Concept explainers
To determine: The functional problem arising due to torsion in gastropods.
Introduction: The shell is first formed in the veliger larval stage of gastropods. This larval stage has two velar lobes and a developing visible foot. Initially, the position of mouth and anus are anterior and posterior respectively. The relative position of the shell, the digestive tract and anus along with the mantle cavity containing gills changes in a process called torsion.
To determine: The ways evolved by gastropods to over the problem caused by torsion.
Introduction:‘Coiling’ is the spiral winding of shells and visceral mass different from torsion. Coiling may occur at the same time as torsion in the larval stage. Although, the fossils records illustrate an early origin of coiling than torsion in gastropods.
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