Showing posts from May, 2016

Diatom of the month – May 2016: Rhopalodia gibba

by Luca Marazzi* Rhopalodia gibba belongs to the epithemioid group , that is to say it has v alves symmetric about a line (bilateral symmetry), but asymmetrical to the apical (longitudinal) axis, the raphe system is well developed, enclosed within a canal, and positioned near the valve margin 1 . It is longer and more slender than other species such as the lunate R. gibberula , and the more arched R. musculus ; it is found in the benthos, attached to substrata such as plant (epiphytic), or gliding more freely and opportunistically 2 . Interestingly, R. gibba seems to have declined significantly in the United Kingdom due to agricultural intensification and associated large use of nitrogen fertilizers. In fact, t his pennate ( bilaterally symmetric) diatom species lives in nitrogen poor habitats, but it has evolved an endosymbiosis with cyanobacteria that fix nitrogen 3 . So it does not like when there is too much nitrogen around, and loses its competitive edge against other fellow