Write short note on torsion.
Answers
INTRO
TAXONOMY
DISTRIBUTION AND ECOLOGY
LIFE HISTORY
TORSION
EVOLUTION
REFERENCES
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TORSION
TORSION (Brusca and Brusca, 2002)
Torsion is the rotation of the visceral mass and foot 180 degrees with respect to the head and foot, and is a unique synapomorphy of modern gastropods. Torsion occurs during development in all gastropods, usually in the late veliger stage. However, some gastropods do not remain torted when becoming adults. Torsion is very variable among gastropods and is not a symmetrical process.
When viewed from the top, torsion is counterclockwise. The mantle and anus of the gastropod are moved to the anterior position. The gut is twisted to U-shape, with the nephridia reversing sides. Gonads and gills are not fully developed during torsion, but the nervous system twists into a streptoneury or figure-8 configuration.
Because the anus is now in the anterior position, the gastropods are not able to grow in length. As a consequence, increasing animal length produces loops and coils, with the shell forming a cavity to store the internal organs. After torsion, the left gonad is lost and the right gonad remains, as well as the nephridiophore. The isolation of the reproductive system is thought to explain the expansion of reproductive organs of the neogastropods.
TORSION ADAPTATION
Zoologist Walter Garstang suggested that torsion is an adaptation of the veliger larvae in escaping predators by retracting the head and velum. Other hypotheses suggest that the longitudinal head-foot alignment of gastropods allows greater elongation without toppling sideways.
As a solution to the possible fouling effect of torsion (where mouth and anus are in the same anterior position), scientists suggest that in the earlier stages of torsion, holes and slits are formed in the shell. These holes serve as a control for a one-way water flow where water comes in and passes through the ctenidia, and then out through the holes and slits.
Torsion can be defined as the condition in which the tissues around the testicles are not attached properly.
Explanation:
Testicular torsion can be defined as the condition when the tissues around the testicles are not attached well.
In this condition the testes are twisted. the spermatic chord which in turn abrupts the blood flow towards the testicles.
This causes inflammation in the testes which should be treated as an emergency condition.
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