ostracods introduction and morphology types

ostracods.pdf

2. Ostracods
Ostracods are small bivalved arthropods with chitinous or calcareous
valves that hinge at dorsal region of the body
They are known from more than 65, 000 living and extinct
species
Ostracods have adapted both benthic and pelagic lifestyle,
but most ostracods in the fossil record are benthic
Their fossil record extends back to the Cambrian
The earliest ostracods were completely benthic and occupied marine
shelf habitats.
Later, they also colonized pelagic environments during the Silurian and
also occupied terrestrial habitats during Carboniferous

3. Ostracods are widely used in biostratigraphy
They are used to determine palaeoenvironments
Benthic ostracods distribution have been
used to determine biogeographic provinces
10 zoogeographic ostracods
faunal provinces are
recognized from 10
o
S to 80
o
N

5. Ostracods soft body structure
The soft parts are sparsely
preserved in the fossil record
The head and thorax are fused
to form a cephalothorax

6. Ostracod limbs
Commonly have seven pairs of jointed limbs in the
adult stage but may have up to eight
ventral
dorsal
Limbs-basically biramous: divided in to two distinct
branches
Myodocopa-5 pairs of limbs arise from the head
while podocopa may have 4 pairs
walking
Walking, feeding and
swimming
Mastication of
food

7. Lack heart and larger blood vessels except few
larger planktonic myodocopes
Digestive and circulatory system are greatly
reduced
A pair of dorsal eyes whereas other benthic groups
have a single dorsal eye

8. The ostracod carapace
Ovate/kidney shaped or bean shaped
Hinge along the dorsal margin
Average size about 1-2 mm
The carapace is secreted by epidermis,
the duplicatures
Inner lamella
vestibulum

9. Inner lamella
vestibulum

10. Adont: Adont hinge is the simplest, lacking
teeth and sockets but provided with a single
groove along the margin of the larger valve and
a corresponding ridge on the smaller
Merodont: The merodont hinge has elongate
and crenulated terminal elements on the right
valve; the median elements may be smooth or
crenulated.
3. Amphiodont: The amphidont hinge has short
terminal elements that consist of well-
developed teeth on the right valve.
Dorsal hinge structures

11. Dimorphism:
Ostracods have well developed
reproductive system
Male and female are separate and secrete
carapaces of different sizes
Female- heteromorphs
Male- tecnomorphs

12. Ostracod reproduction and ontogeny
Ostracods reproduce sexually
Testes of the males produce
spermatozoa
Copulation with females results in
fertilization
Fertilized eggs are then either
brooded in the carapace, shed in to
the water or laid amongst water
weeds and stones
Ostracods grow in discontinuous
stages called instars
There are usually eight or nine instars
between the egg and adult stage
When the body grow the chitinous or
calcareous layer is moulted and a new
layer is formed

14. Morphology of the early instars and
adult is differents
Many parts such as thoracic limbs,
muscle scars and genital impressions
are progressively formed in different
instars
Due to this strong variation in
morphology at different stages,
taxonomic work is based on adult
specimens