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Composition,
origin and development of several groups of chitons which live
and feed on sunken wood
Twenty-three
species and subspecies of chitons living and feeding on sunken
wood are presently known. The group
includes members of three genera: Ferreiraella,
Nierstraszella and Leptochiton.
They live in deep waters from 150 to 7657m in different parts of
the Indian, Atlantic and Pacific Oceans. The length of digestive
tract of the xylophagous chitons is the same as in the detritic
feeders that confirm their closeness in feeding. Gut of most
these chitons contains mainly particles of sunken wood or leaves.
There are a lot of small white particles (size about 10μm)
besides particles of wood in the stomachs of these species.
Perhaps these white particles are cellulose-fermenting bacteria
or fungi. Their intestines and pellets contain particles of wood
or leaves only. The chitons which live on sunken wood and leaves
probably live at the expense of sunny energy which was
accumulated many years ago in cellulose of land plants. Taking
into consideration the existing of at least three groups of
chitons belonging to three different families and genera one can
suppose that food shifting has occurred several times
independently in different lineages. Probably the first species
which lived and fed on sunken land plants were species of the
Pennsylvanian genus Glaphurochiton
which were found in dark grey shales originated from muddy
grounds rich in organic remains.
Most of the species
which live on sunken land plants are distributed along the
tropical west and east coasts of Pacific Ocean and in the
Caribbean Sea which was one of the portions of the Pantalassa in
the past geological ages. All these species belong to the most
primitive families of chitons and show a lot of plesiomorphic
features. One can assume that the deep waters off South Japan,
Philippines, Indonesia New Caledonia, Vanuatu, New Zealand from
the west part of Pacific and of Baja California, Panama Basin
from east Pacific as well as the Caribbean Sea are the
regions where species with primitive characters have
accumulated and conserved during long geological period. In
future one would expect a number of other such primitive species
will be found in the deep waters of these areas which are the
most ancient areas of the Pantalassa remaining to present time.
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