OSTRACODA
Lecture Two
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.
Benthic ostracods divided into two major groups:
Psychrospheric ostracods
(bathyal and abyssal)
cold, deep waters  500
m, temperature around 4
to 6° C.
Large > 1 mm in lengthAnimals is blind (eye
tubercles are missing).
Ornamentation is so
dense.
Legitimocythere
Thermospheric ostracods
Thermospheric ostracods
Shallow waters under
less-dense, warm ( > 10° C)
waters
Small
Eye present.
More diverse than the
psychospheric ostracods
Cyprideis torosa
Ecological variables
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. Salinity
Ostracods 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.
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 (0.0150 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: Podocopida
Superfamily: Bairdiacea
Superfamily: Cypridacea
Superfamily: Cytheracea
Superfamily: 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).