TORSION AND DETORSION IN GASTROPODS PDF DOWNLOAD

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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There are two different developmental stages which cause torsion. The coil of visceral sac torsion and detorsion in gastropods was primarily dorsal or exogastric becomes ventral or endogastric after torsion. At the head end, water flow is propelled and directed by cilia that bring in nutrients past the gill.

The torsion or twisting of the visceral mass of larval gastropods is not the same thing as the spiral coiling of the shellwhich is also present in many shelled torsion and detorsion in gastropods.

The coil of the visceral sac and the shell, which primitively was dorsal or exogastric, becomes ventral or endogastric, after torsion.

Give an account of torsion and detorsion in gastropoda

With this spiral coiling one may confuse another process called torsion of the visceral mass, gastropode this coiling evolved before torsion. Torsion is very variable among gastropods and is not a symmetrical process. A ring of tentacles lies at the anterior end of the body and the torson hump is posterior, the original mantle cavity has become torsion and detorsion in gastropods. Predaceous foes, still drifting by in numbers unabated, Were baffled now by tactics which their dining plans frustrated.

Torsion takes place quickly and is completed from minutes.

In Cephalopoda the body has become torsion and detorsion in gastropods elongated along the dorso-ventral axis, and as a result of change in the method of locomotion this axis has become the functional anteroposterior axis. This is due to the back and forth motion of the shell during movement, which would tend to block the mantle opening against the foot if it was torsino a posterior position.

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give an account of torsion and detorsion in gastropoda –

Unfortunately it is a bit expensive but all good libraries should be urged to get a copy. After torsion the position becomes endogastric in which visceral mass points backwards and intestine lies in the whorls of the shell and anus opens on the anterior side.

Various degree of detorsion are met within the Euthyneura. 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. The right connective with its torsion and detorsion in gastropods ganglion passes over the intestine called the supraintestinal and the left connective passes below the intestine called torsiion infraintestinal. In this way, a secondary external symmetry is re-established.

Answer Now and help others. In Hydatina physis, there is a thin shell, large torsion and detorsion in gastropods coloured animal, no operculum, and the mantle opening has moved down the right side of the body. Torsion allows foot to be retracted edtorsion the head for better protection of head.

Once the shell has gone, the gills have no choice – they are nude! The gills are directed laterally but lie posterior to the heart and the body becomes symmetrical. Torsion changes the orientation of the mantle cavity and its organs, and the organs of the left side tend to be reduced or even lost. Comment on Gastropod torsion torsion and detorsion in gastropods Manjit Hansra.

This page was last modified on 8 Juneat Before torsion, the anus, the ctenidia and the renal orifices point backwards, and the auricles lie behind the ventricle. On the origin and evolution of major gastropod groups, with special reference to the Streptoneura Mollusca.

As a solution to the possible detlrsion effect of torsion where mouth and anus are in the same anterior positionscientists suggest that in the earlier stages of torsion, holes and slits are formed in the shell. Torsion begins in stages 2 and 3, with a partial rotation of the gut. Some gills in nudibranchs are clearly torsion and detorsion in gastropods the original gills but are secondary structures. It is not clear whether torsion is an advantage or not to the animal, or if it gastroposs any evolutionary significance, but it takes place during the embryological development of gastropods, the larva is a first bilaterally symmetrical, then quite suddenly it undergoes torsion.

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Primitive Gastropods were not twisted and the gills were attached posteriorly inside the mantle jn. In aeolids and tritoniids the original gill is lost and torsion and detorsion in gastropods papillae or cerata have evolved to take their place.

Torsion (gastropod) – Wikipedia

Gills and kidney move from left to right side and in front which helps in breathing. Here’s how it works: During torsion the visceral mass remains almost unchanged anatomically. 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.

Totsion lacking in-text citations from November All detorxion lacking in-text citations.

The visceral hump together with the protecting shell becomes coiled to economies the volume. Gills of the dorid nudibranch Platydoris showing the anal papillae arrow intimately connected. The mantle cavity was primitively posterior in position.

Torsion has played the most important role in the evolutionary history of Gastropoda. Detorsion takes place in Pulmonata, such as Acteon and Bulla in which anus and ctenidium are directed laterally. To maintain the balance of body the shell of the gastropods prolonged anteriorly. This page has been accessed 16, times.

Mantle cavity also must open on the anterior side for easy respiration.