Jaw Animals: Micrognathozoa

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JAW ANIMALS: Micrognathozoa


Limnognathia maerski is the only species of jaw animals. These animals are 0.004 to 0.006 inch (100 to 150 micrometers) long. The body is divided into a head, an accordion-like chest, and an abdomen. Jaw animals have plates between the cells of the body covering of their back and sides. The bottom surface of the animals is covered with hairlike fibers. The sensing system is a series of bristles. The digestive system is made up of a highly complex jaw, a simple intestine, and an anus (AY-nuhs) that rarely opens.


Jaw animals live in Greenland and between Africa and Australia 1,500 miles (2,400 kilometers) north of Antarctica.


Jaw animals live in moss or sand at the bottom of cold running or still freshwater.


Jaw animals eat bacteria, algae, and diatoms. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves. Diatoms (DYE-uh-tahms) are a type of algae that have a shell.


During their search for food, jaw animals move their head slowly from side to side, while the fibers on the head beat food particles toward the animal's mouth. Food that reaches the mouth is quickly grabbed by the bottom jaws, dragged into the mouth, and processed by the main jaws.

When they move, jaw animals either crawl or swim. While swimming, they move slowly in a spiral. When crawling, they glide slowly on the bottom. If disturbed, a crawling jaw animal stops and attaches to the bottom by using a sticky pad on its belly.

Jaw animals produce two kinds of eggs: a thin-shelled type and a thick-shelled type. Scientists believe the thin-shelled eggs are made by asexual reproduction and that the thick-shelled eggs are made by sexual reproduction, even though males have never been seen. One possibility is that jaw animals produce dwarf males that live only for a very short period and therefore have not yet been found. Another possibility is that jaw animals hatch as males and then quickly develop into females. Asexual (ay-SEK-shuh-wuhl) means without and sexual means with the uniting of egg and sperm for the transfer of DNA from two parents.


Jaw animals have no known importance to people.


Jaw animals are not considered threatened or endangered.


In Greenland jaw animals have been found only in cold springs that often are frozen for seven to eight months of the year. The island where they live has more than one thousand springs that maintain a constant temperature throughout the year and therefore run during the winter, but the jaw animals avoid this kind of spring. This finding suggests that the deep-freeze period is important for this animal's life cycle.


Jaw animals appear to be very choosy about what they eat. If by accident a jaw animal grabs and swallows an unwanted food, it quickly rejects it. Using a characteristic "vomit behavior," the animal lifts its forehead to a vertical position, pushes its entire jaw out of its mouth, and ejects the unwanted food.



Ruppert, Edward E., Richard S. Fox, and Robert D. Barnes. Invertebrate Zoology. 7th ed. Belmont, CA: Thomson-Brooks/Cole, 2004.

Web sites:

"Jaws: New Animal Discovered." Science Now.http://www.calacademy.org/science_now/archive/headline_science/new_critter_120700.htm (accessed on February 20, 2005).

"Micrognathozoa: A New Microscopic Animal Group from Greenland." Zoological Museum in Copenhagen. http://www.zmuc.dk/InverWeb/Dyr/Limnognathia/Limno_intro_UK.htm (accessed on February 20, 2005).