Shell size of the paper nautilus Argonauta argo (Cephalopoda; Octopoda) stranded on a beach at the southernmost part of the Japan Sea in early winter

The mass stranding of the paper nautilus Argonauta argo occurred on Ohama beach facing the southemmost part of the Japan Sea in early December 1991. The shell length and shell-opening width were measured for 129 specimens. The range of the shell length was 75-185mm. The shell length of 127 specimens remained less than 148mm and showed a single peak of the frequency distribution between 100-110mm. Only two specimens were more than 180mm in shell length. Incubating females occupied 65% of the stranded population. A linear significant relationship was obtained between the shell-opening width and shell length. There was no significant difference in mean shell length between the incubating and non-incubating females.