
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Acorn barnacle
Unlike many other barnacles, the acorn barnacle does not have a stalk which attaches this creatures to surfaces. Instead of attaching itself with a stalk, the acorn barnacle attaches itself directly to the rocky surfaces along the world's shores. Almost 2,800 acorn barnacles may be attached to a single square foot (930 square centimeters) of rock.
Kingdom: Animalia
Phylum: Crustacea
Class: Cirripedia
Order: Thoracica
Family: Balanidae
Genus: Balanus
Species: Balanoides
The acorn barnacle, an immobile crustacean, inhabits the rocky shores of coastal waters in cold temperature to sub-polar latitudes of the Northern Hemishpere. This three-inch (7 1/2-centimeter) long creature attaches itself directly to the rocky shores with its hard, armor-like, outer plates. Each acorn barnacle generally has between four and six of these plates. The plates are typically white when an acorn barnacle is young, and grow grayish yellow with age. This change in color is due to the presence of algae.
In the center of these plates on top, is a trapdoor. This door closes to protect the acorn barnacle's soft inner parts from the harsh conditions of this creature's environment. The acorn barnacle generally only closes its trapdoor when the tide is out and the rock on which the acorn barnacle lives is exposed to the air. When the acorn barnacle is covered with water, the barnacle's feathery legs, called cirri, extend beyond its shell. Acorn barnacles can survive for relatively long periods outside of the water.
Like other barnacles, the acorn barnacle uses its cirri to catch food. The acorn barnacle beats its feathery cirri through the water in an attempt to strain microscopic food particles from the water. A single acorn barnacle may beat its cirri at a rate of up to 40 times per minute. Once food is caught in the cirri, the food is passed down to the inside of the shell where it is eaten and digested. This process of catching food is called filter-feeding. Since the acorn barnacle can only feed in this way when it is covered by water, acorn barnacles which live lower on the shore typically feed more often than those living high above the mid-tide level.
Like other barnacles, the acorn barnacle is asexual. This means it reproduces independently. The species, like other crustraceans reporduces via internal fertilization. As a hermaphrodite, or animal having both male and female sexual organs, the acorn barnacle can both give sperm and have its egg fertilized by the sperm of another acorn barnacle. This process of passing sperm to a nearby settled acorn barnacle is common among large clusters of acorn barnacles. Each acorn barnacle passes sperm to a neighbor and receives sperm from a neighbor. After this passing of sperm, each acorn barnacle has a fertilized egg within its shell. This egg develops for four months before leaving the acorn barnacle. At the time it leaves, the young acorn barnacle is in its nauplius stage. From leaving its parent, the nauplius floats through the current as it grows and develops. Eventually it changes into its final development stage before adulthood and sinks to the bottom. It finds a place to settle where there are mature acorn barnacles and plants itself among the masses. Eventually this young acorn barnacle is securely attached and safe from predators by its strong plates.
Many different kinds of sliding mollusks try to feed on the acorn barnacle. A snail-like creature known as a whelk is particularly dangerous to this animal. Acron barnables also face predation from starfish, who can easily rip open the hard shell exterior.
The life span of the acorn barnacle is about eight years.
Bibliography
“Acorn Barnacle.” Oceana, oceana.org/marine-life/acorn-barnacle. Accessed 13 Mar. 2024.
“Acorn Barnacle.” Monterey Bay Aquarium, 2024, www.montereybayaquarium.org/animals/animals-a-to-z/acorn-barnacle. Accessed 13 Mar. 2024.
Puget Sound Museum of Natural History. “Acorn Barnacle.” University of Puget Sound, 16 Nov. 2020, www.pugetsound.edu/puget-sound-museum-natural-history/exhibits/marine-panel/acorn-barnacle. Accessed 13 Mar. 2024.