A new species of Navicula (Bacillariophyta) from the Niger River (Mali, West Africa)

Navicula suturata sp. nov. is described on the base of light and scanning electron microscopy observations of a sample, collected from the Niger River at Bamako, Mali. The species resembles four previously described taxa. Navicula suturata is morphologically most similar to N. nielsfogedii, but differs from it by larger valve dimensions and coarser areolae. The new species differs from N. venezuelensis by more convex valve margins, wider central area and higher striae density; from N. babeiensis by absence of external apical grooves, wider valves with coarser striation and finer areolation; from N. delicatilineolata by larger valve dimensions. A new morphological term, rimulae, is introduced for small shallow transapical cracks on the external surface of virgae and axial area.