MOLLUSCA

The name Mollusca (from the Latin mollis meaning soft), was first used by the French zoologist Cuvier in 1798 to describe squids and cuttlefish , animals whose shell is reduced and internal, or entirely absent. It was only later that the true affinities between these species and other molluscs, such as snails and bivalves , were fully recognised.

The molluscs are a very successful group. If success is measured in terms of number of species and variety of habitats to which they have become adapted, then molluscs are one of the three most successful groups in the animal kingdom. Over 160,000 species have been described, of which around 128,000 are living and about 35,000 are recorded as fossil species.

Molluscs are found in nearly all habitats. In the sea they occur from the deepest ocean trenches to the intertidal* zone. They may be found in freshwater as well as on land where they occupy a wide range of habitats. Thus, during their evolution, they have become adapted to living in nearly all available habitats.

The phylum Mollusca is normally divided into 8 classes of very unequal importance; the most important class of living molluscs is the Gastropoda comprising more than 80% of all living mollusc species. Although the Cephalopoda still contains a number of living species, fossil evidence suggests that they were once far more abundant than they are today, and were probably the dominant animals of Ordovician* seas।

sumber; http://www-biol.paisley.ac.uk/Courses/Tatner/biomedia/units/moll1.htm