Modes of Life


SHALLOW INFAUNAL

  • Shallow infaunal bivalves live just in the sediment on the sea or river floor.
  • They tend to have a height:length ratio of 1.
  • To make burrowing into the sediment easier, these bivalves tend to be smooth and streamlined.
  • Spines may be present so that predators are unable to remove them from the sediment.

DEEP INFAUNAL

  • Deep infaunal bivalves live deep within the sediment on the sea or river floor.
  • They are at least twice as long as they are high.
  • They first appear in the fossil record roughly 2 million years ago. This style of life took much longer to develop because fused siphons had to evolve, as deep sediment living is a difficult mode of life.
  • Opening the valves and pushing the muscle foot downwards achieves burial.

EPIFAUNAL

All bivalves have the ability to secrete sticky threads known as byssal threads. However, most bivalves tend to use them only during infancy when they are small and require stabilization.


Species such as Mytilus use their byssal threads into adulthood. Mytilus is an epibyssate bivalve, which means it lives on the sediment surface with its threads reaching down into the substrate for stability. Epibyssate forms tend to be squat in shape.

Bivalves can also be endobyssate whereby they are situated half in and half out of the sediment with their byssal threads securing them to the sediment. This type of bivalve characteristically displays a pointed anterior.

Byssally attached bivalves tend to be found in high-energy environments.

OTHER INTERESTING MODES OF LIFE

CONSTRAINTS ON A BIVALVE'S MODES OF LIFE
There are several environmental factors that can determine a bivalve's mode of life:


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