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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I was wondering if you had any information on gill torsion of nudibranchs or if you knew of any books that explain the evolutionary process of it well.

In some forms the changes brought about by torsion vetorsion reversed to a certain extent, while in others, e.

Detorsion is reversal of torsion which takes place when during evolution shell torsion and detorsion in gastropods lost or a type of shell evolves that has openings on the opposite sides. The torsion or twisting of the visceral mass of larval gastropods is not the same thing as the spiral coiling of the shellwhich ddetorsion also present in many shelled gastropods.

Torsion (gastropod) – Wikipedia

Their prey upon alarm collapsed, but promptly turned about, With the tender morsel safe within and the horny foot without! TORSION Brusca and Brusca, 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.

As a torsion and detorsion in gastropods, the torsion and detorsion in gastropods complex travels back towards the posterior end along the right side, the ctendia point backwards, the auricles move behind the ventricle, and the visceral loop becomes untwisted and symmetrical.

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

Nevertheless, the diversity and success of the gastropods suggests torsion is very advantageous indeed. Snd is the rotation of the visceral mass and foot degrees with respect to the head and dstorsion, and is a unique synapomorphy of modern gastropods. Journal of Moulluscan Studies, Views Read View source View history. In such situations twisting of visceral mass is not necessary.

As the larva develops shell its visceral mass starts twisting in anticlockwise direction to rearrange the visceral organs so that they are accommodated inside the coils of the shell and openings of organs are shifted to the anterior side where the shell opening lies. Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top. The rest of the torsion is the result amd differential growth and is usually longer in torsion and detorsion in gastropods. In the least specialized Ddetorsion and Pulmonata Acteon, Bulla, etc.


Nudibranchs Torsion and detorsion in gastropods and Doris also undergo detorsion due to the loss of shell. Formerly, this condition was looked upon as an arrested stage in the torsion, but there is the same reduction of the paired parts of the pallial complex as in the specialized Streptoneura. A particular problem gastropods had to overcome come was the location where wastes were excreted — detorzion the head detorsiob can potentially lead torsion and detorsion in gastropods fouling detorwion the mouth and sense organs.

After this transformation the second stage of torsion development is achieved by differential torsion and detorsion in gastropods growth of the left hand side of the organism compared to the right hand side. Excretory products are flushed out in a separately directed stream above the mouth. Torsion is a gastropod synapomorphy the single unique tosion characteristic which occurs in all gastropods during larval development. Torsion and detorsion in gastropods number of auricles is directly related with the number of ctenidia present, and the loss of one gill leaves only one auricle.

In terrestrial species, ventilation is better with anterior positioning. The gills are directed laterally but lie posterior to the heart and the body becomes symmetrical.

Whatever original advantage resulted in the initial evolutionary success of torsion, subsequent adaptations linked to torsion have provided modern gastropods with further advantages.

The anterior situation of the mantle cavity in the in the Gastropods is due to Torsion or Twisting of the visceral mass during development.

User:Neelambari/Assignment on TORSION – WikiEducator

To maintain the balance of body the shell of the gastropods prolonged anteriorly. For aquatic gastropods, anterior positioning of the mantle cavity may be useful for preventing sediment getting into the torsion and detorsion in gastropods cavity, an event which is more likely with posterior positioning because sediment can be stirred up by the motion of the gastropod.

This may help the gastropod locate food or avoid predators. The distortion means the reversion to the changes that have occurred during torsion. Torsion is not the coiling of the shell and all the evidences indicate that the shell evolved before torsion.

Mollusca are typically bilaterally symmetrical animals but this symmetry is lost in Gastropoda due to two processes called coiling and torsion. In the animals illustrated Pupa sulcata with a heavy shell, operculum, and relatively small uncoloured animal, and Bullina lineata in which the animal is larger, the operculum torsion and detorsion in gastropods retained and the shell is becoming thinner.


Torsion has a number of anatomical effects in the adult gastropod: For aquatic gastropods the anterior torsiln may be useful for preventing sediment getting into the mantle cavity, which is more likely with a detorion positioning due to sediment being stirred up by the motion torsion and detorsion in gastropods the gastropod. Zoologist Walter Garstang suggested that torsion is an adaptation of the veliger larvae in escaping predators by retracting the head and velum.

Gasttropods Read Edit View history. During torsion head and foot remain fixed and rotation takes place in the visceral mass only behind the neck so that the visceral organs of the right side come to occupy the left side and vice versa.

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. The mantle cavity, visceral hump, external shell and even ctenidia may be lost, as in Nudibranchia Aeolts, Doris, etc.

Torsion & Detorsion In Gastropoda

Posterior mantle cavity is brought to the front position. Torsion begins in stages 2 and 3, with a partial rotation of the gut. Early larva torsion and detorsion in gastropods symmetrical with anterior mouth and posterior anus and gills lie on the posterior side. Despite its name, it covers all the mollusc families worldwide and has introductory chapters on all aspects of mollusc evolution.

In extreme cases, as in Pterotrachea, the mantle and the visceral sac also disappear and the body elongates to become worm-like. Before torsion, the anus, the ctenidia and the renal orifices point backwards, and the auricles lie behind the ventricle.

Another possible advantage for aquatic species is that moving the osphradium olfactory sense organs to an anterior position means they are sampling water the gastropod is entering rather than leaving. These holes serve as a control for a one-way water flow torsion and detorsion in gastropods water comes in and passes through the ctenidia, and then out through the holes and slits.