Scary Mollusk Mouths Had Humble Beginnings

The inside of a mollusk's mouth is a fearsome sight to behold. Most mollusks, from giant squids to predatory slugs, have radulas, or tonguelike structures covered with interlocking teeth that move like a conveyor belt to slice and steer prey down the throat. But a new analysis of 500-million-year-old fossils suggests that the earliest radulas were used merely to slurp up mud-covered food from the seafloor.

University of Toronto graduate student Martin Smith had been examining hundreds of fossil specimens of the Cambrian animals Odontogriphus omalus, a naked slug, and Wiwaxia corrugata, a soft-bodied bottom-dweller covered with spines and scales. (The creatures would have lived at about the same time as an odd shrimplike creature that could grow up to 6 feet (1.8) in length and was equipped with spiny limbs on its mouth for snagging prey.)

Scientists had been unsure about where these animals fit in the evolutionary tree, whether they were members of the groups Mollusca, Annelida, or a group containing molluks and annelids. The basis for the confusion had to do with the organisms' bizzare mouthparts, which resembled both the radula of mollusks and the jaws of some annelid worms.

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