GENERAL CHARACTERS OF MOLLUSCA

General characters:- 

1. Majority of molluscs are marine,some are freshwater forms and other live on land also.
2. Molluscs have soft and unsegmented body.
3. They are trophoblastic and true coelomate animals.
4.  Important character of molluscs is presence of a shell which is either external or internal. 
5. The shell is made up of calcium carbonate (CaCO2).
6. Body is divisible into head ,ventral foot,mantle and visceral mass.
7.  Alimentary canal is simple and straight tube.some times it is U shaped or shows coiling.
8. Respiratory organs are gills or ctenidia.
9. Circulatory system is open type and blood flows in lacunae.
10. Nervous system is well developed.
11. Sexes are separate through some hermaphrodite individuals are present.
12. Fertilization is internal or external.Development is direct or indirect with trochopore or velliger larvae in the life history.
    
     Example:-Dentalium