Explain the phylum MOLLUSCA
Answers
Mollusca is one of the most diverse groups of animals on the planet, with at least 50,000 living species (and more likely around 200,000). It includes such familiar organisms as snails, octopuses, squid, clams, scallops, oysters, and chitons.
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda.
Molluscs are found in all habitats: oceans, corals,reefs,forests and even underground. Hence, they are terrestrial as well as aquatic.
These are bilaterally symmetrical animals. But in some molluscs like pila, the adults become asymmetrical.
They have organ system level of organization.
They are triploblastic animals.
They have unsegmented body.
They possess a true body cavity lined by mesoderm. Hence, they are coelomates.
Body is covered by a calcareous shell and is unsegmented with distinct head, visceral hump and muscular foot.
Digestive system is complete and is extracellular.
Respiratory organs are gills present in mantle cavity.
Open circulatory system is present and respiratory pigment is haemocyanin.
They are dioecious and both external and internal fertilisation is found. Usually internal fertilisation is more common.