Ostracoda

Question 1

Name Ostracod key characteristics

Answer 1

• 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

Question 2

Name the 3 main anatomical features of an ostracod carapace:

Answer 2

• bivalved calcite carapace
• have to moult the carapace as they grow
• carapace is hinged dorsally

Question 3

Is there evidence of ostracoda in the Cambrian?

Answer 3

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

Question 4

What are Leperditicopids?

Answer 4

They look like ostracods and favoured shallow marine lagoons but are too big! (can’t find any soft parts either)

Question 5

Name the different types of hinge:

Answer 5

• Adont (flat/smooth)
• Merodont (some overlap possibly some roughness)
• Amphidont (very rough strong overlap)

Question 6

Podocope limbs are…

Answer 6

biramous (with inner and outer branches)

Question 7

How are mydocopia adapted to pelagic life?

Answer 7

• They have strong muscles and powerful second antennae that extend from the rostral notch
• calcite shell is smooth, thin and light

Question 8

Describe mydocopia courtship behaviour:

Answer 8

Males of some species attract females using bio-luminescence, each species has its own pattern

Question 9

How do mydocopia produce bio-luminescent chemicals

Answer 9

Chemicals are ejected from their upper lip, substrates are oxidised by enzymes and redundant energy becomes light

Question 10

what is a mydocopia’s third limb used for?

Answer 10

cleaning

Question 11

What is the difference between podocope and mydocope respiratory systems?

Answer 11

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.

Question 12

What controls restrict ostracod ecology?

Answer 12

• salinity
• food supply
• oxygen
• substrate
• depth/pressure
• latitude (temperature gradient)

Question 13

Describe the different carapace morphologies of ostracods

Answer 13

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)

Question 14

Describe the different types of benthic ostracod:

Answer 14

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

Question 15

What could a dome shaped carapace suggest?

Answer 15

High pressure, living in water column

Question 16

When were the major ecological transitions?

Answer 16

• Terrestrial in Carboniferous
• Planktonic in Silurian
• Origin in Cambrian

Question 17

How did they become so prolific?

Answer 17

• 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

Question 18

Why did ostracods beat Archaeocopids?

Answer 18

• 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

Question 19

Describe ecology of silurian ostracods

Answer 19

• 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

Question 20

How can we work out when the first pelagic forms developed?

Answer 20

• They become more geographically distributed when they become pelagic, from one coast to another
• found with graptolites in deep marine

Question 21

Why did ostracods wait till the Silurian to become pelagic?

Answer 21

• newly available ecospace? following major graptolite extinction
• sea bed anoxia?
• acting on pre-adaptations (only mydocopes not podocopes)

Question 22

How did ostracods become terrestrial from marine?

Answer 22

• 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