Columnar Structure of Claw Denticles in the Coconut Crab, Birgus latro

Inoue, Tatsuo; Oka, Shin-ichiro; Nakazato, Koji; Hara, Toru

doi:10.3390/min12020274

Cited by 6 publications

(11 citation statements)

References 31 publications

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“…Such a fracture surface effectively improves the fracture characteristics and provides mechanical resistance to avoid catastrophic failure [4,5,[33][34][35][36]. The terrace-step fracture surface was often observed in the exocuticle with a twisted plywood-pattern structure on the fracture surface of the coconut crab exoskeleton [25,26,37]. The step height (//x) corresponds to the Sh of the plywood structure.…”

Section: Fracture Surfacementioning

confidence: 99%

Tissue structure and mechanical properties of the exoskeleton of the huge claws of the mud crab, Scylla serrata

et al. 2023

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The mud crab, Scylla serrata, has huge claws in comparison with its body size. The color of the claw top’s finger surface changes from white to deep-mottled blue, and this discoloration was strongly associated with the change in hardness inside the finger cross section. With special attention to the discoloration points, the tissue structure of the exoskeleton was investigated via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction (XRD), and the mechanical properties were examined using Vickers hardness and nanoindentation tests. The exocuticle in the deep blue surface exoskeleton was as thin as that in other crustaceans, and the exoskeleton was occupied by the endocuticle with a twisted plywood structure. On the other hand, in the white surface exoskeleton, the thickness of the hard and dense exocuticle accounted for 52–59% of the exoskeleton thickness. This percentage increased at the claw tip. The hardness of the exocuticle was 2.5 times that of the endocuticle, and the microstructures and mechanical properties gradually varied at the boundary between the exo- and endocuticle. The mechanical properties were almost constant in the exocuticle, but calcium (Ca) concentrations decreased from the outer surface toward the boundary in that region and magnesium (Mg) concentrations increased. The change in the unit cell volume obtained via XRD suggested that some of the Ca atoms in the calcite crystal structure in that region were replaced with Mg atoms. Changes in crustacean coloration may help us to understand the tissue structure and mechanical properties within the exoskeleton. Graphical Abstract

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Section: Fracture Surfacementioning

confidence: 99%

Tissue structure and mechanical properties of the exoskeleton of the huge claws of the mud crab, Scylla serrata

et al. 2023

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“…The black spots in the endoC near the inner surface indicate pore canals (pcs). These black spots were also observed on the endoC on the outer side of the claw finger in the previous paper [14] and often can be observed on the polished surface of the exoskeleton with a TPS in crustaceans [1,18,20,23,26]. On the other hand, in Line G, shown in Figure 7, since the large denticle surface had a dense tissue structure, it was not possible to clearly observe the microstructure.…”

Section: Microstructurementioning

confidence: 70%

“…Here, the crystalline structures of the exoskeleton of the mud crab were calcite [14]. The minor components are found in the exoskeleton of the lobster, edible crab, and coconut crab [19,23,27]. The area scan results for inorganic matter (Ca, Mg, and P) for each site revealed differences in the compositions in the denticle, fingertip, and endoC.…”

Section: Chemical Compositionsmentioning

confidence: 84%

“…In sample 2, which has a large denticle, these pores appear as constrictions in the exoskeleton. The pores just below the denticle have also been observed in the coconut crab exoskeleton [20,23]. The results of the Vickers hardness test at characteristic sites for these four areas are represented in the table in Figure 2.…”

Section: Mechanical Propertiesmentioning

confidence: 87%

“…On the other hand, when a mud crab pinches a small prey such as a shellfish, which is its staple food, the denticles on the pinching side are the first point of contact and where a large force acts (Figure S1d). Unlike the case with the exoskeleton of the carapace and the outer side of the claws, there are few studies examining the microstructures and mechanical properties of the denticles of the pinching side [11,23]. In particular, in the case of the mud crab, denticles on the claw finger are characterized by being small (small denticles) at the fingertip and becoming larger (medium and large denticles) closer to the palm, as shown in Figure 1b.…”

Section: Introductionmentioning

confidence: 99%

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Mechanical Resistance and Tissue Structure of Claw Denticles of Various Sizes in the Mud Crab, Scylla serrata

2023

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Decapod crustaceans have tooth-like denticles on their claw fingers, which come into direct contact with predators and prey. Since the denticles are subject to more frequent and intense stress than other parts of the exoskeleton, they must be especially resistant to wear and abrasion. We clarified the mechanical resistance and tissue structure of the denticles arranged in a line on the fixed finger of the mud crab, which has huge claws. The denticles of the mud crab are small at the fingertip and become larger closer to the palm. The denticles have a twisted-plywood-pattern structure stacked parallel to the surface regardless of size, but the abrasion resistance strongly depends on the size of the denticles. Due to the dense tissue structure and calcification, the abrasion resistance increases as the denticle size increases, reaching its maximum at the denticle surface. The denticles of the mud crab have a tissue structure that prevents them from breaking when pinched. The high abrasion resistance of the large denticle surface is an essential feature for the frequent crushing of shellfish, which is the mud crab’s staple food. The characteristics and tissue structure of the claw denticles on the mud crab may provide ideas for developing stronger, tougher materials.

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Exoskeletal Trade-off between Claws and Carapace in Deep-sea Hydrothermal Vent Decapod Crustaceans

Cho,

Seo,

Hong

et al. 2023

Integrative and Comparative Biology

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Limitations on energetic resources create evolutionary trade-offs, prompting us to investigate if investment in claw strength remains consistent across crustaceans living in diverse habitats. Decapod crustaceans living in deep-sea hydrothermal vents are ideal for this study due to their extreme environment. In this study, we investigated whether decapods (blind crab Austinograea sp. and the squat lobster Munidopsis lauensis) living in deep-sea hydrothermal vents prioritize investing in strong claws compared to the carapace, like coastal decapods. We analyzed exoskeleton morphology, mechanical properties, structures, and elemental composition in both the carapace and claws of four Decapoda species (two each from Brachyura and Anomura infraorders) in vent and coastal habitats. Coastal decapods had approximately 4 to 9 times more teeth on their claw cutting edge than the vent species. Further, only the coastal species exhibited higher firmness in their claws than in their carapaces. Each infraorder controlled exoskeletal hardness differently: Brachyura changed the stacking height of the Bouligand structure, while Anomura regulated magnesium content in the exoskeleton. The vent decapods may prioritize strengthening their carapace over developing robust claws, allocating resources to adapt to the harsh conditions of deep-sea hydrothermal vents. This choice might enhance their survival in the extreme environment, where carapace strength is crucial for protecting internal organs from environmental factors, rather than relying on the powerful claws seen in coastal decapods for a competitive advantage.

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Columnar Structure of Claw Denticles in the Coconut Crab, Birgus latro

Cited by 6 publications

References 31 publications

Tissue structure and mechanical properties of the exoskeleton of the huge claws of the mud crab, Scylla serrata

Tissue structure and mechanical properties of the exoskeleton of the huge claws of the mud crab, Scylla serrata

Mechanical Resistance and Tissue Structure of Claw Denticles of Various Sizes in the Mud Crab, Scylla serrata

Exoskeletal Trade-off between Claws and Carapace in Deep-sea Hydrothermal Vent Decapod Crustaceans

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