Morphological variation around the Pantocsekiella comensis complex in the Laurentian Great Lakes

Pantocsekiella comensis is ubiquitous in the Laurentian Great Lakes and is an important indicator of climate change and low nutrients. Pantocsekiella comensis forms a diverse complex with high morphological diversity. We distinguished three species within the complex: P. comensis, Pantocsekiella delicatula, and Pantocsekiella laurentiana sp. nov. by examining specimens from the Great Lakes using light and scanning electron microscopy. All species have radial, uniform, and alveolate striae, a central fultoportula, a rimoportula opposite the central fultoportula, and marginal fultoportulae. However, P. laurentiana has a smaller diameter than P. comensis (4–8 µm vs. 4–12 µm) and orbiculi depressi on half its tangentially undulated centre. Pantocsekiella delicatula has a distinct central fultoportula and colliculate centre, and lacks the orbiculi depressi and tangential undulation of P. comensis and P. laurentiana. Its diameter (4–14 µm) is generally larger than that of P. comensis. A multiple factor analysis based on morphological features, in addition to environmental characteristics, confirmed the separation of these species. The presence of transitional specimens with features of two or more of these species complicated classification; however, these occurrences were rare, and differentiation was usually possible.