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#torsion

3 public questions tagged with this topic.

Animal Classification

Torsion results in the anus opening

Torsion fundamentally reorganizes gastropod body architecture during larval development. Rotation of visceropallium through 90 to 180 degrees brings originally posterior mantle cavity containing ctenidia, osphradia, anus and nephridiopores to anterior position dorsal to head and anterior to heart. Alimentary canal becomes sharply U-shaped, anus now discharging above mouth near head, creating sanitation problem. Advantage lies in ability to withdraw head-foot into shell with mantle cavity opening anteriorly facing incoming water current, enhancing respiratory flushing and predator protection, b

Ref: Campbell Biology, 12th ed., Chapter 33: Gastropoda torsion consequences; Brusca & Brusca

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Animal Classification

Gastropods show asymmetry due to

Gastropods are fundamentally bilaterally symmetrical larvae but become secondarily asymmetrical through embryonic torsion occurring during veliger stage, involving 180-degree anticlockwise rotation of visceropallium, mantle and shell relative to head-foot axis. Detorsion secondarily reduces it in opisthobranchs and pulmonates. Torsion relocates mantle cavity from posterior to anterior dorsal position above head, induces chiastoneury crossing pleurovisceral connectives into figure eight, causes loss of right ctenidium and kidney. Differential growth and asymmetric retractor muscle contraction d

Ref: Campbell Biology, 12th ed., Chapter 33: Gastropod torsion; NCERT Class 11 Animal Kingdom

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Animal Classification

Which class shows embryological torsion?

Embryological torsion is hallmark of Class Gastropoda occurring during veliger stage, involving 180 degree counterclockwise rotation of visceral mass, mantle and mantle cavity relative to head-foot, bringing mantle cavity and anus anteriorly above head. Facilitates withdrawal into shell for defense, allows head to emerge first when crawling, but imposes sanitation problem where excreta released near head, partially mitigated by asymmetry loss of one ctenidium. Nervous system becomes figure-eight due to visceral loop twisting. Detorsion occurs secondarily in opisthobranchs and nudibranchs. Biva

Ref: Campbell Biology, 12th ed., Chapter 33: Gastropod Torsion; NCERT Class 11, Chapter 4, Gastropoda

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