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Few studies have simultaneously examined shell size and changes in the surface and interior of the exoskeleton across a wide range of body weights in mud crabs. This study first analyzed the relationship between the sex, weight, and shell size of 131 mud crabs caught in Okinawa, and compared the findings with data from seven regions. Next, using laser microscopy and nanoindentation, the study examined how surface morphology, internal structure, exoskeleton thickness, hardness, and Young's modulus change with body weight (BW) in 18 male crabs, weighing 249 g to 1920 g. The growth coefficients of mud crabs in Okinawa were 3.52 for males and 2.91 for females, and these values were the largest among those reported so far in various countries. The exoskeleton surface in mud crabs consisted of a bimodal bulge structure with a large bulge 264.5 μm in diameter and a small bulge 100 μm in diameter. Such surface morphology and thickness of the hard exocuticle of 150 μm were independent of BW. On the other hand, the endocuticle thickness increased with BW. Even if the exoskeleton feels hard, the endocuticle may be thin because it is not fully developed by the effect of molting.

Rights:

• Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International
  

Keyword: Crustacean cuticle, Bimodal bulge structure, Biomineralization, Structure-property relations, Protection

Date published: 2025-09-05

Publisher: Elsevier BV

Journal:

• MATERIALS & DESIGN (ISSN: 02641275) vol. 258 114699

Funding:

• Japan Society for the Promotion of Science JP21H04537

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1016/j.matdes.2025.114699

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Updated at: 2025-09-09 16:30:28 +0900

Published on MDR: 2025-09-09 16:18:44 +0900