Morphological characterization of Skeletonema grevillei (Bacillariophyta, Thalassiosirales) in the Eastern Adriatic Sea

The present study shows the concise morphological description of Skeletonema grevillei Sarno & Zingone in the Sibenik Bay on the eastern coast of the Adriatic Sea. Increased abundance of the species was observed during January 2016. The scanning electron microscope (SEM) was used to detect the ultrastructural morphological features that distinguished the investigated species S. grevillei from the other species in the genus. The average diameter of the cell was 4.1 μm and the pervalvar axis of the valve was 2.2 μm. Intercalary fultoportula processes connecting two adjacent cells, formed a knuckle like junction that interlocked with one (1:1) and occasionally two (1:2) processes from the adjacent cell. Terminal fultoportula processes were open tubes, split along the entire length of the process, with irregularly truncated tips, which bore one or two small lateral spines. External processes of rimoportulae were short in the intercalary valves, but long in the terminal valves of the colony. The terminal rimoportula process had a truncated tip with a teapot spout-like end. The cingular band was composed of numerous copulae that had thin, transverse branching ribs, interspersed with 11-13 hyaline areas.