bivalves 2.

• Epifaunal byssally attached. Byssus - thread like stricture that attaches bivalve to the substate. For example muscles that move in high tides to feed. 

   

  Strong shell - prevents damage due to collisions in high energy.

  Streamlined boring shell - no sharp edges to damage itself on or others in colony and protects in currents. 

  Large adductor muscles - holds valves together tightly to stop shell drying out at low tide. 
• Epifaunal cemented, for example a type of oyster called Ostrea, which secretes a layer of cement from the mantle and becomes attached from the left valve, with one large adductor muscle. 

   

  Strong, thick shell - withstands high energy currents. 

  Strong adductor muscle - keeps heavy shells closed in high energy conditions and opens them for feeding. 

  Different sized valves - smaller valve acts as a lid to the large valve which is cemented. Shell irregularities match substrate. 
• Epifaunal free lying, for example gryphaea a type of extinct oyster. They rested in their convex left valve which is much larger than the right to prevent it sinking into the mud. 

   

  Small right valve - low centre of gravity. 

  Strong thick shell - withstand high energy, curved shape allows feeding apparatus to be above sediment. Growth lines to thicken the shel
• Shallow burrowers: 

  • Ribs/growth lines - grips sediment when burrowing 
  • Small pallial sinus - short siphons 
  • Large muscle scars - helps to close valves 
  • Complete closure of the valves - protection from predators, prevention from drying out. 

   

   
• Deep burrowers:

  • Large pallial sinus - long siphons 
  • Streamlines shell - easier burrowing 
  • Small muscle scars - no need to close valves 
  • Grape on shell - unable to retreat siphons 
• Nektonic:

  • Ribbed/corrugated thin shells - strong but lightweight for swimming
  • One large muscle scar - constant need to open and close shells to swim 
  • Ears on shell - direct currents, straight hinge line improves stability 
  • Lots of tiny eyes on mantle - see movements/shadows, detect predators