MONOPLACOPHORANS: Monoplacophora

PHYSICAL CHARACTERISTICS

Monoplacophorans (mon-oh-plak-oh-FOR-ans) look like limpets, but their single round shell, or valve, is bilaterally symmetrical. This means that the valve has a distinct left side and a distinct right side. The point of the valve is located in the middle, just over the front edge. Depending on the species, the caplike valve varies from flat and shieldlike to a short, squat cone. The valve is mostly thin but becomes slightly thicker toward the edges. They measure 0.25 to 1.25 inches (3 to 30 millimeters) in length.

The head is small but distinct. There are no eyes, and the only tentacles are found next to the mouth. Behind the mouth is a round, muscular foot. The foot is located on the end of a short column and is not very strong. It is surrounded by a small groove called the mantle cavity. The mantle cavity has five or six pairs of gills used for breathing and separates the foot from the fleshy mantle. The mantle produces the mineral calcium carbonate that makes up the valve. There are three to seven pairs of kidneylike organs. Males and females have a pair of reproductive organs. The anus is located opposite the head at the end of the digestive system. The anus is the opening where solid waste leaves the body.

GEOGRAPHIC RANGE

They are found in the South Atlantic Ocean, Gulf of Aden, and several places in the eastern Pacific Ocean.

HABITAT

Monoplacophorans live on deep-sea bottoms at depths between 624 to 22,980 feet (190 to 7,000 meters). They are found attached to rocks and solid objects.

DIET

Monoplacophorans feed on bits of plants, animals, and other organisms.

BEHAVIOR AND REPRODUCTION

Nothing is known about their behavior.

Both males and females are required for reproduction. There are not any differences on the outside of their bodies to distinguish males and females. The eggs are thought to be fertilized in water, outside of the female's body.

MONOPLACOPHORANS AND PEOPLE

Scientist studying the origins of mollusks or how animals adapt to deep-sea life use monoplacophorans as research subjects.

MONOPLACOPHORANS IN THE FLESH

Monoplacophorans were once only known from fossils. These stone impressions preserved only the details of the hard valves of these ancient species, not their soft bodies. In 1952, a Danish expedition named "Galathea" dredged up ten living specimens from the deep waters off the Pacific coast of Mexico. Their never-seen-before fleshy bodies revealed the similarities of monoplacophorans to chitons and snails. The new species was given the name Neopilina galathea. Neopilina comes from the Greek neos, or new, and pilion, or little cap.

CONSERVATION STATUS

No monoplacophorans are considered threatened or endangered.

NO COMMON NAME (Laevipilina antarctica): SPECIES ACCOUNT

Physical characteristics: The transparent valve is small, thin, and somewhat flat. The point on the valve is shaped like a nipple. The surface of the valve near the point is fairly smooth but becomes more ridged toward the margins. The tentacles are short, swollen at their tips, and have approximately seven short and thick appendages. The mantle cavity has five pairs of gills. The foot measures 0.06 by 0.04 inches (1.5 by 0.9 millimeters) across when it is not expanded.

Geographic range: They are found in the Weddell and Lazarev Seas, off the coast of Antarctica.

Habitat: They live attached to rocks and old shells on sea bottoms at depths of 690 to 2,100 feet (210 to 644 meters).

Diet: They scrape up bits of minerals, plants, animals, and other organisms that settle on the sea bottom.

Behavior and reproduction: Nothing is known about their behavior or reproduction.

Laevipilina antarctica and people: They are studied by scientists.

Conservation status: Laevipilina antarctica is not considered threatened or endangered. ∎

FOR MORE INFORMATION

Books:

Brusca, Richard C., and Gary J. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, 2003.

Periodicals:

Warén, A., and S. Hain. "Laevipilina antarctica and Micropilina arntzi: Two New Monoplacophorans from the Antarctic." The Veliger 35 (1992): 165-176.

Web sites:

"Class Monoplacophora." http://animaldiversity.ummz.umich.edu/site/accounts/information/Monoplacophora.html (accessed on March 30, 2005).

"Class Monoplacophora." FactMonsterhttp://www.factmonster.com/ce6/sci/A0859721.html (accessed on March 30, 2005).

"Monoplacophora." http://www.biologydaily.com/biology/Monoplacophora (accessed on March 30, 2005).

"Shelled Marine Mollusks of Temperate Australia. Interactive Information and Identification." http://www.danceweb.com.au/marine/data/majgrps.htm#mono (accessed on March 30, 2005).

"Neopilina. A living fossil." http://www.weichtiere.at/Mollusks/Andere/neopilina.html (accessed on March 30, 2005).