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Gooseneck Barnacle (Pollicipes polymerus)



Gooseneck Barnacle (Pollicipes polymerus)
Order: Thoracica, Family: Scalpellidae

The gooseneck barnacle is found from the southern region of Alaska to Baja, California. The shell, or capitulum, of the gooseneck barnacle grows to be about two inches long. It is made up of small plates, which enclose its soft body. Inside the shell, the barnacle primarily consists of long segmented legs, intestines and stomach. The gonads are held within the stalk. The stalk also contains the gland that is used to produce the adhesive that allows barnacles to attach to rocks so well.



I. GEOGRAPHIC RANGE
  • The gooseneck barnacle is found from the southern region of Alaska to Baja, California.
II. PHYSICAL CHARACTERISTICS
  • The gooseneck barnacle can be distinguished by its long neck, or stalk. This part of its body is usually one inch long. The stalk has a leathery appearance with a texture of small bumps.
  • The shell, or capitulum, of the gooseneck barnacle grows to be about two inches long. It is made up of small plates, which enclose its soft body. Inside the shell, the barnacle primarily consists of long segmented legs, intestines and stomach. The gonads are held within the stalk. The stalk also contains the gland that is used to produce the adhesive that allows barnacles to attach to rocks so well.
  • The gooseneck barnacle ranges in color from reddish-brown to brownish-black. It can reach up to eight inches in length.
III. FOOD HABITS
  • The gooseneck barnacle is a filter feeder. Since its head is attached to a usually rocky surface, the gooseneck barnacle feeds by extending its legs, or cirri, from its "shell." It separates the valves of its shell and extends the feathery cirri into the water when the tide is in, or when water runs down rocks.
  • The gooseneck barnacle often orients itself to face the current. This explains why, when seen, most are facing the same direction.
  • Food is caught in a lassoing action of the cirri. Six pairs of cirri contract and force the food down towards the mouth. Many small hairs that line the sides of the segmented cirri help catch the food. These hairs also aid in the movement of food towards the mouth. Since food may be hard to come by at low tide, the gooseneck barnacle can use some of its cirri to pass food to its mouth while using others to catch and hold onto new prey when food is abundant.
  • The gooseneck barnacle will eat a variety of food and is not selective. Most of its diet consists of small organisms such as plankton, cypris larvae, small clams, hydroids and amphipods.
IV. REPRODUCTION
  • The gooseneck barnacle is a hermaphrodite, meaning it is equipped with both male and female reproductive organs. These organs mature at relatively the same rate in the gooseneck barnacles. Although it is hermaphroditic, it usually will not self-fertilize unless there are no other barnacles within about eight inches. It is better for them to crossbreed because it ensures the diversity of their population.
  • Once a female lays eggs, a pheromone is released letting those surrounding males know that she is ready. One barnacle will reach its penis over to a nearby barnacle to release sperm into the shell. Amazingly, it can reach about seven times the animal's diameter.
  • Once the eggs in a neighboring barnacle are fertilized, they are brooded in the mantle cavity. The gooseneck barnacle has a reproductive period of about eight months, and produces about three to four broods (five to seven are possible for a large barnacle.) Thousands of free-swimming larvae are then released into the ocean to fend for themselves. These larvae are weak swimmers that spend their time feeding mostly on phytoplankton. Once they reach the cyprid stage they are strong-swimming, non-feeding larvae, with a sole purpose of finding a place to settle.
  • Gooseneck barnacles follow many cues for settlement. Once the cypris larvae have undergone metamorphosis to juvenile barnacles, they will search for a suitable home. They do so by receiving chemical cues from other established barnacles, which tell them that there are good conditions. However, this could be a problem when competing for space. They also have to take into consideration the correct temperature, surface texture and current. All of these factors are crucial for its survival.
  • Gooseneck barnacles are thought to reach maturity at the age of five, and are considered fully grown at the age of twenty.
V. BEHAVIOR
  • The flexible neck of the gooseneck barnacle will readily pull in when touched. This is a form of protection against predators. It can pull in its softer stalk so as to protect itself from getting eaten.
  • They also keep their shells closed unless they are eating. This helps prevent desiccation. They can then keep water enclosed inside until water is next accessible.
  • A small limpet a conical mollusk is often found on gooseneck barnacles' plates. It does not harm the barnacle.
VI. HABITAT
  • The gooseneck barnacle is found on rocky cliffs in the splash zone. They inhabit very high-energy environments because they can withstand the wave pressure very well. They receive minimal exposure to water at most, once a day. They are most often found within cracks and crevices in rocks to minimize their exposure to sunlight, which helps prevent desiccation.
  • The gooseneck barnacle is most commonly found in colonies of many other gooseneck barnacles. They often grow on each other. You can find many smaller goosenecks on the stalk of larger ones. Within the colony the larger goosenecks are found in the center surrounded by the smaller ones in the periphery. They are also very likely to be seen amongst California mussel beds.
VII. ECONOMIC IMPORTANCE FOR HUMANS
  • Positive
    The gooseneck barnacle is a barnacle that is found in the intertidal region of Portugal and Spain. There they are considered a delicacy and are served in gourmet restaurants. Due to local harvesting, their populations become depleted at times. They then seek sources outside of their countries and will then import a U.S. variety of barnacle as a substitute for the native gooseneck barnacle, thus bringing in money for the United States.
      VIII. CONSERVATION
      • The gooseneck barnacle is not endangered and is abundant along the Pacific coast. The only risk of lowering numbers is if the gooseneck barnacles are overused as a food source for humans.
      IX. OTHER COMMENTS
      • The gooseneck barnacle is a main food source the glaucous-winged gulls. The gulls eat them on exposed shores, eating the head and leaving the stalk. They are also a food source for sea stars and whelks.
      • Gooseneck barnacles are called such because of their long necks, which resemble those of geese. There are many myths that explain the naming of gooseneck barnacles. One myth says that geese grow from these barnacles, evident from the featherlike cirri that grow from their shells.



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