Ostracoda Flashcards
Name Ostracod key characteristics
- 7 pairs of legs (antennules, antennae, mandible, maxilla and 3 pairs of walking limbs)
- Dimorphic as adults, expressed in carapace
- Brood their young
- Benthic and pelagic forms
- pelagic forms have thin shells butstrong swimming appendages, compound eyes and advanced circulatory system
Name the 3 main anatomical features of an ostracod carapace:
- bivalved calcite carapace
- have to moult the carapace as they grow
- carapace is hinged dorsally
Is there evidence of ostracoda in the Cambrian?
Phosphate carapaces have been found that look like them but cant prove it without soft parts, in the Chengjiang they found some with more than 7 limbs therefore not Ostracods, they are Braderida!
In shropshire they discovered phosphatocopids which arent ostracods but Tom Harvey found one ostracod mandible?
Conclusion: NO
What are Leperditicopids?
They look like ostracods and favoured shallow marine lagoons but are too big! (can’t find any soft parts either)
Name the different types of hinge:
- Adont (flat/smooth)
- Merodont (some overlap possibly some roughness)
- Amphidont (very rough strong overlap)
Podocope limbs are…
biramous (with inner and outer branches)
How are mydocopia adapted to pelagic life?
- They have strong muscles and powerful second antennae that extend from the rostral notch
- calcite shell is smooth, thin and light
Describe mydocopia courtship behaviour:
Males of some species attract females using bio-luminescence, each species has its own pattern
How do mydocopia produce bio-luminescent chemicals
Chemicals are ejected from their upper lip, substrates are oxidised by enzymes and redundant energy becomes light
what is a mydocopia’s third limb used for?
cleaning
What is the difference between podocope and mydocope respiratory systems?
Mydocopes can get quite large and have a heart and complex circulatory system, smaller podocopes use diffusion as water is washed over membrane by their legs.
What controls restrict ostracod ecology?
- salinity
- food supply
- oxygen
- substrate
- depth/pressure
- latitude (temperature gradient)
Describe the different carapace morphologies of ostracods
Freshwater: generally smooth, thin and simple bean shaped carapace
Pelagic: also thin but have rostral notch to allow for swimming appendages
Marine benthic: heavily calcified and ornamented (punctae, reticulation, spines, costae)
Describe the different types of benthic ostracod:
Burrower: baked bean and smooth
Epifaunal: flattened ventral surface, alar wings/frills/keels and/or lateral spines
Coarser substrates have heavily calcified ribs and reticulation
What could a dome shaped carapace suggest?
High pressure, living in water column
When were the major ecological transitions?
- Terrestrial in Carboniferous
- Planktonic in Silurian
- Origin in Cambrian
How did they become so prolific?
- read article*
- Developed good physiological and morphological characterists early on in Cambrian
- They beat the Archaeocopids (Bradoriids and phosphatocopids)
- Bradoriids couldn’t cope with widespread anoxia OR elevated Cambrian oxygen levels
- Bradoriids couldn’t shut their shells so couldn’t burrow and were exposed to the water column
- Phosphatocopids were adapted for Cambrian shelf dysoxia and couldn’t close valves so couldn’t deal with L.Cam. O2 increase
- Ostracods could close their valves and tightly too due to overlapping seal, also avoid predation too
- Ostracods nest together and breathe together avoiding hypoxia
Why did ostracods beat Archaeocopids?
- Bradoriids couldn’t cope with widespread anoxia OR elevated Cambrian oxygen levels
- Bradoriids couldn’t shut their shells so couldn’t burrow and were exposed to the water column
- Phosphatocopids were adapted for Cambrian shelf dysoxia and couldn’t close valves so couldn’t deal with L.Cam. O2 increase
- Ostracods could close their valves and tightly too due to overlapping seal, also avoid predation too
- Ostracods nest together and breathe together avoiding hypoxia
Describe ecology of silurian ostracods
- increase in benthic diversity and abundance into deeper water
- pelagic forms developed from benthic (Wenlock)
- possible deep sea or burrowers
- reduced and enhanced salinity faunas develop
How can we work out when the first pelagic forms developed?
- They become more geographically distributed when they become pelagic, from one coast to another
- found with graptolites in deep marine
Why did ostracods wait till the Silurian to become pelagic?
- newly available ecospace? following major graptolite extinction
- sea bed anoxia?
- acting on pre-adaptations (only mydocopes not podocopes)
How did ostracods become terrestrial from marine?
- moved to brackish water in late devonian
- Freshwater in Carboniferous
- already evoloved mechanisms to deal with osmotic pressure change when moving to freshwater in ordovician
- found in cyclothem freshwater and marine beds and red beds
- In Carboniferous there was major sea level fluctuation and diversification of plants and food supply
- When flooding occurs it could leave large bodies of water isolated (passive) or organisms actively swam up esturaries
