Dodging underwater volcanoes, scientists in a tiny submarine are combing the Pacific for the largest single-celled animal in the world.

Lisa A. Levin, a North Carolina State University biological oceanographer, has hunted the Xenophyophorea almost constantly since her first sighting of the fragile, fist-sized creature in 1984.

"These giant protozoans aren't just interesting because of their size; they may be critical players in the biology and chemistry of underwater volcanoes," she said.

Funded by the U.S. Office of Naval Research, Levin has been to the ocean floor several times to study environmental conditions on the volcanoes.

Xenophyophorea are very thin and stringy, consisting mostly of long strands of protoplasm inside a protective outer coating. Dozens of tiny sea animals live in the passageways of the honeycombed shell, which can vary in size from a few millimeters across to larger than a football.

Levin, an expert in benthic ecology -- the study of organisms on the ocean floor -- is trying to determine how the protozoans influence other animals in the intricate ecosystem of the deepest sea.

She said she believes the organisms act both as a trap for certain materials and as womb for larvae of other sea animals, which are frequently hatched in the protozoan's elaborate coat.

"I'd like to master the basic biology of the animal -- how it eats, how long it lives and how it reproduces," she said.

A better answer to how the xenophyophores live may begin to give oceanographers a more detailed picture of the basic biological and chemical processes of the sea.