Structure and mineralization of the spearing mantis shrimp (Stomatopoda; Lysiosquillina maculata) body and spike cuticles

Stomatopoda is a crustacean order including sophisticated predators called spearing and smashing mantis
shrimps that are separated from the well-studied Eumalacotraca since the Devonian. The spearing mantis shrimp
has developed a spiky dactyl capable of impaling fishes or crustaceans in a fraction of second. In this high velocity
hunting technique, the spikes undergo an intense mechanical constraint to which their exoskeleton (or
cuticle) has to be adapted. To better understand the spike cuticle internal architecture and composition, electron
microscopy, X-ray microanalysis and Raman spectroscopy were used on the spikes of 7 individuals (collected in
French Polynesia and Indonesia), but also on parts of the body cuticle that have less mechanical stress to bear. In
the body cuticle, several specificities linked to the group were found, allowing to determine the basic structure
from which the spike cuticle has evolved. Results also highlighted that the body cuticle of mantis shrimps could
be a model close to the ancestral arthropod cuticle by the aspect of its biological layers (epi- and procuticle
including exo- and endocuticle) as well as by the Ca-carbonate/phosphate mineral content of these layers. In
contrast, the spike cuticle exhibits a deeply modified organization in four functional regions overprinted on the
biological layers. Each of them has specific fibre arrangement or mineral content (fluorapatite, ACP or
phosphate-rich Ca-carbonate) and is thought to assume specific mechanical roles, conferring appropriate properties
on the entire spike. These results agree with an evolution of smashing mantis shrimps from primitive
stabbing/spearing shrimps, and thus also allowed a better understanding of the structural modifications
described in previous studies on the dactyl club of smashing mantis shrimps.