The registry only covers the shells of nautiluses and "Spirula" and the eggcases of "Argonauta". Cuttlefish, squid, spirula, vampire squid, and cirrate octopuses have small internal shells. "Spirula spirula" is a deep water squid-like cephalopod. Spirula spirula is a species of deep-water squid-like cephalopod mollusk. The "Spirula" shell begins as an organic structure, and is then very rapidly mineralized. "Spirula" is likely the closest living relative of the extinct belemnites and aulacocerids.