| abathochroal |
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. |
| abaxial |
away from the axis (center line) |
| adaxial |
toward the axis (center line). |
| anamorphic |
a mode of development in which each molt results in addition of one or few segments. see epimorphic, hemianamorphic. |
| articulation |
separation of two rigid tergites (rigid dorsal units) by a flexible joint. |
| articulating facets |
see facets. |
| axial |
pertaining to the axis. |
| axis |
central lobe running the
length of the trilobite body; the glabella is the main expression
of the cephalic axis. |
| cephalic |
pertaining to the cephalon. |
| cephalon |
frontmost trilobite tagma (functional set of segments);
head. |
| cheek |
see gena. |
| coaptation |
close interlocking of opposing surface during enrollment |
| conterminant |
hypostome attached
to anterior doublure via suture. see impendent, natant. |
| dorsal |
referring to the top or
back surface, as opposed to ventral (underside). |
| doublure |
shell continuation under
the trilobite, typically as a ventral cephalic, thoracic, and/or pygidial
rim. |
| effacement |
loss of detail; effacement is an evolutionary trend in trilobites. |
| enrollment |
bending of the body to enclose vulnerable ventral
organs in a protective clam-like or sphereoid capsule formed by the cephalon,
pygidium and thoracic segments. |
| epimorphic |
a mode of development in which molts are not accompanied by segment addition. see anamorphic, hemianamorphic. |
| facets |
flat surfaces, typically
where two adjoining body parts meet and articulate (move); e.g., articulating
facets on thoracic pleural segments. |
| fixigena |
"fixed cheek" cephalic
shell surrounding glabella inside of facial sutures. see gena,
librigena. |
| fulcrate |
referring to thoracic
segments with a geniculation (bend) separating a horizontal adaxial portion
from an inclined abaxial portion. |
| furrow |
linear groove, often defining adjacent convex features, such as lobes of the glabella |
| gena (pl.,
genae) |
shell
of the cephalon surrounding the glabella, (also called cheeks) usually divided
by sutures into fixigena (fixed cheek) and librigena (free cheek). |
| genal angle |
angle formed by the meeting
of the lateral (side) and posterior (rear) margins of the cephalon;
sometimes expressed as a genal spine. |
| genal spine |
a spine anywhere on the
gena (cheek) of the cephalon, typically at the genal
angle, but see metagenal spine, progenal spine. |
| glabella |
middle (axial) portion
of cephalon, typically convex and lobed. |
| gonatoparian |
facial sutures
ending at the tip of the genal angle. |
| granulate |
bearing granules or similar
sculpturing (prosopon) on the outer exoskeleton. |
| hemianamorphic |
typical mode of development in trilobites, in which early stages (protaspis, meraspis) show anamorphic development, while later development (holaspis) is epimorphic. |
| holaspis |
final developmental stages
beyond meraspis, attaining a certain number of thoracic segments
considered typical of "adult" individuals, and with cephalic
and pygidial characters of adult. |
| holochroal |
eyes with adjacent compound lenses
directly in contact, all covered by a single continuous smooth corneal surface.
see abathochroal, schizochroal. |
| hypertrophy |
grown well beyond normal
size. |
| hypostomal |
pertaining to the hypostome. |
| hypostome |
a piece of exoskeleton
on the venter (underside) of the cephalon, thought of as a mouthpart.
Typically the anterior edge of the hypostome lies directly under the anterior
edge of the glabella. |
| impendent |
type of conterminent
hypostomal attachment, but doublure underlies anterior glabellar
edge, so anterior hypostomal border does not match anterior glabellar border.
