Phylum Mollusca (Snails, Squids, Octopuses, Chitons, Scallops, & Clams)

Largest: By length the Giant Squid (Architeuthis dux) is the largest mollusc at approximately 40 feet (12.2 meters) long

giant squid Derek Keates Flikr — Giant squid : Photo by Derek Keates via Flikr

Smallest: The small marine snail, Ammonicera minortalis, at only 0.015 inches (0.4 millimeters) in diameter

ammonicera Flikr Salyangoz — Ammonicera : Photo by Salyangoz via Flikr

References

Roper CFE & Boss KJ (1982) The giant squid. Scientific American 264(4):96-105.

Bieler R & Mikkelsen PM (1998) Ammonicera in Florida: notes on the smallest living gastropod in the United States and comments on other species of Omalogyridae (Heterobranchia). Nautilus 111:1-12.