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Difference between molluscs and arthropods :

TThe key difference between mollusks and arthropods is that mollusks are soft bodied invertevrates with one or two shells while arthropods are animals with segmented bodies, paired appendages and an exoskeleton.

Difference between annelids and vertebrates:

TThe difference between annelids and vertebrates is that haemoglobin is present in the plasma of annelids and in vertebrates haemoglobin is present in RBC.

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The difference between mollusks and arthropods is that mollusks are soft-bodied invertebrates with one or two shells while arthropods are animals with segmented bodies, paired appendages and an exoskeleton.
Haemoglobin is present in the plasma in Annelids. In vertebrates haemoglobin is present in RBC