Features of the Fine Structure and Si Content of the Mandibular Gnathobase of Four Freshwater Species of Epischura (copepoda: Calanoida)

The cutting edge of the mandibular gnathobase in many marine and some freshwater copepods is fortified with opal crowns for holding and grinding food. There is evidence of silica in these opal crowns for only seven species of freshwater copepods. Distinguishing characteristics of the structure and silicon (Si) content of the mandible's cutting edge were analysed in four species of Calanoida of one genus from two lakes in Russia (Epischura chankensis and E. baicalensis) and two lakes in North America (E. lacustris and E. nevadensis). The morphology of the mandibular gnathobase is described in detail for each species. Differences in the mandible characteristics and the level of crown silicification are observed within the genus Epischura. The highest content of silica is recorded in the crowns of E. baicalensis, which feeds on diatoms with thick frustules in Lake Baikal.