LAMPSHELLS: Brachipoda

PHYSICAL CHARACTERISTICS

Lampshells live as individual animals. Their bodies are completely enclosed, above and below, by a pair of shells. Each shell is called a valve. The phylum is divided into two distinct groups, or classes. In class Inarticulata, the valves are not hinged together. Instead, muscles keep them together. In the Articulata, a special tooth-and-socket hinge joins the valves. The valves of individual lampshells are usually different sizes. The largest valves measure 0.039 to 3.54 inches (1 to 90 millimeters) across, and the outer surface is smooth, pitted, or spiny.

Nearly all lampshells are sessile (SEH-sill). Sessile animals attach themselves to surfaces and cannot move. Lampshells attach themselves to solid surfaces by a soft, flexible stalk, called a pedicel (PEH-dih-sel). The pedicel is part of the body wall and is connected to the lower valve. A few species with pedicels either do not attach themselves to anything or anchor themselves in loose sand so they can still move around. Species without pedicels glue themselves directly to objects.

Lampshells have crownlike ridges with sticky tentacles that surround the mouth. The lophophore (LO-fo-for) is used to help them to breathe, feed, and protect themselves. It is also used to remove body waste from inside the valves. The lophophores are circular, u-, or spiral-shaped. The body wall has special tissues that form the mantle lobes. The mantle lobes make the valves. They have an internal body cavity. The digestive system is u-shaped and may or may not have an anus. The nervous system includes two groups of nerve cells, one in front of, the other behind the mouth. A ring of nerves surrounds the upper portion of the digestive system, with nerves leading into each of the tentacles of the lophophore. The open circulatory system carries clear blood. The blood in open circulatory systems does not always stay inside of tubes, or vessels. Kidneylike organs help to remove waste from body fluids. They are also used to release eggs or sperm into the water.

GEOGRAPHIC RANGE

Lampshells are found in all oceans.

HABITAT

Lampshells live on the bottom of oceans with cold, moderate, or warm waters. They either attach themselves to hard objects or bury themselves in mud or sand. They are found along seashores to depths of 17,410 feet (5,300 meters).

DIET

Lampshells eat bits of plants, animals, and other organisms floating in the water. The sticky tentacles collect food from water flowing past the body in between the valves.

BEHAVIOR AND REPRODUCTION

Some species live in burrows in soft, sandy or muddy sea bottoms. When threatened, they close their valves and quickly pull themselves into the burrow by using the muscles in their pedicels. Some species live out in the open. They attach themselves to rocks with their very muscular pedicels and can pull themselves down toward the bottom if they are disturbed. Lampshells without pedicels attach their lower valves directly to hard, flat surfaces and usually live in groups.

Most species of lampshells require both males and females for reproduction. Eggs and sperm are released from the kidneylike organs into the water where fertilization takes place. Only in a few species do the eggs develop inside the valves. The newly hatched larvae (LAR-vee) have rows of bristlelike cilia (SIH-lee-uh) on their bodies. They swim, have distinct body regions, and may or may not resemble adults. Once they settle on the bottom, the larvae begin to make their own valves. Most species live less than two years, but some are known to live for six to ten years.

LAMPSHELLS AND PEOPLE

Some inarticulate lampshells are eaten by people living on islands in the eastern Pacific, from Japan to New Caledonia. Articulate lampshells are used by scientists to understand the fossil record. Fossils are impressions of ancient organisms left in mud that have become stone after million of years. These fossils also help us to understand how life has changed, or evolved, over millions of years.

LAMPSHELLS MUST COMPETE FOR FOOD AND SPACE

As a group, lampshells are very ancient animals, at least 600 million years old. More than 12,000 different kinds of fossil species are known. They reached their peak just over 300 million years ago, when they were one of the most abundant life forms. Since then, their numbers have declined. Some scientists think this is partly because they cannot compete with clams and scallops living in the same habitats.

CONSERVATION STATUS

No species is considered threatened or endangered.

BLACK LAMPSHELL (Hemithyris psittacea): SPECIES ACCOUNT

Physical characteristics: The hinged valves of adult black lampshells are small to medium in size, with a maximum width of 1.38 inches (35 millimeters). The brownish purple valves are thick and bulging. The lower valve has a long, curved beaklike projection. The lophophore has two spirals and an external support. There are two pairs of kidneylike organs. The pedicel is short. The digestive system is curved and does not have an anus.

Geographic range: They are found all around the North Pole, mostly in the Pacific and Atlantic Oceans.

Habitat: Black lampshells live in warm and cold waters near seashores, between depths of about 33 to 4,265 feet (10 to 1,300 meters).

Diet: They eat bits of plants, animals, and nutrients floating in the water.

Behavior and reproduction: These animals attach themselves to hard surfaces with their pedicels. The rear of each mantle lobe has special tissues that produce eggs or sperm.

Black lampshells and people: This species does not impact people or their activities.

Conservation status: Black lampshells are not considered threatened or endangered. ∎

FOR MORE INFORMATION

Books:

Audubon Society Encyclopedia of Animal Life. New York: Clarkson N. Potter, 1982.

Brunton, C., L. Howard, M. Robin, M. Cocks, and S. L. Long, eds. Brachiopods Past and Present. London and New York: Taylor and Francis, 2001.

Brusca, R. C., and G. J. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, 2003.

Periodicals:

Gee, H. "Lophophorates prove likewise variable." Nature (1995): 493.

Morris, S. C. "Nailing the lophophorates." Nature (1995): 365-366.

Web sites:

BrachNet. Brachiopoda and Brachiopodologists.http://paleopolis.rediris.es/BrachNet/ (accessed on March 29, 2005).