By GAMNI MADAAN, Academic Content Writer at EDUMARZ
Members of Phylum Mollusca comprise the Second largest animal Phylum. They can be either terrestrial or aquatic .They are coelomate, bilaterally symmetrical, triploblastic and have organ -system of organisation. Their body is unsegmented and mainly covered by a calcareous shell . They have well developed respiratory and excretory functions .Sensory tentacles is present in anterior head region which help in grasping and feeding things.
fertilisation is internal and indirect.
General features :-
Habitat: Mostly aquatic
External Morphology: Unsegmented body with distinct head, muscular foot and visceral hump . Because of soft and spongy skin , a mantle is formed over visceral hump.
Locomotory organ : Muscular foot as Locomotory organ that helps in creeping , swimming and in other activities.
Body Wall and Symmetry :Triploblastic and bilaterally symmetrical
Alimentary Canal and Digestion : Well developed alimentary canal and mouth contains radula that helps in food ingestion.
Respiration: Mantle cavity which is space between hump and mantle contains gills to help in respiration.
Excretion and Osmoregulation: Besides from gills, basic excretory organ such as metanephridia are also present.
Development : Development can be either direct or indirect but usually indirect development takes place
Reproduction and Fertilisation: Sexual reproduction and internal fertilisation. They are oviparous animals i.e they produce through eggs that hatch outside mother’s womb.
Examples:—
Octopus(Devil fish),loligo(Squid),Pila( apple snail),Dentalium(Tusk shell),Pinctada(Pearl oyster),Aplysia(Sea-hare) and chaetopleura(chiton).