(Left) Radula of the deep sea limpet, Neomphalus
fretterae, Family Lepetidae
(Right) Radula of the slit shell mollusc, Scissurella
crispata, Family Scissurellidae
Scanning electron micrographs; reprinted courtesy of Dr. Carole S. Hickman,
Museum of Paleontology, University of California, Berkeley CA.
The deep sea limpet's tongue, or radula (above, left) is used to
scrape algae off rocky surfaces, and it is strong enough to bore a deep-set scar into the
rock to which the limpet attaches (see the superfamily, Patellacea). The recurved tooth is
hardened with iron and silicon oxides at its tip, in effect a sharp rasping tool. By
comparison (above, right), the feathery structure of the slit shell mollusc's
radula lacks hardened teeth. It is more suited to sweeping and filtering fine organic
debris from the soft sands along the bottom, where this mollusc normally lives --a
mode of living like that of the other slit shell molluscs (see, for example, the Pleurotomariidae family).