see conterminant, natant. |
| isopygous |
cephalon and pygidium
similar in size. see micropygous, macropygous. |
| konservat-lagerstatten |
special category of fossil deposits (fossil-lagerstätten)
where soft tissue features have been conserved particularly well (as in the
Burgess Shales). see lagerstätten. |
| lagerstätten |
geological deposit, especially fossil-lagerstätten
(fossil beds), konzentrat-lagerstätten (concentrations of fossil parts)
and konservat-lagerstätten (fossil beds with remarkably conserved soft
body detail - see above) |
| librigena |
"free cheek" cephalic
shell to the right and left of the glabella outside of facial sutures,
often lost during molting or after death. see fixigena, gena. |
| macropygous |
pygidium larger
than cephalon. see isopygous, micropygous. |
| meraspis |
developmental stage following
protaspis, bearing more than one segment, but with fewer than
adult number of thoracic segments. see protaspis, holaspis. |
| metagenal spine |
genal spine originating along the posterior margin of the cephalon, adaxial of the genal angle, called metafixigenal if it springs from the fixigena, or metalibrigenal if from the librigena. |
| micropygous |
pygidium much smaller
than cephalon. see isopygous, macropygous. |
| natant |
hypostome free,
not attached to the cephalic doublure. |
| occipital |
pertaining to the occiput. |
| occiput |
posterior portion of cephalon,
the axial portion is considered part of the glabella (occipital
ring). |
| opisthoparian |
facial sutures
ending along the rear margin of the cephalon adaxial to the
genal angle. see gonatoparian, proparian. |
| opisthothorax |
posterior, narrower portion
of thorax when it is divided into wider, anterior prothorax
and opisthothorax. |
| palpebral |
portion of fixigena
associated with the eye. |
| perrostral |
along the edge of the
rostrum. |
| pleura (pl., pleurae) |
lateral (side) part of thoracic segment or lateral (non axial) part of pygidium. |
| pleural |
referring to pleurae. |
| postaxial |
extending from the end
of the axis. (e.g., a postaxial spine.) |
| preglabellar field |
portion of cephalon
in front of glabella. |
| progenal spine |
genal spine originating anywhere along the margin of the cephalon, anterior of the genal angle, called profixigenal if it springs from the fixigena, or prolibrigenal if from the librigena. |
| proparian |
facial sutures
ending forward of the genal angle. |
| prosopon |
exoskeletal sculpturing, including pits, ridges, furrows, granules, tubercles, and small spines. |
| protaspis |
developmental stage lacking
articulated segments. see meraspis, holaspis. |
| prothorax |
anterior and wider portion
of thorax when it is divided into prothorax and narrower, posterior opisthothorax,
as seen in some Redlichiida. |
| pygidial |
pertaining to the pygidium. |
| pygidium |
hindmost body section
(tagma) composed of fused segments; tail, separated from thoracic segments
by an articulation. |
| pyriform |
pear-shaped, typically referring
to the glabella |
| rostral plate (rostrum) |
middle portion of the
ventral cephalic doublure, typically where the hypostome
attaches in conterminant or impendent trilobites. |
| schizochroal |
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. |
| spinose |
bearing a spine or
spines. |
| sternite |
ventral
exoskeleton unit, not calcified in trilobites, separated from
other such units by sutures or unsclerotized membrane, typically axial. |
| subisopygous |
pygidium large,
but not quite as large as cephalon. |
| subparallel |
nearly parallel in
arrangement, slightly diverging or converging. |
| suture |
linear break in exoskeleton,
typically along which parts separate during molting. |
| tagma (pl. tagmata) |
grouping of segments that form a functional unit. cephalon, thorax, & pygidium are trilobite tagmata. |
| tergite |
a rigid dorsal exoskeletal unit, calcified in trilobites, composed of either single segments (e.g., individual thoracic segments) or fused segments (e.g., the pygidium) separated from other such units by articulations (e.g., thoracic tergites) or sutures (e.g., cephalic genae). |
terrace ridge
|
linear assymetrical ridges running subparallel to
the margin on the outer portion of pleural region, border, doublure,
and hypostomes of some trilobites; a type of prosopon.
|
| thorax |
middle, segmented body
portion between cephalon and pygidium. see prothorax,
opisthothorax |
| thoracic |
pertaining to the thorax. |
| tuberculate |
bearing tubercles or similar
sculpturing on the outer exoskeleton. See prosopon. |
| ventral |
referring to the underside. |
| vincular 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 Phacopida). |
