MORPHOLOGICAL STUDY OF THREE MARINE ARAPHID DIATOM SPECIES OF GRAMMATOPHORA EHRENBERG, WITH SPECIAL REFERENCE TO THE SEPTUM STRUCTURE

Three marine araphid diatoms species, Grammatophora angulosa Ehrenberg, G. arcuata Ehrenberg and G. hamulifera Kiltzing, were examined in light (LM) and scanning electron microscopy (SEM), including sections treated by a Focused-Ion-Beam system. Observations of sequential changes of septa morphology with cell size reduction revealed that a septum-body and a septum-base are connected at species-specific angle, θ, which can be used as the distinguishing character of each species under light microscopy (LM). θ is equal to ± a right angle for G. angulosa, to an obtuse angle for G. arcuata and to an acute angle for G. hamulifera. Observations of sections under SEM illustrated an interlocking mechanism of the pseudoseptum of a valve with a hooked part of a valvocopula. The presence of this physical interlocking system in G. angulosa and G hamulifera can be seen as a short, dark line between the valve and the valvocopula under LM, and is likely a sophisticated structure to keep the physical link between the valve and the valvocopula. The morphological features of three species under the LM and SEM are compared.