Argonauta Physical description Eggcase
 Female argonauts make a laterally compressed, calcareous eggcase in which they reside. The eggcase curiously resembles the shells of extinct ammonites. After she deposits her eggs in the floating eggcase, the female herself takes shelter in it, often along with the male's detached hectocotylus. She is usually found with her head and tentacles protruding from the opening, but she retreats deeper inside if disturbed. These ornate, curved white eggcases are occasionally found floating on the sea surface, sometimes with the female argonaut still clinging to it. It is made of calcite, with a 3-layered structure Most other octopuses lay eggs in caves, the argonauts may have evolved to use ammonite shells for their egg laying, eventually becoming able to mend the shells and perhaps even make their own.