Barnacle (Cirripedia)
Dan Aspinwall

Gooseneck Barnacle
Gooseneck Barnacle

1.Classificatioin/ Diagnostic characteristics

barnacle.gif(21) (JF)

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustasea
Class: Maxillopoda
Infraclass: Cirripedia

Barnacles are an unuasual crustacean that do not share many of the classic characteristics of a crustacean. Barnacles when not closely examined appear to be more closely related to Mullosks than other Crustaceans like Lobsters. They have a hard outer shell and use their legs to grab food from the water.
There are two types of barnacles: Goose Barnacles and Acorn Barnacles. Goos Barnacles have a distinct stalk connecting the main body to the environment around it with white scales and brightly colored edges. Acorn Barnacles don't have stalks and directly attach themselves to the hard environment around them. They are usually pale yellow or white and exist mostly in estuarine conditions or on wood. (12) (Shwetha)

2. Relationship to humans

Barnacles share very little with the barnacle (human?) in that they only share the kingdom animalia.

When barnacles secure themselves to a surface, they secrete an incredibly strong brown glue. This glue is being studied for its applicable use in dentistry. It blends with the tooth's natural color. Unfortunately, it has minimal application potential because of its slow rate that it cements to teeth compared to existing adhesives and its lack of acid resistance. However, with further research it could still be utilized as a possible dental adhesive. (5) (JLev)
Barnacles often settle on ship hulls and harbor installations. This causes encrustation (hard coating added) to the ships and increases friction as ships move, slowing ships down and causing more fuel to be used up. Ships are treated with plastic coating or anti-fouling paints with copper or mercury to prevent encrustation (13) (KG).
Barnacles are also food for humans especially in Spain and Portugal.The taste of barnacles reminded people of the fleshy part of a goose's neck and in fact the word barnacle comes from the species of geese called Branta leucopis. Also barnacles are used in a Chilean dish called curant(20)(NC).

3. Habitat and Niche

Most barnacles live in shallow water (Epipilagic Zone) along with the vast mojority of marine life. They can live in fresh or salt water and as adults attach temselves to a base such as rocks, buoys, or large marine organisms. They tend to live in huge groups for protection and reproductive purposes.

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Barnacles exemplify the biological concept of resource partitioning which is where one of two competing species occupies a different niche. Different barnacle populations can occupy different niches even if they are in close proximity. For example, the rock barnacles beat out the stellate barnacles because they grow much faster, but they cannot survive higher than a certain height in the water. The stellate then occupies the niche of the more deep water niche because the rock barnacles cannot. These two different barnacle populations occupy separate niches, living right next to each other. (1) (PS).



4. Predator Avoidance

====The barnacle has an extremely hard outer shell like other crustaceans and the opening on the top of the barnacle closes when a threat is sensed. The barnacle also tends to live in huge groups for safety in numbers. A study was conducted through the Biology Department at Kenyon College that found that those barnacles who practiced group-living spent less time in hiding than those who practiced solitary-living. Also, it was found that barnacles who lived in groups returned to foraging much more quickly than those living alone. So, by living in groups, many barnacles will gain fitness benefits by living with other barnacles, but they will experience a great predation risk by returning to foraging ([1] ) (E.S.S.).



5. Nutrient Acquisition

Out of the hole at the top of the barnacle protrudes several feeding appendages that hang in the water picking up nutrients and food for the barnacle.

These feeding appendages are known as cirri, which are basket-like limbs. When it is feeding, the barnacle's two plates that cover its top entrance open up and the cirri wave into the oncoming current of water to direct food into its mouth. (3) (JLev)

Being filter feeders, barnacles filter plankton and organic debris from the water. Food is digested in a one-way digestive tract, consisting of the mouth, stomach, and intestine, and as a result, wastes are eliminated through the anus. (10) (MC)
While submerged in water, barnacles use their feathery barbed legs to capture plankton and absorb oxygen.(23) (TM)



6. Reproduction and life cycle

The Female barnacle produces the eggs and are attached to the side of the female while awaiting the males sperm to fertilize them.
Barnacles have two distinct larval stages, the nauplius and the cyprid, before developing into a mature adult. The naupulius stage occurs when a fertilized egg hatches into a nauplius a one-eyed larva consisting of a head and a telson, the last division of the body of a crustacean, and containing no thorax or abdomen. (HSC)

Barnacles are hermaphroditic, meaning a single individual has both male and female parts. An adult barnacle has a long, tubular penis which it extends out when it is ready to mate. The gametes are not released into the sea; rather, barnacles can directly fertilize one another. Once the mate receives the sperm, the eggs are brooded - or looked after during development - until they develop into naupli (an early planktonic stage of a crustacean). The naupli - which can be produced in quantities of over 10,000 - are released into the water as plankton. (4) (JLev)

A barnacle's life cycle consists of a mobile larvae stage and a immobile adult stage. After hatching from their eggs, the nauplius, the larva stage of the barnacle, swims freely through the water. As they grow larger, they molt (shed their outer shell) until they reach the cyprid stage, the final larval stage. In this stage, the cyprid larva scurries around in search for a suitable rocky environment that it will attach to around fellow adult barnacles. When it finds the perfect home, the cyprid molts for a final time into an adult.(8) (AY)

7. Growth and development

All Crustaceans begin in a larveal stage.

