Rimocostatus bugojnicus gen.et. sp. nov. (Coscinodiscophyceae, Bacillariophyta) – a new fossil diatom genus from Gračanica, Bugojno palaeolake in Bosnia and Herzegovina
A new freshwater fossil diatom taxon Rimocostatus bugojnicus gen. et sp. nov, from Miocene sediments at the Gračanica site, Bugojno palaeolake in Bosnia and Herzegovina, is described. The main morphological feature of the genus is the presence of marginal rimoportulae with simple, round external openings positioned on interfascicles on the valve mantle and stalked, large, wide internal slits, positioned on every costa. Marginal and valve face fultoportulae are absent. With these characteristics, the species shows similarities to both marine and freshwater species, known from recent, and primarily from fossil, diatom deposits. Thus, Rimocostatus bugojnicus gen. et sp. nov. is an important find for understanding the evolution of centric diatom species.