Chitin and Hydroxyapatite - Chemicals for a Phenomenal Hammer

The peacock shrimp (Odontodactylus scyllarus) is an odd-looking creature with the amazing ability to use its extremely strong hammer claws and penetrate the shells of crabs and clams. How is it able to do this without injury? A lot of the claws' tough exterior is based on what it is made of - chitin and hydroxyapatite.

structure of chitin
("Chitin" by Dschanz - own work (drawn with BKchem). Licensed under Public Domain via Wikimedia Commons)

If you look closely at the bonds linking the two 6-membered rings, you see that they are connected by a 1,4-beta linkage (where C#1 of one ring is connected to C#4 of the other ring). The groups attached to the N atoms are acetyl groups, so these are known as N-acetyl groups.

With lots of O and N atoms around the polymer, there are many opportunities for hydrogen bonding, which lend to the strength of chitin.

 

structure of hydroxyapatite          Ca₅(PO₄)₃OH

Electrostatic forces of attraction between the ions of hydroxyapatite contribute to its hardness and is commonly found in tooth enamel.

For a cool video on how the peacock shrimp smashes with its hammer claws and a more detailed explanation, I highly recommend Destin Sandlin at Smarter Everyday.

 (By Jens Petersen (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons)

 

For more on the analysis and engineering of the hammer claw, here is a paper by James Weaver and co-authors:

The Stomatopod Dactyl Club: A Formidable Damage-Tolerant Biological Hammer