In general molluscs or mollusks are invertebrates that has hard external shells on their outer body.The various examples of Mollusca are Pila globosa, Unio, Mytilus, Pinctada, Teredo, Loligo, Octopus etc.
Pila globosa: It is common fresh water.In water they respire with the help of gills and on land with pulmonary sacs or lungs. The body is divided into head, visceral hump and foot. Head has a pair of stalked eyes and two pairs of tentacles.The body is enclosed by protective shell.
Unio or fresh water mussel: It is a common bivalve .The outer surface of the shell is marked by numerous concentric linescalled lines of growth. Head is absent. Foot is the locomotory organ. The respiratory organs are the gills.
Mytilus or sea mussel: It is the common edible mussel. It is a sedentary form and remains attached to rocks and other solid objects with the help of bunch of adhesive threads called Byssus threads.
Pinctada or pearl oyster: They are pearl producing bivalves commonly found in the seas. The valves of the shell are unequal and their free margins are characterized by finger like processes. The foot is reduced.
Terredo: It has an elongated soft body covered by a tough mantle. At the anterior end is pair off reduced shells with which the mollusk bores into the wood, turning it into saw dust. Respiration through gills.
Loligo: it is a marine edible mollusc.The body is narrow elongated showing two regions –the head and the trunk.
Octopus: It is a marine bottom dwelling mollusc.The mouth is surrounded by 8 long arms bearing two rows of suckers. Tentacles are absent.