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Question
In the phylum Mollusca although there is bilateral symmetry, but it is lost in some forms, due to the phenomenon, called as
In the phylum Mollusca although there is bilateral symmetry, but it is lost in some forms, due to the phenomenon, called as
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Solution
The correct option is D Torsion
The organisms like the snails, slugs, sea butterflies and sea hares belong to the group of Gastropoda. This is a class which contains various species of molluscs. They are found in sea. They are also found in the fresh water and land. They are bilaterally symmetrical. Due to the torsion. the body of certain organisms have become asymmetrical. Torsion occurs at the larval stage. This torsion involves the visceral hump. The two foot retractor muscles develop at different rates. Along with the uneven secretion rate of the shell from the mantle, twists the visceral mass through 90−180090−1800. This brings the mantle cavity and anus to the side or over the head region.
Thus, the correct answer is option B.
The organisms like the snails, slugs, sea butterflies and sea hares belong to the group of Gastropoda. This is a class which contains various species of molluscs. They are found in sea. They are also found in the fresh water and land. They are bilaterally symmetrical. Due to the torsion. the body of certain organisms have become asymmetrical. Torsion occurs at the larval stage. This torsion involves the visceral hump. The two foot retractor muscles develop at different rates. Along with the uneven secretion rate of the shell from the mantle, twists the visceral mass through 90−180090−1800. This brings the mantle cavity and anus to the side or over the head region.
Thus, the correct answer is option B.
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