Question

why are arthropods called largest phylum as mollusca are bigger than arthropod

Answer 1

Arthropod, any member of the phylum Arthropoda, the largest phylum in the animal kingdom, which includes such familiar forms as lobsters, crabs, spiders, mites, insects, centipedes, and millipedes. ... Arthropods lack locomotory cilia, even in the larval stages, probably because of the presence of the exoskeleton.