What is torsion and Detorsion?

What is torsion and Detorsion?

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.

What is a spire on a shell?

The spire consists of all of the whorls except for the body whorl. Each spire whorl represents a rotation of 360°. A spire is part of the shell of a snail, a gastropod mollusc, a gastropod shell, and also the whorls of the shell in ammonites, which are fossil shelled cephalopods.

What gastropod means?

Definition of gastropod : any of a large class (Gastropoda) of mollusks (such as snails and slugs) usually with a univalve shell or none and a distinct head bearing sensory organs.

How would you describe the gastropod shell?

The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage.

What is meant by torsion in molluscs?

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 the apex of a shell?

In anatomy, an apex (adjectival form: apical) is part of the shell of a mollusk. The apex is the pointed tip (the oldest part) of the shell of a gastropod, scaphopod, or cephalopod. The apex is used in end-blown conches.

What is mantle in biology?

mantle, also called pallium, plural pallia, or palliums, in biology, soft covering, formed from the body wall, of brachiopods and mollusks; also, the fleshy outer covering, sometimes strengthened by calcified plates, of barnacles.

What is meant by torsion explain the process?

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 in gastropods and its significance?

What is inside a spire?

A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires are typically built of stonework or brickwork, or else of timber structure with metal cladding, ceramic tiling, shingles, or slates on the exterior.

What are twisty shells called?

A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the ammonites.