Abstract
The species originally described from brackish waters of the Venetian Lagoon as Nitzschia persuadens is a diatom rarely cited in the literature since its proposition and it is here recorded for the first time in a freshwater environment in South America. Morphological features of this species, such valve slightly panduriform, with a longitudinal straight fold of the valve face, poroidal areolae, and strongly eccentric raphe system clearly assign this species to Tryblionella, and the transfer was made. Here we present new observations on the frustule morphology and comparisons with related species. Light and scanning electron microscopy data of Tryblionella persuadens comb. nov. from Cachoeira River, Northeastern Brazil are documented.
Highlights
The distinction among Tryblionella, Psammodictyon and Nitzschia sensu stricto is given by a combination of diagnostic features, based on valve, raphe and fibula structures
Very eccentric raphe system accompanied by a longitudinal straight fold of the valve face is useful to Tryblionella affiliation (Mann 1978)
Cholnoky (1961) have already noted that T. persuadens should be included in this group
Summary
Smith is a widespread epipelic genus, occurring in marine, brackish or high conductivity freshwaters (Round et al 1990). This taxon was erected to generic status by Round et al (1990), grouping the species included in four old sections from Nitzschia Hassal: Tryblionellae (W Smith) Grunow, Circumsutae Grunow, Apiculatae Grunow and Pseudotryblionella Grunow. This proposition have not been adopted by all diatomists, who considered unclear the selected discriminating criteria established (Witkowski et al 2004). Whereas classification must be consistent with the phylogenetic relationships among groups, molecular tools combined with morphological features based on frustule, life form and plastids position (see Mann 1978) should clarify the genera consistency and their affiliations
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