Here's one microbe that has scientists turning their heads

They thought of naming it Rubber Neckia, but decided that really wasn't good enough. ''In fact,'' observes microbiologist Sidney Tamm of the Marine Biological Laboratory here, ''it wouldn't begin to do it justice.''

What has left biologists scratching their collective heads looking for a suitable name is a microorganism a few thousandths of an inch long that is trumping a multitude of cherished biological theories. Among other characteristics, the protozoan sports a protruding ''head'' that spins clockwise at a constant 30 revolutions per minute.

How a lump of protoplasm manages to perpetually swivel without twisting its head off - as a true ''rubber neck'' would be expected to do - is a mystery. But as it is the first solid proof of a cell's fluid nature, amazed biologists have been rewriting textbooks to include the little wonder.

For the last decade, since he accidently discovered the organisms in termites that were infesting a friend's grapefruit tree, Dr. Tamm has spent more than half his research time scrutinizing the single-cell organism.

''It's become a sort of ongoing crusade,'' he says, to understand the protozoa and to convince skeptical biologists it wasn't some kind of trick.

''I remember leading one colleague to the microscope,'' recalls Tamm with an exasperated shrug. ''He looked through the eyepieces for a few minutes, turned to me, and said quite seriously, 'I won't believe it - I refuse to believe it,' and that was that.''

With the perseverance of a scientist who knows he is right, however, Tamm managed to convince nearly all the skeptics. And recently, when his discovery was picked up by such science publications as Britain's Nature and Scientific American, he knew it had won hard-fought acceptance.

This has encouraged him to forge ahead and try to unlock the secrets of this protozoan, known now by its general family name of devescovnid flagella. In addition to its novel swiveling feature, the devescovnid is providing one of the most outstanding examples of symbiosis - the mutual interdependence of two or more organisms - in the natural world.

Wood-eating termites depend on protozoa such as this one to help them digest cellulose from trees. Without such organisms, the termite would starve. That has been known since the 1920s. What is new is that this particular devescovnid depends not on the four, whiplike flagella splayed from its rotating nose-cone for mobility, but on the hairlike flagella of countless tiny bacteria arrayed on its surface.

''One scientist likened (the tiny bacteria) to microbial galley slaves,'' Tamm recalls.

This specific devescovnid is the only example in nature where a cell with a nucleus is pushed about by cells without nuclei.