SEMINAR ON
MORPHOLOGY OF
OSTRACODS
SUBMITTED TO SUBMITTED
BY
DR.S.R.JAKHAR DEVESHWAR
MISHRA
M.SC II SEM.
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descibed paleontology related mophological features in fossils
Typology: Study notes
2016/2017
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SEMINAR ON
MORPHOLOGY OF
OSTRACODS
SUBMITTED TO SUBMITTED
BY
DR.S.R.JAKHAR DEVESHWAR
MISHRA
Kingdom : Animalia
Phylum :
Arthropoda Subphylum :
Crustacea
Class : Ostracoda
Ostracoda
The term “carinal structure” was proposed by Jaanusson (1957) foe different kinds of nondimorphic ornamental ridges situated lateroventrally and often occupying about the same position as the connecting lobe in quadrilobate valves. Velate structure are common in the Paleocopida and previously have been applied only to this group though velate like structure occur in Cythereis, Pterygocythereis, kingmaina and other Mesozoic and Cenozoic genera.
Lateral Surface
The lateral surface of ostracodes valves can be divided inti posterior and anterior portions and into dorsal and ventral portions. The dividing line between anterior and posterior is placed at mid- length and between dorsal and ventral at mid- height. The lateral surface of ostracodes valves may be smooth or highly ornamented by granules, postules, striae, sostae, pits, spines or reticula. Granules may be closely packed or sparsely distributed over part or all of the surface. Straie are fine furrows separated by very minute ridges.
The presence of all lobes indicates quadrilobate valve, a trilobate valve bears lobes designated as L1, L2 and L3, a trilobate valve has only L1 and L2.
Sulci are elongate depressions of the domicilium labelled S1, S2 and S3. Sulci are expressed internally by corresponding elevations. A typical sulcus opens dorsally and may open at both ends.
In some forms all of the lobes merge ventrally into a ventral lobe. This is well illustrated in Tetradella marchia.
Unisulcate, Eukloedenella, bisulcate Kloedenella and trisulcate Dizygopleura are all closely related genera.
The number and character of Sulci and Lobes cannot be used generally form familial differentiation; they are aids to classification on all levels but are not be themselves genarally definitive in any category other than species.
DORSAL AREA The general outline, nature of the hinge contact from of lobation and sulcation and presence of dorsal carinal are features that may be observed in dorsal view. The hinge line may be depressed in a channel, comprise the highest most dorsal edge of the carapace. The exterior terminations of the hinge fall into four general classes:- (a)Without cardinal angles and hinge contact not directly exposed (e.g- Cytherella, Bairdia) (b)With cardinal angles with developed, hinge ,line straight and uninterrupted by teeth or overlap, no channel (e.g- Ctenobolbina, Primitia)
Muscle Scars:- Muscle scars are very important shell features that commonly are preserved in Mesozoic and Cenozoic forms but less so in Paleozoic ostracodes. The presence of scars often has been over looked bacause of the apparent opaquences of the shell. The best known scars in Paleozoic ostracodes are found in the Laperditiidae. The large adductor scar is composed of as many as 100 small secondary scars. Only a few scars of myodocopida have been
Internal Features
In the platycopines the adductor muscle scar is composed of a closely spaced set of secondary scars arranged in a double row. The secondary scars was usually 10 to 14 in number.
Scars in some of the metacopine podocopids are well known, in others
unknown. The large number of secondary
scars in Cavellina clearly shows that such
a form can not be classified with an ostracode like Cytherella. In the Bairdiacea seven or more
secondary scars are closely packed into a
subcircular group, very closely packed in
Hingement
Hingement is one of the most important features for use in classifying Mesozoic and Cenozoic ostracods. Hinge characters are not so well known among the Palaeocopids but are used wherever possible. The two valves of an ostracode are articulated in a variety of ways along the dorsal margin. Types of hingement may be divided into four broad groups- (A)Smooth contact without interlocking devices (B)Straight or curved, smooth or denticulate hinge bar (C)Straight or curved hinge bar and groove supplemented by cardinal teeth and sockets which are smooth or partially to wholly crenulate (D)A peripheral lock in genera in which one valve is larger than the other.
- Merodont hingement consists of a bar terminated by crenulate teeth in one valve opposed to a groove and sockets in the opposite valve. Four varieties are known and all are believed to be a development of adont or prinodont structures.
- In Entomodont hingement four elements are distinguished; a medium bar with (A) a coarsly crenulated anterior element (B)smooth or crenuate remaining portion (C) anterior (D) posterior crenulate teeth