OSTRACODA

DISTRIBUTION AND ECOLOGY OF OSTRACODS

Ostracods are: 1- pelagic (planktonic) by using organic-walled shell (less

Ca CO3) or by producing oil droplets. Pelagic ostracods

are not preserved in the sediments.

2- benthic on/in the sea floor. They can burrow, swim

near the sea-bed or crawling on or through the sediment.

Benthic forms occur in all the aquatic environments from the

abyss to the shoreline. They also occur in estuaries, lagoons,

freshwater lakes, ponds and streams, salt lakes, hot springs,

damp vegetation.

Lecture Two

cold, deep waters 500 m, temperature around 4 to 6° C.

Large > 1 mm in length-Animals is blind (eye tubercles are missing).

Ornamentation is so dense.

Benthic ostracods divided into two major groups:

Thermospheric ostracodsPsychrospheric ostracods (bathyal and abyssal)

Thermospheric ostracods Shallow waters under

less-dense, warm ( > 10° C) waters

Small Eye present. More diverse than the

psychospheric ostracods

Cyprideis torosaLegitimocythere

Ostracods can be influenced ecologically by various factors such as:

1. Type of the substrate:- Swimmers have smooth, thin, bean-shaped carapace.- Fine-grained (mud) dwellers have flattened ventral, wing-shaped carapace.- Coarse-grained (sand) dwellers have thick carapace with coarse ornamentation.- Interstitial ostracods are small, long and robust.

2. SalinityOstracods carapace morphology tend to vary according to variation in salinity. They occur in fresh water (0.0-0.5‰) of rivers and estuaries, brackish water (0.5-30‰) of lagoons and marshes, normal sea water (35-45‰) and hypersaline water bodies (up to 57‰) of the closed seas, lakes, lagoons and marginal bays.

Ecological variables

3. Depth:Populations of living pelagic forms increase with increasing the water-depth, whereas benthic forms show highest diversity near shallow waters.

Psychospheric forms occur around 500 m depth.

Thermospheric forms is restricted to the photic zone (0.0-

150 m).

4. Temperature:

Latitudinal temperature controls the shallow water forms.

At tropical regions, faunas are more abundant and diverse

than at the higher latitudes.

Applications of ostracods

Occur in the sedimentary column since the Early Ordovician, so they can be used as:

1- stratigraphic markers.

2- Paleo-salinity indicators

3- Paleo-depth indicators

Changes in the proportions of fresh- and brackish-water ostracoda with inferred salinity changes, from part of the Lower Headon Beds (Modified from Keen, 1977).

CLASSIFICATION

Based on: general shape, valves overlapping, presence of ornamentation, hige characteristics and male and female structures. Ostracoda divided generally into five main orders:

Order: Archaeocopida

Order: Leperditicopida

Order: PodocopidaSuperfamily: BairdiaceaSuperfamily: CypridaceaSuperfamily: CytheraceaSuperfamily: Darwinulacea

Order: Myodocopida

Order: Palaeocopida

Orders Archaeocopida and Leperditicopida: a) Bradorai, b) Indiana, c) structure features of leperditicopida and d) Leperditia. From Brasier, 1980.

Order Podocopida (superfamily Bairdiacea): a-c) Bairdia. From Brasier (1980).

Order Podocopida (superfamily Cypridacea): a) Cypris, b) details of Paracypris, c) Carbonita, d) Cypridea and Argilloecia. From Brasier (1980).

Order Podocopida (superfamily Cytheracea): a) Limnocythere, b) Cytheracean muscle scar, c) Cyprideis and d) Cytherura. From Brasier (1980).

Order Podocopida (superfamily Darwinulacea): a-c) Darwinula sp. From Brasier (1980).

Order Myodocopida: a) Richteria, b) Entomoconchus, c) Thaumatocypris and d) exterior LV of Jurassic species. From Brasier (1980).

Order Palaeocopida: a-b) Beyrichia, c) Hollinella, d) Aechmina and e) Oepikium. From Brasier (1980).

HISTORY OF OSTRACODA

(Stratigraphic position)

Diversity of ostracod taxa through time. Width of bars corresponds to the number of genera, from Brazier (1980).