New records of amphoroid diatoms ( Bacillariophyceae ) from Cachoeira River , Northeast Brazil Cavalcante , KP . * ,

Amphoroid taxa have been revised in recent decades. Many species formerly assigned to Amphora have been transferred to other recently proposed genera, as Seminavis (Naviculaceae) and Halamphora (Catenulaceae). In Brazil, there are few studies focused on amphoroid taxonomy. This study presents a taxonomic investigation of five uncommon amphoroid taxa from Brazilian diatom flora: Seminavis pusilla, S. strigosa, Amphora ectorii, Halamphora ghanensis and Halamphora sp. Seminavis strigosa is identical in valve morphology and morphometrical data to Amphora twenteana, and its synonymy is proposed. Seminavis pusilla, poorly found in Brazilian waters, has expanded its distribution. Halamphora ghanensis is a new record to American continent while Amphora ectorii are new to Brazilian aquatic systems. Halamphora sp. has distinct ultrastructural features in relation to similar species and is probably new for science.


Introduction
Dorsiventrality was considered a relevant character throughout the taxonomic history of the diatoms.However, it is known that this feature occurs in at least seven diatom orders and evolved apart many times along diatom evolution (Round et al., 1990).Amphoroid taxa are an artificial group characterized by strongly dorsiventral valve outline, that in the past were considered within the genus Amphora Ehrenberg (Levkov, 2009).The two valves of a frustule are not parallel in relation to apical plane, due to the girdle bands wider in dorsal side than in ventral one (Round et al., 1990).
In this context, Mann in Round et al. (1990) proposed the genus Seminavis Mann, based on old Amphora subgenus Cymbamphora Cleve, which was characterized by uniseriate striae, lineolate areolae, two plastids in unequal size and raphe structure similar to Navicula Bory stricto sensu.Seminavis was included in Naviculales, because of raphe and areolae structures more similar to members of this order, rather than valve strongly dorsiventral shared with Amphora.Thereafter, a number of papers have shown the morphology of former Amphora species, with transfers and new propositions to the genus Seminavis (Garcia-Baptista, 1993;Danielidis and Mann, 2002;2003;Danielidis et al., 2006;Garcia, 2007;Wachnicka and Gaiser, 2007).
Halamphora (Cleve) Levkov is another genus recently described, by splitting Amphora group, based on the presence of a single H-shaped plastid not extending to the dorsal girdle, raphe ledge in the dorsal side only, fused helictoglossa in proximal raphe endings and areolae internally occluded by hymenes and externally opened by simple foramina or complicated with short finger-like processes (Levkov, 2009).Nevertheless, there are still many Amphora species that needs further morphological studies to clarify their affiliations.
During a floristic survey performed in Cachoeira river, Northeast Brazil, two taxa belonging to Seminavis, one belonging to Amphora and two assigned to Halamphora were identified.The aim of this study is to describe them, comparing with allied species and documenting new records to Brazil and the Americas.

Material and Methods
The Cachoeira river is situated in the Eastern Basin, state of Bahia, Northeast Brazil.This coastal river is around 500 km long and has 4,600 km 2 of drainage area.Inserted into the Atlantic rainforest, it rises to 800 m elev., cover the major urban centers and flows onto the continental shelf of Ilhéus municipality.
Subsamples were cleaned with KMnO 4 and HCl, according to Simonsen' method (1974) modified by Moreira-Filho and Valente-Moreira (1981).Permanent slides were mounted with Naphrax® (R.I.=1.74).Diatoms were observed, measured and photographed at Olympus BX40 light microscope equipped with Differential Interference Contrast and Olympus DP71 digital imaging capture system.For Scanning Electron Microscopy (SEM) analyses, subsamples of cleaned valves were dried on stubs and covered with gold by sputter Balzers SCD030 and examined with a JEOL JSM 6360 at 15 kV, housed at the Electron Microscopy Center from the Federal University of Paraná, Brazil.

