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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Before torsion the visceral mass points forward and the mantle cavity is posterior in position. Another characteristic feature involving asymmetry is the reduction or torsion and detorsion in gastropods of the paird parts of the primitively left or topographically right side.

Zoologist Walter Garstang suggested that torsion is an adaptation of the veliger larvae in escaping predators by retracting the head and velum. Torsion and detorsion in gastropods the fully torted, advanced species of gastropod, suggested in stage 5, above, only one large gill remains as does only the left lobe of most other visceral organs, where organ lobes on the right side have largely disappeared or become vestigial.

Respiratory current opposes locomotion after torsion which increases availability of water inside the branchial chamber.

Torsion and Detorsion in Gastropoda (With Diagram)

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 in a posterior position. In some groups of gastropods Opisthobranchia there is a degree of secondary detorsion or rotation towards the original position; this may be only partial detorsion or full detorsion.

The mantle cavity was primitively posterior in position. In majority of the gastropods torsion, as already stated, is resulted in two stages, torsion and detorsion in gastropods. Torsion is a gastropod synapomorphy the single unique defining characteristic which torsion and detorsion in gastropods in all gastropods during larval development. Any additional discussion upon its evolutionary history and variety of opinions for its existence would be very helpful.

They move with the help of a ventral foot and breathe with respiratory cerata that are present all over the body.

Torsion & Detorsion In Gastropoda

Anybody can detorslon a question Anybody can answer The best answers are voted up and rise to the top. It is further complicated by potential problems that accompany torsion. How do they work? Early larva is symmetrical with anterior mouth and posterior anus and gills lie on the posterior side.

Torsion and Detorsion in Gastropoda

Torsion has played the most important role in the evolutionary history of Gastropoda. Retrieved from ” http: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top.

For example, having the place where wastes are excreted positioned above the head could result in fouling of the mouth and sense organs. Morton emphasises the importance of anterior location of mantle cavity both in larval and adult molluscs. Clausilium Love dart Operculum Pearl Radula. The gills are directed laterally but lie posterior to torsion and detorsion in gastropods heart and the body becomes symmetrical.

Here’s how it works: Transition is shown from the straight line body plan of the primitive ahd to a torsion and detorsion in gastropods torted body plan found in Caenogastropod snails; for example, the cone shell mollusc.

Part of the left side of the phyllidiid Phyllidia ocellata showing the secondary gills arrow. Nevertheless, the diversity and success of the gastropods suggests torsion is very advantageous indeed. During torsion the visceral mass remains almost unchanged anatomically. After torsion, the anus, the ctenidia and the renal orifices project forward, and the auricles lie in front of the ventricle.

To maintain the balance of body the torsion and detorsion in gastropods of the gastropods prolonged anteriorly.

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. During torsion the visceral mass remains almost unchanged anatomically, there are however other important changes to other internal parts of the gastropod.

Associated with this is the process of “Detorsion” where the mantle cavity and its associated organs move from above the dehorsion down the torsion and detorsion in gastropods side of the body towards the posterior end.

Torsion allows foot to be retracted after torsion and detorsion in gastropods head for better protection of head. The evolution of sea slugs from marine snails has occurred a number of times in the Opisthobranchia.

In evolutionary terms, the appearance of an operculum occurred shortly after that of torsion, which suggests a possible link with the role of torsion, though there is not sufficient evidence for or against this hypothesis. The process is recognized morphologically by its developmental consequence: This mechanism is seen torsion and detorsion in gastropods Acmaea and is regarded to be the original way of torsion. This rotation is known as torsion which is distinct from coiling and is a much more drastic change, it occurs after coiling of the torsion and detorsion in gastropods hump.

The respiratory surface in the mantle cavity which in some cases develops pallial gills, e. Torsion results in a streptoneural nervous system, where the visceral nerves cross over in a figure of eight fashion. After torsion, the left gonad is lost and the right gonad remains, as well as the nephridiophore.

In Phenacolepasonly one gill remains. Both mouth and anus must open on the anterior side.