Morphological study of Cyclotella distinguenda with a description of a new fossil species Cyclotella paradistinguenda sp. nov. from the Agios Floros fen, SW Peloponnese, Greece in relation to other Cyclotella species

Abstract

In a previous palaeoenvironmental study based on a high-resolution diatom record from a core sampled at the Agios Floros fen, SW Peloponnese, Greece, Cyclotella distinguenda was reported as exhibiting two morphs with distinct central area and stria arrangement, as well as a specific distribution throughout the sequence. In the present paper, we examine this morphological variability through detailed observations using light and scanning electron microscope combined with a simple statistical approach. Our new data suggest that the two morphs present substantial and constant differences in the structure and size of their central areas, the structure and number of their striae, the arrangement of their marginal fultoportulae/density of costae between fultoportulae, the shape of their rimoportulae and their alveolar chambers. On the basis of these morphological and stratigraphic variations one morph is described as a new species, Cyclotella paradistinguenda sp. nov., while the other is assigned to C. distinguenda and is also consistent with the original description of this taxon. The two species share well-defined central areas without fultoportulae, almost equal length striae and one rimoportula situated on a costa within the ring of marginal fultoportulae. Cyclotella paradistinguenda sp. nov. can be distinguished by a combination of the following characteristics: (1) large central area (≤1/3 of valve diameter), smooth or decorated with puncta and depressions, flat or concentrically undulated, (2) distinct, narrow striae (12–15/10 µm) consisting of one or two short rows of areolae of the same size expanding into three rows at the mantle, (3) marginal fultoportulae on each first to third costae (4) poorly developed alveolar chambers and rimoportula. Based on the stratigraphic distribution and the associated flora in the Agios Floros sequence, it can be inferred that C. paradistinguenda sp. nov. is tolerant of shallower water conditions with lower nutrient availability and/or higher pH than C. distinguenda.

Keywords:

• Cyclotella
• Cyclotella distinguenda
• Cyclotella paradistinguenda
• valve morphology
• SEM investigations
• palaeolake

Acknowledgments

We would like to thank Dr A.V. Karapanagiotou, Deputy Director at 38th Ephorate of Prehistoric and Classical Antiquities, Ministry of Culture and Sports and Dr E. Militsi, Director at 26th Ephorate of Byzantine Antiquities, Ministry of Culture and Sports for issuing permissions to visit and carry out sampling at the Agios Floros fen. We also thank Giorgos Maneas and Nikos Kalivitis for assisting during the field work planning and performance and Marianne Ahlbom for helping out with the performance of the SEM analysis at the department of Geological Sciences, Stockholm University. The study was conducted at the Department of Physical Geography and Department of Geological Sciences, Stockholm University, S-106 91 Stockholm, Sweden.

Additional information

Funding

This research was funded by the Swedish Research Council, Institute for Aegean Prehistory (INSTAP) and Navarino Environmental Observatory (NEO) under grant [621-2012-4344]. NEO is a partnership between Stockholm University, Academy of Athens and TEMES S.A., dedicated to research and education on the climate and environment in the Mediterranean region.