Encyonema exuberans sp. nov. (Bacillariophyceae) from southern Brazilian lotic systems
Tremarin, Priscila I.; Wetzel, Carlos E.; Ludwig, Thelma A.V.; Ector, Luc
Despite the relatively large number of species illustrated in the recent freshwater flora of South America, specific studies concerning cymbelloid taxa are still rare in the continent. The analysis of several samples collected in the southern region of Brazil (states of Paraná and Rio Grande do Sul) revealed the existence of an interesting Encyonema living in the epilithon of lotic environments. This paper describes and illustrates in detail the morphology of the new diatom Encyonema exuberans examined with light and scanning electron microscopy. Distinctive morphological features of this new species include valve shape, the strongly radiate and denser striation near the poles and the indistinct intermissio. The rostrate ends are always ventrally bent. The striae are composed of areolae with different sizes and shapes and are often uniseriate. Double rows of areolae are visible on the dorsal ends and near the raphe sternum. In external view, the central stria ends in a round stigmoid. The transapical dorsal ribs and the areolation patterns are a unique combination of features not known in any diatom belonging to the genus Encyonema, making them decisive taxonomic characters to distinguish this species within this genus.