Geoscience Reference
In-Depth Information
98
animals might have looked in life ( 98 ).
Trigonotarbids have a tough carapace with
projections between the leg bases. There
are two clusters of eyes, each consisting of
three major lenses and several minor ones
between, and a pair of median ocelli. The
eye clusters show an evolutionary stage
between compound eyes with many, similar-
sized lenses, and the condition in spiders
(which have three major eyes in each lateral
group plus the median ocelli = eight
altogether). The first pair of appendages is
the chelicerae: little pincers, as found in all
chelicerates (see Chapter 5); all other
appendages on the prosoma are leg-like.
The opisthosoma, or abdomen, is covered
with hard plates, presumably for protection
from predators. Several genera and species
of trigonotarbid were described from
Brown Mountain (Shear et al ., 1987), and
others have been found elsewhere in the
Devonian of the Catskills, e.g. South
Mountain, and in the late Devonian of
Pennsylvania (Shear, 2000).
Spiders
Shortly after the description of the
trigonotarbids from Brown Mountain, a
fragment of cuticle was discovered which
bore silk-producing spigots ( 99 ), and thus
98 Tiny, juvenile trigonotarbid Gelasinotarbus
bonamoae, nearly complete in two parts
AMNH. Body length 1.5 mm 0.06 in.
99
99 Piece of cuticle of the
spider Attercopus fimbriunguis
bearing characterictic silk-
producing spigots. Note the
bell-shaped bases of the spigots
which are derived from
modified setae; ordinary setae
in follicles; and tiny, elongate
slit sense organs PC. Width of
slide 0.25 mm 0.01 in.
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