Pseudostaurosira polonica is a poorly known small araphid species. The original type material seems no longer available. As the original description was based on fossils and eroded material, several important morphological features were only poorly documented. Therefore, an epitype is designated based on an Italian population from the small mountain tarn Lago di Valagola (Brenta Dolomites, Italy). LM and SEM observations of this population increased our knowledge of the morphology of this rarely observed species. These observations and comparison with Pseudostaurosira species showing a similar shape, indicated that at least two different morphological groups can be separated within the genus Pseudostaurosira. The analysis of this species also highlights the importance of a better conservation of original material in larger, well-curated collections.