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Comb Jellies: Ctenophora

Sea Walnut (mnemiopsis Leidyi): Species Accounts

Physical characteristics: Sea walnuts reach a length of about 4 inches (10 centimeters). Four deep furrows run from the top to bottom of the animal.

Geographic range: Sea walnuts live off the eastern shores of North and South America and have been introduced into the Black Sea.

Habitat: Sea walnuts live in shallow waters near shore and in bays and estuaries (EHS-chew-AIR-eez), the areas where rivers meet the sea.

Diet: Sea walnuts eat barnacle larvae, tiny crustaceans, fish eggs and larvae, and other animal plankton.

Behavior and reproduction: Sea walnuts spend most of their time actively swimming. Scientists do not know how sea walnuts reproduce.

Sea walnuts and people: Accidental introduction of sea walnuts into the Black Sea during the 1970s caused the collapse of fishing in Accidental introduction of sea walnuts into the Black Sea during the 1970s caused the collapse of fishing in that area. (Illustration by Joseph E. Trumpey. Reproduced by permission.) that area, and many people lost their jobs. The fish could not survive because the sea walnuts had eaten their food. To control the invader, scientists brought in another species of comb jelly—one that feeds on sea walnuts. By 2004 sea walnuts had invaded the Caspian Sea, and scientists were considering the same means of control.

Conservation status: Sea walnuts are not threatened or endangered. ∎



Carson, Rachel. The Edge of the Sea. 1955. Reprint, Boston: Mariner, 1998.

Niesen, Thomas M. The Marine Biology Coloring Book. 2nd ed. New York: HarperResource, 2000.

Silverstein, Alvin, Virginia Silverstein, and Robert Silverstein. Invertebrates. New York: Twenty-First Century, 1996.

Web sites:

"'Alien' Jellyfish Threatening Caspian Sea." U.N. Wire. http://www.unwire.org/UNWire/20040310/449_13861.asp (accessed on January 29, 2005).

Amos, William H. "Venus's Girdle." Microscopy-UK. http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmay04/wavenus.html (accessed on January 29, 2005).

Mills, C. E. "Ctenophores." University of Washington. http://faculty.washington.edu/cemills/Ctenophores.html (accessed on January 29, 2005).

Additional topics

Animal Life ResourceJellyfish, Sponges, and Other Simple AnimalsComb Jellies: Ctenophora - Physical Characteristics, Behavior And Reproduction, Venus's Girdle (cestum Veneris): Species Accounts - GEOGRAPHIC RANGE, HABITAT, DIET, COMB JELLIES AND PEOPLE, CONSERVATION STATUS