Phylum Arthropoda
CLASS CRUSTACEA (SUBCLASS OSTRACODA)
MORPHOLOGY
Images taken from Howe, Kelsing, and Scott ,1961 and Scott, 1961
Some very basic ostracode morphology can be seen in the two images below. The image on the left shows the internal anatomy of a Recent ostracode. The image on the right displays some simple external features that may be present on the valves.
TERMINOLOGY
Definitions of terms taken from Moore, 1961
Adductor muscle scar -Impression on valve interior of muscle serving for closure of valves, generally located in front of mid-length.
Border (or margin) – Periphery of carapace or valve as seen in lateral view.
Carapace – Protective covering of ostracode soft parts, including appendages, forming two nearly symmetrical valves joined together by hinge along dorsal border; mostly hard calcareous but soft and uncalcified in most Archeocopida and many Myodocopida.
Contact margin – Edge part of valves exclusive of hinge, in contact when valves are closed, its distal limit comprising free edge.
Equivalved - Valves having the same size and shape.
Denticulate - Bearing a series of small spinelike or toothlike projections.
Free edge – Line of contact between closed valves except along hinge line; marks distal limit of contact margin and may lie inside free margin.
Free Margin – Anterior, ventral, and posterior parts of border where valves are not held together by hingement.
Furrow – Shallow groove on valve surface.
Granulose – Surface ornamentation of valves consisting of more or less closely spaced minute protuberances, generally without distinct pattern, like grains of sandpaper.
Hinge - Part of valves along or near dorsal border serving for articulation.
Hinge line – Line along which valves articulate, seen when carapace is complete; it may coincide with dorsal border or be depressed below it.
Lobe – Rounded major protuberance of valve surface, generally best developed in dorsal part of carapace; also used for part of hinge tooth (projection of hinge area aiding in articulation of valves).
Margin – See border.
Nonsulcate - Valve surface evenly elevated, unilobate, lacking sulcus.
Node – Protuberance of intermediate size on valve surface, clearly distinct from lobes.
Punctate – Surface bearing many minute depressions resembling pin pricks.
Sulcus – More or less prominent groove or trench on valve surface trending dorsoventrally and generally best developed in dorsal half of carapace; in some genera may be reduced to faint depression.
Trisulcate – Valves having three sulci (S1 S2 S3) and four lobes.
Valve – One of the two halves of carapace, hinged at upper (dorsal) edge, classed as left valve and right valve.
CLASS TRILOBITA
MORPHOLOGY
These two images are labeled with some of the basic morphology of the trilobite exoskeleton. The diagram to the left is based on an Isotelus gigas specimen and to the right, a Ceraurus pleurexanthemus specimen. Both are found in the Trenton Group at West Canada Creek.
TERMINOLOGY
Definitions of terms taken from Whittington and Kelly, 1997
Axial furrow – Groove on external surface formed by fold in exoskeleton that outlines the axial region of cephalon, thorax, and pygidium.
Axial lobe – Median region of dorsal exoskeleton, bordered by axial furrow including preglabellar furrow.
Axial ring – Central portion of thoracic segment or of a segment of pygidium, bounded laterally by axial furrow. May be subdivided by intra-annular furrow into preannulus and postannulus.
Border - Outer dorsal portion of cephalon and pygidium and outer ventral portion of hypostome, usually bounded by border furrow (has been referred to as rim, marginal rim, or marginal limb, but the term rim is restricted here to narrow peripheral ridge of fringe of Trinucleidae, etc.).
Border furrow – Furrow defining adaxially border of cephalon, pygidium, and hypostome (syn., marginal furrow).
Cephalon (pl., cephala) – Anterior tagma composed in trilobites of a number of fused somites ( transverse division of arthropod body), applied by authors to anterior portion of exoskeleton separated from remainder of exoskeleton by an articulation (syn., cephalic region, head, head shield).
Cranidium (pl., cranidia) – Central portion of exoskeleton of cephalon, bounded laterally by facial suture.
Dorsal shield – Mineralized dorsal cuticle extended onto ventral side as doublure and hypostome.
Doublure – Reflexed continuation of dorsal exoskeleton onto ventral surface.
