What is the process of torsion in gastropods?

Torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle, and shell 180˚ with respect to the head and foot of the gastropod. This rotation brings the mantle cavity and the anus to an anterior position above the head.

What is meant by torsion explain the process in detail PDF?

Definition: Torsion (twisting) is the rotation of visceral organs in anticlockwise direction through an angle of 180° on the rest of the body during larval development. The phenomenon takes place in the free-swimming (veliger) larva of gastropods and converts the symmetrical larva into an asymmetrical adult.

What is torsion process?

Torsion is a process in larval gastropods whereby the visceropallium is rotated anti- clockwise through 180° from its initial position on the head-foot complex.

What is torsion and its effects?

Torsion is an important structural action that increases member shear strength. It occurs when it is twisted causing twisting force acting on the member, known as torque, and the resulting stress is known as shear stress. This stress is added to the existing shear stress due to vertical and lateral applied loads.

What is torsion and Detorsion in gastropods?

Torsion allows foot to be retracted after the head for better protection of head. DETORSION. Detorsion is reversal of torsion which takes place when during evolution shell is lost or a type of shell evolves that has openings on the opposite sides. In such situations twisting of visceral mass is not necessary.

How does torsion affect the nervous system of gastropods?

Before torsion the gastropod has an euthyneural nervous system, where the two visceral nerves run parallel down the body. Torsion results in a streptoneural nervous system, where the visceral nerves cross over in a figure of eight fashion. As a result the parietal ganglions end up at different heights.

What is torsion and Detorsion gastropods?

What two ways do gastropods move?

When the foot is narrow, as in Strombus and Aporrhais, the animal moves in fits and starts, tumbling along by a digging action of the foot and the pointed operculum. Certain small gastropod species move by the beating action of cilia of the foot on the mucous sheet secreted by the anterior part of the foot.

Where is torsion used?

A torsion spring is commonly used in clothes pins, clipboards, swing-down tailgates and garage doors. Other application types include hinges, counterbalances and lever returns. Sizes range from miniature, used in electronic devices, to large torsion springs used in chair control units.

What are the applications of torsion?

Different Applications That Use Torsion Springs

• Doors and Hinges. Torsion springs are a vital component in all different types of doors, such as residential doors, garage doors and overhead doors used at loading docks and warehouses.
• Retractable Seating.
• Clipboards.
• Medical Equipment.
• Ceiling Light Fittings.

What is torsion in molluscs?

TORSION AND DETORSION IN MOLLUSCA. TORSION. Torsion is a process in which the viscero-pallium rotates anti-clockwise through 180° from its initial position during larval development. So that the mantle cavity, with its pallial complex, is brought to the front of the body in the adult.

Does torsion have an evolutionary significance on gastropods?

Chiastoneury and Zygoneury Signification of Torsion: As torsion impart an evolutionary significance on gastropods as it appears in ontogeny of the living gastropods.

What is torsion in grastropods?

Torsion may be defined as a pleisiomorphic character trait of evolutionary process present in larval grastropods of phylum mollusca, where the visceropallium of the body is rotated anti clockwise through 180◦ from its original position on head-foot complex arising the asymmetry in visceral organs formation and position.

What are the stages of torsion in heliotes?

(iii) In Heliotes (a gastropod) torsion takes place in two stages as there is only 900 rotation in the first stage and 1800 rotation in the second phase. The animal remains free swimming at first stage when the head lies at right angle to the mantle so head with prototroch could not be withdrawn. Remark : Garstang’s view is not accepted now-a-days.

What are the effects of larval mutation on torsion in snails?

Morton (1958) believes the final effects of torsion due to larval mutation are profound in the adult snails though in a different way: a. Torsion promotes stability in the adult by bringing the body of the snail nearer to substratum. b.