- Also called:
- brachiopod
- Key People:
- Thomas Davidson
- Related Topics:
- Inarticulata
- Stricklandia
- Tuvaella
- Eocelia
- Articulata
lamp shells
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What are lamp shells?
Lamp shells, also known as brachiopods, are marine invertebrates that dwell on the sea floor. The name "lamp shell" comes from their resemblance to ancient Roman oil lamps. They possess two bilaterally symmetrical valves, or shells, of unequal size that cover their dorsal and ventral sides.
Though lamp shells were once abundant, they are not as numerous today. Lamp shells first appeared in the Cambrian Period, approximately 542 million years ago. Aside from dating geological periods, they have no economic value except as curios and museum pieces.
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Where do lamp shells live?
Lamp shells, also known as brachiopods, are bottom-dwelling marine invertebrates found in all oceans. These creatures have two bilaterally symmetrical valves, or shells, of unequal size that cover their dorsal and ventral sides.
Though not as abundant as in the past, lamp shells have existed from the Cambrian Period to the present. One extinct genus, Leptodus, lived in shallow Permian seas of North America and attached itself to the sea floor or other shells. Today, lamp shells are primarily of interest as curios, museum pieces, and for dating geological periods.
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How do lamp shells protect themselves?
Lamp shells, also known as brachiopods, are marine invertebrates that protect themselves with two hinged valves, or shells. These shells, which resemble early Roman oil lamps, provide a protective covering for the animal.
Like other mollusks, sea squirts, and barnacles, lamp shells can retract their soft body into their protective shell. The valves of inarticulate brachiopods are held together by muscles. When startled, lamp shells can contract their pedicle, a fleshy stalk, to retract into their burrow for protection.
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What do lamp shells eat and how do they get their food?
Lamp shells, also known as brachiopods, are marine invertebrates that eat minute organisms or organic particles. They get their food using a lophophore, a horseshoe-shaped organ with hair-like structures called cilia that filter food particles from the seawater. The brachiopod opens its shell, and the cilia lash to bring in food-bearing currents. Food particles, often trapped in mucus, move along lophophore grooves to the mouth. Some brachiopod shells have a trilobed anterior that separates incoming food-bearing currents from outgoing, waste-bearing currents.
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How are lamp shells different from clams and other shellfish?
Lamp shells, or brachiopods, are marine invertebrates with two shells, similar to clams and other shellfish. However, unlike clams with valves on their left and right sides, lamp shells have valves on the dorsal (top) and ventral (bottom) sides. Also, the valves of lamp shells are bilaterally symmetrical, meaning each valve has mirror-image sides, whereas clam valves are asymmetrical.
Lamp shells have a lophophore, a horseshoe-shaped feeding structure with ciliated filaments that direct food to the mouth. Clams, as bivalves, possess gills adapted as filtering devices to extract food. Lamp shells attach to surfaces via a pedicle, a fleshy stalk, whereas clams use a byssus, a larval structure, for attachment.
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Why are lamp shells important for scientists studying Earth's history?
Lamp shells, also known as brachiopods, are marine invertebrates with two bilaterally symmetrical valves. They are called lamp shells because they resemble early Roman oil lamps. Lamp shells are important to scientists studying Earth's history because their fossil representatives allow them to survey their evolution from the Cambrian Period (about 542 million years ago) to the present. They are useful in dating geological periods.
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lamp shells, any member of the phylum Brachiopoda, a group of bottom-dwelling marine invertebrates. They are covered by two valves, or shells; one valve covers the dorsal, or top, side; the other covers the ventral, or bottom, side. The valves, of unequal size, are bilaterally symmetrical; i.e., the right and left sides are mirror images of one another. Brachiopods (from the Greek words meaning “arm” and “foot”) are commonly known as lamp shells because they resemble early Roman oil lamps.
Brachiopods occur in all oceans. Although no longer numerous, they were once one of the most abundant forms of life.
Members of this phylum first appeared rather early in zoological history. It is possible, by means of fossil representatives, to survey their evolution from the Cambrian Period (about 542 million years ago) to the present. Although some of the evolutionary development is revealed, it is still imperfectly understood. Other than their usefulness in dating geological periods, members of this phylum have no economic value, except as curios and museum pieces.
