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. Contraction of the larval retractor muscles and differential growth are possibly responsible for such [...]
In this article we will discuss about the phylogeny and phylogenetic relationship of phylum Mollusca. Phylogeny of Mollusca: The phylogeny of Mollusca is a controversial issue. It was previously argued that Mollusca originated from annelids, generally assumption based on the evidence of fossilized monoplacophorans. But this theory was largely rejected because the body structure of Neopilina galatheae has revealed a [...]
In this article we will discuss about Pearl:- 1. Meaning of Pearl 2. Chemical Composition of Pearls 3. Shape, Size and Colour 4. Formation 5. Species Used in Pearl Culture 6. Distribution of Pearl Oysters in Indian Waters 7. Pearl Fishery in Japan and Other Countries. Meaning of Pearl: Pearl is a spherical or irregular mass formed by the [...]