Torsion and detorsion in gastropoda is described with examples. Torsion is the rotation of the visceral mass and foot degrees with respect to the head and foot, and is a unique synapomorphy of modern gastropods. Torsion . And to understand what that means we need to know what “torsion” is. In simple terms, the primitive gastropod snail has twisted its body so that the posterior end .

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Ad Acteon and Bulla detorsion is partial, and complete detorsion torsion and detorsion in gastropods observed in Aplysia. The visceral hump grows faster on one side than on the other, so that it is twisted into a compact spiral which is directed posteriorly to keep the balance of the animal, the shell is also coiled.

Before torsion the gastropod has an euthyneural nervous systemwhere the two visceral nerves run parallel down the body. Visceral mass has to undergo rearrangement so that openings of kidneys, gonads and anus should migrate to torsiion front side which is the only opening torsion and detorsion in gastropods the shell.

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As a result of detorsion the pallial complex travels towards the posterior end along the right side. One likely candidate for the original purpose of torsion is defence against predators in adult gastropods. After torsion, the anus, the ctenidia and the renal orifices project forward, and the auricles lie in front of the ventricle.

It is further complicated by potential problems that accompany torsion. Torsion can provide other detrsion. An Example of Phylum Annelida: Associated with this is the process of “Detorsion” where the mantle cavity and its associated organs move from above the head down the right side torssion the body towards the posterior end.

In this way, a secondary external symmetry is re-established. Torsion and detorsion in gastropods a few examples. The torsion or twisting of the visceral mass of larval gastropods is not the same torsion and detorsion in gastropods as the spiral coiling of the shellwhich is also present in many shelled gastropods.


Torsion and detorsion in gastropods below mentioned article provides a brief account of torsion and detorsion in Gastropoda. A particular problem gastropods had to overcome come was the location where wastes were excreted — above the head which can potentially lead to fouling of the mouth and sense organs.

When treated as a homologous feature throughout Gastropoda, torsion tends to take on a structural definition synonymous torsion and detorsion in gastropods the torted anatomical condition. Authorship details Rudman, W. It is not clear whether torsion is an advantage or not to the animal, or if it has any evolutionary significance, but it takes place during the embryological development of gastropods, the larva is a first torwion symmetrical, then quite suddenly it undergoes torsion.

Articles lacking in-text citations from November All articles lacking in-text citations. Retrieved from ” http: As a result, the parietal ganglions end up at different heights.

Torsion (gastropod)

Some gastropods can also close the entrance to their shell with a tough operculuma door-like structure which is attached to the dorsal surface of their foot. Detorsion is brought about by reversal of the above phases. Best wishes, Bill Rudman.

The evolution of an asymmetrical conispiral shell allowed gastropods to grow eetorsion, but resulted in an unbalanced shell. An Example of Phylum Mollusca: Detorsion takes place in Pulmonata, such as Acteon and Bulla in which anus and ctenidium are directed laterally. Dwtorsion may help the aand locate food or avoid predators. Transition is shown from torsion and detorsion in gastropods straight line body plan of the primitive detorwion to a fully torted body plan found in Caenogastropod snails; for example, the cone shell mollusc.

Predaceous foes, still drifting by in numbers unabated, Were baffled now by tactics which their dining plans frustrated.

The Gastropods on the other hand, possess an asymmetrical body with the mantle cavity lying anteriorly and the shell and the visceral mass coiled spirally and directed posteriorly. This page was last edited on 19 Marchat The gut is twisted to U-shape, with the nephridia reversing sides. Torsion has played the most important role in the evolutionary history of Gastropoda. If you have no luck let me know and I’ll look out a couple of useful references.


Ninety percent of the torsion is affected by the right retractor muscle which is quite prominent in the larva while detkrsion left retractor muscle is rudimentary.

At the head end, water flow is propelled and directed by cilia that bring in nutrients past the gill. The mantle dettorsion, enclosed by the shell sits above the head, and faces forwards, as do the anus and all the other openings situated in the mantle cavity.

There are many torsion and detorsion in gastropods advantages torsion provided gastropods. Look up torsion in Torsion and detorsion in gastropods, the free dictionary. Torsion is very variable among gastropods and is torsion and detorsion in gastropods a symmetrical process.

Some examples of this are: Ctenidium travels backwards or to the lateral torsion and detorsion in gastropods. The small chemoreceptor osphradium also migrates to the front side so that it could chemically analyse water current entering the mantle cavity. In the schematic diagram above, rotation of the straight line body, and a subsequent twisting known as torsion, is illustrated as a progressive transition.

The Sea Slug Forum – Torsion and detorsion

The long, uncoiled pleura-visceral nerve connectives become twisted into a figure of 8. In majority of the gastropods torsion, as already stated, is resulted in two stages, viz.

The number of auricles torsion and detorsion in gastropods directly related with the number of ctenidia present, and the loss of dftorsion gill leaves only one auricle. Auricle moves behind the ventricle.