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Chitons, commonly referred to as Coat of Mail shells
or Sea Cradles, are a relatively small marine mollusc easily
recognized by eight overlapping armor plates (valves)
surrounded and held together by a leathery girdle or
mantle. Small nodules of the mineral aragonite embedded
in the shell provide a lens through which the aesthetes
(unique light sensitive cells) lying below can detect light,
movement and possibly even discern shapes. The chiton
essentially “sees” through these opaque rocks in its shell,
visual equipment unlike that of almost any other creature.
The girdle is often ornamented with hairy tufts, bristles,
spikes or scales that provide camouflage and may
also aid in defence. In some species including the largest
(the Gumboot Chiton or Wandering Meatloaf), the mantle
actually covers the entire shell.
The armor plates themselves are articulated and can
flex and move over each other, offering both protection
and freedom of movement over the jagged intertidal
rocks on which they choose to make their home. When
a chiton dies, the girdle decomposes and the individual
plates fall apart. These may be discovered by keen-eyed
beachcombers and are referred to as Butterfly Shells.
Most chitons are herbivorous grazers, roaming the
rocks under cover of darkness, feeding on encrusting
algae by scraping it into their mouth with a tooth-covered
tongue called a radula (from the Latin radere “to scrape”).
There are, however, some carniverous chitons, competing
with all the suspense and horror of a good Ridley Scott
movie. The predatory species Placiphorella velata waits
patiently in ambush, its body held aloft. Smaller animals
seeking shelter and shade under this murderous cave
are crushed to death and consumed should they inadvertently
touch the sensitive tentacles below and spring the
deadly trap above.
The chiton’s teeth are of significant interest to science
as their microscopic structure and composition—a
matrix of organic tissue and inorganic minerals—makes
the teeth incredibly wear-resistant, allowing the chiton to
nonchalantly chew through rock. A chiton literally makes
its home (scar) in the rock by eating the rock away. The
teeth contain magnetite or iron (II, III) oxide, a crystal
compound that is also found in the beaks of homing
pigeons and is the most magnetic of all the natural minerals.
These highly magnetic inorganic teeth are found
nowhere else in the animal kingdom and may explain the
chiton’s remarkable homing ability, after a night of foraging,
to use the Earth’s magnetic field to navigate back
to precisely the same home scar in the rock.
Their taxonomic class name is Polyplachophora
(many plated). Unlike most molluscs, conch for example,
chitons cannot withdraw back into their shell. Instead
they use their very powerful, muscular foot to cling to
the rocks like a limpet and are almost impossible to prise
off. When dislodged from the substrate, the chiton can
roll up into a protective ball, like a tiny marine armadillo.
The chitons’ main predators are man (naturally),
seagulls, starfish, crabs, lobsters and fish. Chitons
are eaten in several parts of the world including the
Caribbean islands of Trinidad, Tobago, The Bahamas,
Aruba, Anguilla, Bonaire, St. Maarten and Barbados. The
foot of the chiton is prepared in a manner similar to abalone.
They don’t seem to be on the menu in the Turks &
Caicos though, conch being the much-preferred option.
Next time you look into a rock pool you may see a
little armored snail, present from the dawn of time with
magnetic teeth that can pulverize rock with its tongue
and see through eyes of made of stone—an amazing little
animal that you probably didn’t even know was there. a
A native of Ireland, Brian moved to the Turks & Caicos
with his wife Sabine in 2016 where they opened The
Humpback Dive Shack on Grand Turk.
Times of the Islands Spring 2020 29