eyes: eyes with compound
lenses, each with separate cornea, each lens separated from
others by shallow scleral walls; corneal membrane ends at lens
edge. see holochroal, schizochroal.
central lobe running the length of the trilobite body
The appendages of arthropods may be either biramous or uniramous.
A biramous limb, however, branches into two, and each branch
consists of a series of segments attached end-to-end. Also see
the frontmost trilobite part, i.e., the head.
(C8H13O5)n is a long-chain polymeric polysaccharides of beta-glucose
that forms a hard, semitransparent material and found as a component
of many arthropod exeskeletons.
close interlocking of opposing surface during enrollment
a condition where the hypostome is attached to the anterior
doublure with a suture. Other trilobite hypostome conditions
are impendent and natant.
referring to the top or back surface, as opposed to ventral.
shell continuation under the trilobite, typically as a ventral
cephalic and/or pygidial rim.
loss of detail.
the bending of the trilobite body, especially to enclose vulnerable
ventral organs in a protective wrapper formed by the dorsal
exoskeleton of the cephalon, pygidium and thoracic segments.
adjacent flat surfaces, normally where two adjoining body parts
contact and can articulate (i.e, where they are hinged); e.g.,
the articulating facets on thoraxic pleural segments.
the fixed cheek cephalic shell surrounding
glabella inside of facial sutures. Also
seee gena and librigena.
referring to thoraxic segments with a geniculation (bend) separating
a horizontal inner portion from an inclined outer portion.
the shell of the cephalon surrounding the glabella that is normally
divided by sutures into the fixigena and the librigena.
angle: the angle formed by
the meeting of the lateral (side) and posterior (rear) margins
of the cephalon; the angle is important in trilobite taxonomy.
spine: a spine anywhere on
the gena (i.e., cheek) of the cephalon, typically pointing at
the genal angle.
that middle (axial) portion of cephalon
that is typically convex and/or lobed.
a condition where the facial sutures end at the tip of the genal
granules or granule-like features on the exoskeleton.
the final trilobite development stage following the meraspis
stage; the trilobite successively adds thoraxic segments until
the number is reached correcponding to that of adults The cephalic
and pygidial features of the adult are also attained.
a type of trilobite eye having all the compound lenses directly
in contact, and all covered by a single, continuous corneal
surface. Holochroal eyes were usually high in number (15,000
and more), and have been found in all nine of the trilobite
orders. A hexagonal shape enabled tight packing (much like a
graphite crystal). These eyes had no sclera. - also see abathochroal,
schizochroal, the other types of trilobite eyes.
a condition of growth nominal size.
adjective meaning related to the hypostome.
a portion of the exoskeleton underneath the cephalon, thought
to be a mouthpart in trilobites. Typically, the anterior edge
of the hypostome is directly under the anterior edge of the
a type of conterminent hypostomal attachment where the doublure
underlies the anterior glabellar edge, such that the anterior
hypostomal border does not match the anterior glabellar border.
Contrast with conterminant and natant.
a condition where the trilobite's cephalon
and pygidium have similar size and possible symmetry. Contrast
with micropygous and macropygous.
a place of extraordinary fossil preservation, often including
mineralization of soft tissues.
the so-called free cheek of the cephalic
shell on either side of the glabella
outside of the facial sutures. They are often lost during ecdysis
(moulting) or after death. see fixigena, gena.
a trait of the pygidium being larger than the cephalon contrast
with isopygous and micropygous.
the trilobite developmental stage following the protaspis stage
where the trilobite has more than one thoraxic segment, but
fewer than the adult number of an adult. Aso see protaspis and
a morphological condition where the pygidium much smaller than
cephalon. Also see isopygous and macropygous.
hypostome free, not attached to the cephalic doublure.
related to the to the trilobite occiput.
the posterior portion of trilobite cephalon, where the axial
portion is considered part of the glabella , i.e., the occipital
the facial sutures terminating along the rear margin of the
trilobite cephalon adaxial to the genal angle. Also see gonatoparian
the posterior, narrower portion of the trilobtes thorax when
it is divided into wider, anterior prothorax and opisthothorax.
that portion of trilobite fixigena associated with the eye.
along the edge of the rostrum.
(pl., pleurae) lateral (side) part of thoraxic segment or lateral
(non axial) part of pygidium.
referring to pleurae.
extending from the end of the axis.
field: portion of cephalon in front of glabella.
facial sutures ending forward of the genal angle.
developmental stage lacking segments. Also see meraspis and
anterior and wider portion of thorax when it is divided into
prothorax and narrower, posterior opisthothorax, as seen in
pertaining to the pygidium.
hindmost segment; tail.
pear-shaped, typically referring to the glabella
plate: (rostrum) middle portion of the ventral cephalic
doublure, typically where the hypostome attaches.
eyes: with compound lenses, each with separate cornea,
each lens separated from others by deep scleral walls; corneal
membrane extends downward into sclera. see abathochroal, holochroal.
(plural setae): a stiff hair, bristle, or bristle-like process
or part of an organism often used to cling to surfaces or gain
bearing a spine or spines.
pygidium large, but not quite as large as cephalon.
nearly parallel in arrangement, slightly diverging or converging.
linear break in exoskeleton, typically along which parts separate
(plural terga) the dorsal portion of an arthropod segment other
than the head. The anterior edge is called the base and posterior
edge is called the apex or margin. A tergum can be divided into
several plates, called tergites. In a thoracic segment, the
tergum may be divided into an anterior notum and a posterior
scutellum. In crustaceans, it is known as a pleuron when it
overhangs the insertion of the limb on each side as a free plate.
The ventral portion of a segment is called the sternum.
middle, segmented body portion between cephalon and pygidium.
see prothorax, opisthothorax
thoracic pertaining to the thorax.
bearing tubercles or similar sculpturing on the outer exoskeleton.
the appendages of arthropods may be either biramous or uniramous.
A uniramous limb comprises a single series of segments attached
end-to-end. For a time, possession of uniramous limbs was believed
to be a shared, derived character, so uniramous arthropods were
grouped into a taxon called Uniramia. It is now believed that
several groups of arthropods independently evolved uniramous
limbs from ancestors with biramous limbs, so this taxon is no
longer used. Also see biramous.
referring to the underside.
furrow: a groove along the anterior and/or lateral
cephalic doublure to accommodate the edge of the pygidium and
thoracic pleurae during enrollment (e.g., a feature of some