Mandibular Gnathobases of Marine Planktonic Copepods—Structural and Mechanical Challenges for Diatom Frustules

Copepods are dominant members of the marine zooplankton. Their diets often contain considerable proportions of diatomtaxa, many of which are known for superior mechanical properties of their mineralised frustules. Nevertheless, many copepod species are able to efficiently crush these frustules including rather stable ones. This ability very likely requires feeding tools with specific shapes, material compositions and material properties. When ingesting food, the copepods use the gnathobases of their mandibles to grab and, if necessary, crush and mince the food items. The morphology of these gnathobases is related to the diets of the copepods. Gnathobases of copepod species that mainly feed on phytoplankton feature compact and stable tooth-like structures, so-called teeth. In several copepod species these gnathobase teeth have been found to contain silica. Recent studies revealed the existence of complex composite structures that, in addition to silica, are composed of the soft and elastic protein resilin and form siliceous gnathobase teeth with a rubber-like bearing. These composite structures very probably increase the efficiency of the siliceous teeth while simultaneously reducing the risk of their mechanical damage. They are supposed to have coevolved with the diatom frustules in an evolutionary arms race, and their development might have contributed considerably to the dominance of copepods within today’s marine zooplankton.