Comparisons With Other Phylums

There are many simmilarities between the annelids and the mollusks. biologists believe that the two phyla are very closely related, branching off from a common ancestor during the precambrian period, about 600 million years ago. The mollusks are bilateral like the annelids. They also share a one-way digestive system characteristic. molluscs are the only phylum of ceolomate without segment bodies. they both have a hydrostatic skeleton for movement. Trochophores the larval stage of life for a mollusk, also appears in segmented worms, in the phylum annelida. .The octopus and the squid, 2 species of mollusk, have some of the most complex nervous systems, held by invertebrates. the giant squid is the world's largest invertebrate.