Seminavis recta comb. nov. et stat. nov.: Morphology and distribution in salt marshes from southern Brazil

Abstract

Cymbella (Encyonema) grossestriata var. recta was studied based on analysis of the type material from Argentina and newly collected material from southern Brazil. In light microscopy the taxon presents dorsiventral valves, asymmetric and expanded central area, striae slightly radiate at the ends, becoming strongly radiate, and sigmoid in the center of valve. In scanning electron microscopy it is possible to observe features that are similar to the Navicula genus, such as slit-like areolae, accessory rib in the primary side, which is wider (expanded) at the center and valves with a marked virgae. Beyond these features the presence of two chloroplasts per cell definitively excludes the taxon from the Cymbellales group and allows us to transfer it to the genus Seminavis. Seminavis recta comb. et stat. nov. was found associated to Spartina and Scirpus species and living in the sediment of salt marshes in oligo to mesohaline zones, in a wide range of temperature and pH. This species is rare, and has been reported only to South America until now.