Ecologically Driven Ultrastructural and Hydrodynamic Designs in Stomatopod Cuticles

Abstract

Ecological pressures and varied feeding behaviors in a multitude of organisms have necessitated the drive for adaptation. One such change is seen in the feeding appendages of stomatopods, a group of highly predatory marine crustaceans. Stomatopods include "spearers," who ambush and snare soft bodied prey, and "smashers," who bludgeon hard-shelled prey with a heavily mineralized club. The regional substructural complexity of the stomatopod dactyl club from the smashing predator Odontodactylus scyllarus represents a model system in the study of impact tolerant biominerals. The club consists of a highly mineralized impact region, a characteristic Bouligand architecture (common to arthropods), and a unique section of the club, the striated region, composed of highly aligned sheets of mineralized fibers. Detailed ultrastructural investigations of the striated region within O. scyllarus and a related species of spearing stomatopod, Lysiosquillina maculate show consistent organization of mineral and organic, but distinct differences in macro-scale architecture. Evidence is provided for the function and substructural exaptation of the striated region, which facilitated redeployment of a raptorial feeding appendage as a biological hammer. Moreover, given the need to accelerate underwater and "grab" or "smash" their prey, the spearer and smasher appendages are specifically designed with a significantly reduced drag force.

A highly aligned and mineralized structure is identified within the exocuticle of an impact-resistant crustacean appendage. This regional composite structure features circumferentially wrapped unidirectional chitinous fibers consisting of amorphous calcium carbonate and calcium phosphate that place the club under compression during high-energy strikes. Macro-morphological hydrodynamic features are revealed that significantly reduce drag, enabling acceleration to strike at incredibly high rates.

http://ift.tt/2B50dZ6