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General features
Size range and diversity of structure
Most brachiopods are small, 2.5 cm (about 1 inch) or less in length or width; some are minute, measuring 1 mm (more than 1/30 of an inch) or slightly more; some fossil forms are relative giants—about 38 cm (15 inches) wide. The largest modern brachiopod is about 10 cm (4 inches) in length.
Great diversity existed among brachiopods in the past; modern brachiopods, however, exhibit little variety. They are commonly tongue-shaped and oval lengthwise and in cross section. The surface may be smooth, spiny, covered with platelike structures, or ridged. Most modern brachiopods are yellowish or white, but some have red stripes or spots; others are pink, brown, or dark gray. The tongue-shaped shells (Lingula) are brown with dark-green splotches; rarely, they are cream yellow and green.
Distribution and abundance
Today, brachiopods, numbering about 300 species representing 80 genera, are abundant only locally. In parts of the Antarctic they outnumber all other large invertebrates. They are common in the waters around Japan, southern Australia, and New Zealand. Although rare in the Indian Ocean, some unusual types are common along the coast of South Africa. In Caribbean and West Indian waters, 12 species occur. The east and west coasts of the North Atlantic Ocean are sparsely occupied by brachiopods; the waters around the British Isles contain a few species, and a few genera live in the Mediterranean Sea. The West Coast of the United States and Hawaii have a number of brachiopod species, and the coasts of Chile and Argentina have a considerable variety, including the largest living species. Some live in the polar regions, and a few are abyssal; i.e., they inhabit deep parts of the ocean.
Natural history
Reproduction
Not much is known about the reproduction of brachiopods. Except in three genera, the sexes are separate. Eggs and sperm are discharged into the mantle cavity through funnel-shaped nephridia, or excretory organs, on each side of the mouth. Fertilization takes place outside the shell. In a few genera the young develop inside the female in brood pouches formed by a fold of the mantle, a soft extension of the body wall. Some fossil forms had internal cavities that may have served as brood chambers. The egg develops into a free-swimming larva that settles to the bottom. The free-swimming stage of the articulate brachiopods (whose valves articulate by means of teeth and sockets) lasts only a few days, but that of the inarticulates may last a month or six weeks. In inarticulate larvae the pedicle, a stalklike organ, develops from a so-called mantle fold along the valve margin; in articulates it develops from the caudal, or hind, region.
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Behaviour and ecology
About 60 percent of brachiopods live in shallow water (less than 100 fathoms—about 180 metres [600 feet]) on the shelf areas around the continents. More than 35 percent occupy waters deeper than 100 fathoms, and a few live in the abyss down to more than 6,000 metres (about 20,000 feet). Lingula lives from the tidal zone to 23 fathoms (about 42 metres [138 feet]). Most modern branchiopods anchor by the pedicle to pebbles, to the undersides of stones, or to other hard objects. They prefer quiet water and protected surroundings. Lingula lives in mud or sand and is attached at the bottom of its burrow.
Brachiopods feed by opening the shell and bringing in food-bearing currents by lashing of the cilia (hairlike structures) attached to the filaments of the lophophore, a horseshoe-shaped organ that filters food particles from the seawater. Cilia in lophophore grooves bring food particles, often trapped in mucus, to the mouth. Brachiopods feed on minute organisms or organic particles. Articulate brachiopods, which have a blind intestine, may depend partly on dissolved nutrients.
Shells of some articulate brachiopods have a fold, which forms a trilobed anterior that helps keep lateral, incoming food-bearing currents separated from outgoing, waste-bearing currents. When feeding, Lingula protrudes its anterior (front) end above the mud and arranges its setae (bristle-like structures) into three tubes. These channel the water into lateral incoming and medial, or central, outgoing currents. Some coralliform brachiopods of the Permian Period (299 million to 251 million years ago) are thought to have fed by rapid beating of the dorsal valve, causing a sucking in and expulsion of food-bearing water. Some ostreiform (oyster-shaped) types of the same period are believed to have fed by gentle pulsation of the dorsal valve.