retrusive การใช้

• Protrusive spreite result from movement of the organism away from its burrow entrance ( i . e ., a downward movement in vertical burrows ), whereas retrusive spreite result from movement towards the burrow entrance ( i . e ., an upward movement in vertical burrows ).
• Vertical burrows with retrusive spreite are also referred to as " escape burrows ", as they represent attempts by the organism during periods of high sedimentation to prevent the burrow entrance from being buried, and at the same time keep the bottom of the burrow at the same depth from the sediment-water interface.
• These indicate that the trace was produced under predominantly erosive conditions where the organism was constantly burrowing deeper into the substrate as sediment was eroded from the top . " D . yoyo " has both protrusive and retrusive spreiten indicating highly variable conditions ( erosional and depositional ) leading to the need for the organisms to constantly adjust itself up and down within the substrate to maintain equilibrium and not become exposed or buried.