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American Association for the Advancement of Science

This shrimp has a hammer

The stomatopods (Odontodactylus scyllarus) are an ancient group of marine tropical and subtropical crustaceans that are well known for their complex visual systems, solitary nature, and aggressive hunting strategies. Stomatopods' second pair of thoracic appendages are highly modified with hyper-mineralized hammer-like dactyl clubs for powerful close-range combat. This observation highlights the unique structure and impressive performance of this dactyl structure and the important lessons that can be learned from its investigation.
[Courtesy of S. Baron]

The hammer-like claws of the peacock mantis shrimp can smash through mollusk shells, the heads of small fish, even a glass aquarium wall. The claws themselves stay surprisingly strong, even after being damaged while delivering so many blows.

Scientists have now discovered what makes these claws so tough.

James Weaver of Harvard University and colleagues used specialized microscopes and other technologies to investigate the structure of the shrimp's claws down to a tiny scale.

They report that the claw has three regions, each with different material compositions and mechanical properties. The outer layer is dense with the hard mineral hydroxyapatite, which is also found in vertebrate bones and teeth. The layers behind it are less stiff, but they're constructed in a way that stops cracks from growing.

A better understanding of these claws and how they're built should help researchers develop tough materials for new types of body armor or other objects that must withstand intense, repetitive impacts.

The research appears in the 8 June 2012 issue of the journal Science.