Compare Actinocyclus normanii

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Coscinodiscus curvatulus has a clearly visible pseudonodulus on the valve face and has areolae decreasing in size toward the valve margin. Actinocyclus subtilis has a prominent pseudonodule and has areolae arranged in incomplete, non-radiating, wavy rows. Thalassiosira baltica has only a single rimoportula, a double ring of marginal fultoportulae, and a flatter valve face.