The name of the larvae stage is nauplius. During the nauplius stage, the newly hatched barnacles swim around like zooplankton. Before they continue into the next stage of their life, the cypris stage, they molt many times. (15) (WSS)
Additionally all barnacles undergo a cyprides stage where they attract to other barnacle and find a spot where they stick to for the rest of their life. (ES)
After barnacles hatch out of their eggs, they develop into free-swimming larvae that resemble tiny crabs. They will secrete a gluelike substance, attaching themselves to a suitable substance, when it is time to molt into an adult. They secrete layers of lime (calcium carbonate) which can be yellow, red, purple, or brown. Forming at their tips are cirri, feathery appendages that sweep plankton and other food into the mouth, as they are now stationary and cannot move to get food. [2] (SM)

8. Integument

The shell of the barnacle is an extremely hard chitinous Exoskeleton that the barnacle relies on for protection from the environment. They possess a soft sack for a carapace called the mantel, which surrounds the body and produces a substance that creates a shell. The shell is made up of protective plates that interlock and fuse together to form a round or flat cone that gives the barnacle its outer appearance. (6) (BB-V)
The shell of a barnacle is made of limestone. When the shell becomes too small for the barnacle, the animal secretes a chemical that breaks down the inside of the shell while building onto the outside, thus making the enclosure larger. (7) (SJ)



9. Movement

The barnacle stays planted on its base for the entirety of its adult life. Instead, it relies on the movement of water in order to bring nutrients. Additionally, barnacles attacked to ships will experience movement along with the ship, which creates water movement that the barnacle requires. The barnacle can move from one area to another by releasing its hold on the surface that it is attached to and allowing the current to take it to another area. This is how barnacle larva gets transferred to new areas. (11) (AA)



10. Sensing the enviornment.

The opening at the top of the barnacle can detect a potential threat in the water and instantly closes.
The six pairs of legs, called ciri, sift the water for food. The ciri are covered with sensory hairs that sense plankton for the barnacle to eat. When the leg brushes past plankton the barnacle scoops it in. (14) (BS)
In addition to the hairs on the limbs of the barnacle being extremely sensitive to touch, an adult barnacle has a single eye that is most likely only capable of sensing the difference between light and dark. (17) (JF)

11. Gas Exchange

Apendages within the mouth of the barnacle act as gills and collect dissolved oxygen from the water. The same apendages are responsible for the release of carbon dioxide.
Barnacles lack gills, yet gas exchange is accomplished through diffusion across the thin exoskeleton of the barnacle's carapace, located in the mantle cavity. (16) (JF)

12. Waste removal

The organism's waste flows out of the top cavity of the barnacle.

The solid waste is released from the mantle of the barnacle, which surrounds the body and gives off a substance that forms the thick, protective plates of the cone-shaped shell. Inside the mantle is a chamber where the mouth and reproductive organs are located, as well as where waste is removed.6(JLau)



13. Environmental Physiology

====Because many adult barnacles reside in intertidal zones, they must be able to withstand the variable conditions that come with the constantly changing tide. When the tide is lower than where the barnacle is settled, the barnacle is at risk of desiccation and death by dehydration. Therefore, to protect themselves, barnacles pull their plates together, leaving only a small hole for gas exchange. This reduces evaporation, and greatly reduces the risk of death, as only the hottest summers will kill them.[3] (FZ)

14. Internal circulation

The circulation of blood around the barncale is not a closed system. The blood fills the entire animal and is pumped by a heart around the body.
====The barnacle, which lacks a heart or circulatory system of complex organisms, circulates body fluids through passages in muscles and other organs. Such circulation is called “lacunar,” or open circulation. Hemolymph, or blood, is pumped by a heart and irrigated through cavities, or lacunas, and draining tissues. Through its somatic musculature, the body’s muscles, pumping can occur. Nonetheless, in mature and advanced forms of barnacles, a nearly closed system of vessels develops. Throughout the barnacle, gas exchange can take place across thin cuticular surfaces, as many small barnacle lack discrete respiratory organs. For respiratory structure and feeding, water is circulated through the mantle cavity by the pumping movements. For respiratory organs, the strap like organs, or filamentary appendages, extend from the body wall and, in sessile (immobile) barnacles, broad extension of the mantle wall, or branchiae, extend. (AWC)[4]



15. Chemical Control

Little research has been done on analyzing the endocrine system of barnacles. One experiment analyzed the effects of neuropeptides and peptide hormones on the development of barnacle larvae. It was discovered that hormones play a large role in their development, including delaying the full maturation (metamorphosis into adult) and affecting cypris (larvae) settlement. (22) (DM)

Review Questions

1. What protects the stationary barnacle from predators? (LC)
2. What tactic do barnacles temporarily exposed to the air utilize so they do not die from dehydration? (BH)
3. How is the circulatory system of the barnacle different from closed systems? (Shwetha)

1. Hillis, David M. Principles of Life. Sunderland, MA: Sinauer Associates, 2012. Print.
6. "Barnacles and Relatives: Thecostraca - Physical Characteristics." Net Industries and Its Licensors, 2012. Web.
11. "Barnacle" 22 April 2008. <> 11 December 2012.
13. "barnacle." The Columbia Encyclopedia, 6th ed.. 2012. 11 Dec. 2012<>.

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