Order
Valve moderately dorsiventral, semi-lanceolate, with convex dorsal margin and straight ventral margin, slightly convex in central part; apices rounded, slightly ventrally curved; axial area narrow, central area asymmetrical, more expanded for the dorsal side; striae radiate, some shortened in the central area; areolae inconspicuous; raphe straight, proximal endings slightly expanded, distal endings inconspicuous.Length 22.7 mm, width 4.6 mm, 16 striae in 10 mm.
Taxonomic Remarks: historically, the taxonomy of this species has been confused.Cymbella pusilla Grunow is the original proposition.Krammer (1997) transferred it to the cymbelloid monospecific genus Navicella Krammer (a later homonym), after renamed Navicymbula Krammer (Krammer, 2003).This genus was characterized by a combination of dorsiventrality (related to cymbelloid taxa), areolae and raphe structures typical of Navicula sensu stricto, and ecological data.It was the single "Cymbella" that could occur in high salinity environments (Krammer, 2003).However, Krammer (2003) provided SEM images that already make clear that this taxon is assigned to Seminavis, which has priority.Finally, Cox and Reid (2004) transferred this species to the latter genus, based on cladistical analysis into Naviculineae.
Distribution: it is an unmistakably species, cosmopolitan and common in brackish and freshwater waters (Cleve, 1895;Krammer, 2003).In Brazil, Seminavis pusilla is rarely found and has been only recorded to São Paulo State (Tundisi and Hino, 1981;Ludwig, 1996).This is the first citation of species to northeast Brazilian system.
Seminavis strigosa (Hustedt)    Taxonomic Remarks: Seminavis strigosa and Amphora twenteana are two identical taxonomic entities that differ only in ecological aspects.Seminavis strigosa is characteristically from brackish environments while A. twenteana was described from freshwater (see distribution).In both species' protologues, there are no morphological features that allow a clear distinction between the two taxa.We realized that morphometric features known for both species are overlapping (Table 1).Specimens from this study were just slightly smaller than those showed by Hustedt (1949) and Danielidis and Mann (2003) but agree with specimens identified as A. twenteana (Krammer, 2003).You et al. (2008) registered longer and wider valves of A. twenteana, which overlap with Danielidis and Mann (2003) metrics.In all papers, illustrated individuals have identical valve outline, apices shape, central area and striae pattern.SEM illustrations showed similar morphology to those recorded in Danielidis and Mann (2003) for S. strigosa.Amphora twenteana have never been pictured in SEM but we believe that, in this case, the optical analysis would be enough to reveal a distinguishable feature.
We propose, therefore, the recognition of Amphora twenteana as later synonym of Seminavis strigosa, which has priority based on rules of botanical nomenclature.

Order Thalassiophysales D.G. Mann in
Distribution: it is reported to brackish/marine environments.The species is common in the type locality, Maracaibo Lagoon, Venezuela, attached to Potamogeton L. (Levkov, 2009).This is the first record in Brazilian waters.
Distribution: freshwater species of poorly known distribution.Recorded to Ghana, West Africa (Levkov, 2009).This is the first record to American continent.
Taxonomic Remarks: in LM, our taxon is similar to Amphora charrua Metzeltin, Lange-Bertalot et García-Rodrígues and Halamphora submontana (Hustedt) Levkov, being more closely related to Halamphora montana (Krasske) Levkov, with respect to measurements, shape of apices and central area (Levkov, 2009).However, by analyzing the SEM images, it is notable that our taxon does not agree with any of those species.Amphora charrua has not produced apices nor raphe ledge, and the morphology of areolae and raphe are clearly distinct; Halamphora montana has uniseriate striae on dorsal side near to raphe ledge, wide central area on dorsal side and higher striae density (40-45 in 10 mm); H. submontana has biseriate striae on dorsal side near to raphe ledge and central area on dorsal side is areolate, although the central striae are more spaced; however the striae density is higher (32-36 in 10 mm) and the areolae morphology on dorsal side is clear.
These findings indicate that our taxon is probably distinct from the species described in the literature.Unfortunately, we could not find more valves in SEM analysis, including internal views, due its rarity in the samples.In Halamphora, different species have also differences in internal structures.Under these conditions, the precise identity of this taxon is subject to further studies of its morphology by SEM.
Distribution: just found in samples from Cachoeira River, northeastern Brazil.
This study presented the descriptions of five uncommon amphoroid taxa from Brazilian diatom flora.Halamphora ghanensis had never been recorded to American continent while Amphora ectorii is new records to Brazilian aquatic systems.Additionally, Amphora twenteana is proposed as heterotypic synonym of Seminavis strigosa.Halamphora sp. has distinct ultrastructural features in relation of similar species and probably can be a new species for science.This data corroborate the need of more floristic diatom studies in Brazil, especially in unexplored environments, in order to reach a closer knowledge of the real diatom diversity that inhabit this extense country.

Table 1 .
Comparison between morphometric data of Seminavis strigosa and Amphora twenteana from this study and the literature.(*) indicate type material informations.
Round et al.Valve strongly dorsiventral, semi-lanceolate, with convex dorsal margin and slightly concave ventral margin, margins almost parallel in central part; apices acuminate; axial area narrow, biarcuate; central area broader on ventral side and linearly expanded on dorsal side; striae straight to radiate in dorsal side and radiate to convergent in ventral side; areolae inconspicuous; raphe strongly biarcuate; proximal endings dorsally oriented, distal endings inconspicuous.Length 24.6 mm, valve width 4.6 mm, frustule width 12.3 mm, 14 striae in 10 mm.