how many species of mollusks are found in the world
Â© Jonathan Bird/ORG. For educational use only. There are over 50,000 known species of Mollusks, which makes them second only to the Arthropods in invertebrate phylum size. Among the Mollusks are some of the most well known of invertebrate sea creatures, like snails, clams, mussels, squid, and octopods.Although one might not see an obvious physical relationship between a snail and a squid, they are remarkably similar in construction.n general, mollusks have 3 body regions: a head, a visceral mass, and a foot.. The head contains the sense organs and brain, while the visceral mass contains the internal organs. The foot is the muscular lower part of the body which is in contact with the substrate.