SEM images of species found in the transitional zone at Mykolaiv city (A, B, E–H valve views, C, D girdle views): A Minidiscus proschkinae with arrows showing rimoportula and marginal fultoportula B–D Skeletonema subsalsum with arrows showing marginal fultoportulae E Stephanodiscus hantzschii with arrow shown spines F Stephanodiscus makarovae with arrows showing marginal and central fultoportulae G, H Stephanodiscus minutulus with arrows showing spines and central fultoportula. Scale bars: 3 μm (A); 4 μm (B, F, H); 5 μm (C, D, G); 10 μm (E).