Facial suture – Suture bounding adaxial margin of eye surface, which had anterior and posterior branches (sections), each of which may extend over the border and on to the doublure; suture separates free cheek from fixed cheek. Posterior branch extends to inner margin of doublure, anterior branches may meet medially on dorsal or ventral surface of exoskeleton or may join extremity of rostral suture. Facial suture may be present when eye is absent.
Fixed cheek – Portion of cranidium abaxial to axial and preglabellar furrows and imaginary sagittal line bisecting frontal area.
Free cheek – Portion of cephalon abaxial to facial suture.
Genal angle – Posterolateral corner of cephalon.
Genal spine – General term for hollow, posteriorly directed extension of border and doublure at genal angle, forming pointed projection.
Glabella – Axial portion of cephalon, bounded by axial and preglabellar furrows.
Granule – Minute protuberance from exterior surface of exoskeleton, smaller than tubercle or pustule.
Holaspid (holaspid period) – Period of growth after specific number of thoracic segments had been attained.
Holocroal eye – Compound eye consisting of numerous adjoining lenses covered by a continuous cornea.
Hypostome – Ventral sclerite (portion divided by an articulation or by a suture) situated beneath anterior portion of glabella.
Interpleural furrow – Transverse groove extending from axial furrow across pleural region of pygidium, indicating boundary of fused pleurae (syn., interpleural groove, rib furrow).
Lateral glabellar furrow – Bilaterally symmetrical pairs of narrow grooves on external surface formed by fold in exoskeleton, extending partway across glabella from (or near) axial furrow. Furrows vary in length, depth and direction; they may be short, limited to pits in or close to axial furrow, or isolated from axial furrow. When three pairs are present, they have been referred to as anterior, median, and basal (syn., posterior glabellar furrow, preoccipital glabellar furrow). Numbering from the back forward is preferred: occipital as S0, preoccipital as S1, and continued forward as S2, S3, etc.
Lateral glabellar lobe – Portion of glabella outlined and more or less separated by successive lateral glabellar furrows, may or may not be inflated. Numbering is from posterior end forward: L1, L2, etc. In lichids it is considered that L1 is subdivided into posterior L1a and anterior L1b, and similar subdivisions are recognized in odontopleurids. When three pairs are present they have been referred to as anterior, median, and basal lobes.
Lunette – Raised cresentic area on inner (parietal) surface of exoskeleton at abaxial margin of axial furrow, where glabella is narrowest and approximately in transeverse line with eye lobe; characteristic of Illaenidae.
Margin (frontal/posterior) – Distal edge of portion of exoskeleton.
Occipital furrow – Transverse furrow (S0) that isolates occipital ring from remainder of glabella.
Occipital ring – Axial region of most posterior segment of cephalon, bounded at sides by axial furrows, at front by occipital furrow, and at back by posterior margin. Considered part of glabella in all trilobites.
Ontogeny - The growth cycle.
Palpebral lobe – Protruding subsemicircular flange of fixed cheek bounded distally by palpebral suture (portion of facial suture bounding distal edge of palpebral lobe). Forms with the visual surface of the eye to form the eye lobe.
Pleural furrow – Groove in external surface of thoracic pleuron or pleural region of pygidium, formed by fold in exoskeleton.
Pleural lobe – Lateral portion of thorax or pygidium abaxial to axial furrow.
Pleuron ( pl., pleurae) – Lateral portion of thoracic segment.
Preglabellar furrow – Portion of axial furrow outlining front of glabella.
Pustule – Small, rounded elevation on any part of external surface of axoskeleton. See tubercle.
Pygidium (pl., pygidia) – Posterior tagma in trilobites, composed of fused somites (transverse division of arthropod body), applied by authors to posterior portion of the exoskeleton separated from the thorax by articulation.
Schizocroal eye – Eye with visual surface consisting of number of biconvex lenses, rounded or polygonal in outline, each lens covered by individual cornea and separated from others by sclerotic walls.
Subquadrate – Nearly or approximately square.
Thorax – Region of trilobite body between cephalon and pygidium in which successive somites (transverse division of arthropod body) are articulated; also used to refer to exoskeleton region, the segments of the thorax.
Tubercle – Small, knoblike prominence on external surface. See pustule.