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Paper Nautilus or Argonauts are open-water octopi with a unique feature. The females biomineralize an egg case that doubles as a shell they swim with throughout their life. Lacking an outer covering, Argonauta shells are more susceptible to changes in pH in the ocean. These egg cases grow with a delicate ridged ornamentation that radiates out from the center. The pattern and ornamentation of these ridges is known to vary between different species and individuals, but the implications of these different patterns are not well understood.
This project utilizes 3D scanning technology to create digital models of Argonauta shells. We analyzed six shell models across four different species: Argonauta nodosa, A. hians, A. argo and A. nouryi. Using a log spiral fit analysis, we measured multiple aspects of ornamentation to provide insight into variances of shell structure and formation between species. These aspects included rib amplitude, case area, and arc length.
We also used computational fluid dynamics to analyze differences in fluid flow around our shell models. We compared differences in drag and flow paths around the egg case at both the intraspecies and interspecies levels. These differences may highlight a tradeoff between shell surface and vulnerability to pH effects versus hydrodynamic advantage. Understanding differences of hydrodynamic advantages between Argonauta shells can help us understand how different species may be affected by changing pH in the oceans, if species are unable to reach their hydrodynamic advantages as a result of ocean changes.