Cast-Iron Foot: Undersea snail has mineral armor
Sid Perkins
An
as-yet-unnamed species of snail living around hydrothermal vents deep
beneath the Indian Ocean bears an unusual suit of armor forged from the
dissolved minerals spewing into its seafloor habitat.  | SULFIDE
SHINGLES. The iron—sulfide-encrusted scales on the foot of this snail
may protect it from predators in its hydrothermal-vent environment
(background of composite photo).
S. Bengtson and M. Segonznc |
The sides of the snail's foot are covered with scales that range up to 8
millimeters in length and overlap like roof tiles, says Anders Warén, a
marine biologist at the Swedish Museum of Natural History in Stockholm.
The core of those structures is made of a protein called conchiolin, a
common component of many mollusk shells. What makes these flaps unique
is their 100-micrometer-thick coating of iron sulfide, a biological
armor that's made of mineral particles just 1 µm in diameter. Bacteria living on the surfaces of the scales may contribute
to the formation of the mineral particles there. However, because the
tiny iron sulfide spheres also show up throughout the conchiolin core
of each scale, the snail itself probably controls the overall growth
and placement of the particles, says Warén. As snails are wont to do, these sulfide-armored creatures live
sedentary lives. This species doesn't even bother to eat. Instead, the
animals gain energy from symbiotic bacteria that live within the cells
of a gland in their esophagus, says Warén. Most mollusks have such
tissue, but in this armored species, the gland is about 100 times the
size of that found in related species. The bacteria harbored in the
gland oxidize dissolved sulfides that are absorbed through the snail's
gills, says Shana K. Goffredi, a marine biologist at the Monterey Bay
Aquarium Research Institute in Moss Landing, Calif. She, Warén, and
their colleagues describe the armored snail in the Nov. 7 Science.
The species is one of several creatures that make up the unique
ecosystems surrounding hydrothermal vents in the western reaches of the
Indian Ocean (SN: 9/15/01, p. 165: Available to subscribers at http://www.sciencenews.org/20010915/fob3.asp).
Although the researchers aren't sure about the function of the snail's
sulfide armor, it may provide protection from predatory snails. Those
killers inject their prey with poison, but their barbs aren't long
enough or tough enough to penetrate the mineral sheaths on the newfound
snail species, says Warén. David R. Lindberg of the University of California, Berkeley
rates the snail as "really interesting," but he doesn't buy the idea
that the mineral coating serves only as armor. There have to be other
advantages to the sulfide-coated scales, he says, because other species
of snails—ones that are just as common and presumably just as meaty and
delicious as their armored kin—thrive around the vents despite the
presence of predatory snails. ****************
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References: Warén, A., et al. 2003. A hot-vent gastropod with iron sulfide dermal sclerites. Science 302(Nov. 7):1007. Further Readings: Perkins, S. 2001. Scientists spy sixth undersea-vent ecology. Science News 160(Sept. 15):165. Available to subscribers at http://www.sciencenews.org/20010915/fob3.asp. Sources: Shana K. Goffredi
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA 95039
Anders Warén
Swedish Museum of Natural History
Box 50007
SE-10405 Stockholm
Sweden
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