2026-04-23 東京大学
図１・カイダコの石灰質の貝殻（卵鞘）
＜関連情報＞
- https://www.um.u-tokyo.ac.jp/research/umutnews/umutnews20260423.html
- https://www.nature.com/articles/s41598-026-45670-3
アルゴノートタコの殻状卵嚢における球晶状繊維状プリズム構造の機能形態と形成論理に関する微細構造学的知見 Microstructural insights into the functional morphology and formation logic of spherulitic–fibrous prismatic architecture in the shell–like eggcase of the argonaut octopods
Kazuki Hirota,Takenori Sasaki,Taro Yoshimura,Shunsuke Onodera,Hirosuke Hirano,Takeshi Toyama,Masa-aki Yoshida & Davin H. E. Setiamarga
Scientific Reports Published:22 April 2026
DOI:https://doi.org/10.1038/s41598-026-45670-3
Abstract
Argonautid octopods (genus Argonauta) possess a unique shell-like biomineralized eggcase, which was suggested to be produced by the first dorsal arms rather than by the mantle tissue, as in typical molluscan shells. In this study, we conducted scanning electron microscopy to investigate the microstructures of both undamaged and post-repair eggcases. Our analysis revealed that a normal eggcase comprises five layers: an outermost organic membrane, an outer spherulitic-fibrous prismatic layer, a middle organic layer, an inner spherulitic-fibrous prismatic layer, and an innermost organic membrane. Both prismatic layers exhibit bidirectional growth from the middle organic layer, a unique feature not observed in typical molluscan shells but, intriguingly, resembles the microstructures of cuttlefish cuttlebones, stony coral calcareous skeletons, and avian eggshells, indicating possible convergence. We propose that the observed eggcase microstructure is formed in four stages: nucleation on the organic scaffold, bidirectional crystal growth from the organic mid-layer, crystal growth perpendicular to the eggcase surface, and organic membrane encapsulation. We also identified two possible repair mechanisms: reattachment of broken fragments and regeneration via new secretions. Our findings thus question the assumed role of the first dorsal arms in calcification. The eggcase also represents the formation of a complex extended phenotype through convergence.
