This aquatic gastropod mollusk is in the family Tateidae. Spirula spirula is a species of deep-water squid-like cephalopod mollusk. Invertebrates include 97 crayfish species and 383 mollusk species. A shell midden or shell mound is an archaeological feature consisting mainly of mollusk shells. It may be the operculum of a snail-like mollusk found in the Red Sea. The word "seashell" is often used to mean only the shell of a marine mollusk. Fulton named his submarine after a marine mollusk, the chambered nautilus. They are named because of the similarity to the limpet, a mollusk. Radiocarbon dating of freshwater mollusk remains indicated an age of about 7,000 years. Originally the Calabrian was a European faunal stage primarily based on mollusk fossils. One division of malacology, conchology, is devoted to the study of mollusk shells. One of the more studied organisms is a mollusk. There are also high levels of mollusk endemism. This was shown by Gene Block in isolated mollusk basal retinal neurons (BRNs). The divers are attacked by a giant mollusk, which kills one of the divers.