Epilithic diatoms (Bacillariophyceae) from running watersin NW Iberian Peninsula (Galicia, Spain) ; Diatomeas epilíticas (Bacillariophyceae) de los cursos de agua corriente del NO de la península ibérica (Galicia, España)

A catalog of Bacillariophyceae for the rivers of NW of Spain is made for the first time. It includes a re-examination of the taxa reported in previous publications, taxa cited during the last years of the rivers of the Galicia-Costa Hydrographic Demarcation, and a revision of the taxonomy, in line with the systematic and nomenclature changes, which have occurred mainly in recent years. The epilethic diatoms of the river basins of Galicia-Costa were sampled during the years 2005, 2006, and 2007, in May-June and September. The study was carried out in 41 localities distributed along 31 rivers, samples were taken in upstream and downstream sections. Diatom communities were compared in all upstream sections of these rivers draining from siliceous substrates. We identified 141 taxa of diatoms from the coast of Galicia. In this paper we present 15 new citations for Galicia, two for Spain and three for the Iberian Peninsula, in addition to a new species recently described. The dominant taxa are: Achnanthidium minutissimum, Achnanthes subhudsonis, Karayevia oblongella, Cocconeis placentula var. euglypta, Gomphonema rhombicum, and Navicula minima. Achnanthes subhudsonis was the most abundant species during the spring and summer months. The remaining species showed no relevant changes regardless of the time of year. The results indicate that the river diatoms of Galicia are an important component of the diversity of the ecosystem. Resumen. Se realiza por primera vez un catálogo de Bacillariophyceae para los ríos del NW de España. Se incluyen un nuevo examen de los táxones recogidos en publicaciones anteriores, datos de táxones citados durante los últimos años de los ríos de la demarcación hidrográfica de Galicia-Costa y una revisión de la taxonomía, en consonancia con los cambios sistemáticos y nomenclaturales, que se han producido sobre todo durante los últimos años. Se estudiaron las diatomeas epilíticas de las cuencas de los ríos de Galicia-Costa entre los años 2005, 2006 y 2007, durante dos temporadas diferentes: mayojunio y septiembre. El estudio se llevó a cabo en 41 localidades distribuidas a lo largo de 31 ríos, donde se tomaron muestras en tramos aguas arriba y aguas abajo. Las comunidades de diatomeas de estos ríos que drenan de sustratos silíceos fueron comparadas en todos los tramos de aguas arriba. Se identificaron 141 táxones de diatomeas de la costa de Galicia. En este trabajo presentamos 15 nuevas citas para Galicia, dos para España y tres para la Península Ibérica, además de una nueva especie recientemente descrita. Los táxones dominantes son: Achnanthidium minutissimum, Achnanthes subhudsonis, Karayevia oblongella, Cocconeis placentula var. euglypta, Gomphonema rhombicum, y Navicula minima. Achnanthes subhudsonis fue la especie más abundante durante los meses de primavera y verano. Las especies restantes no mostraron cambios pertinentes independientemente de la época del año. Los resultados indican que las diatomeas de los ríos de Galicia son un componente importante de la diversidad del ecosistema. Leira M., López-Rodríguez M.C. & Carballeira R. 2017. Epilithic diatoms (Bacillariophyceae) from running waters in NW Iberian Peninsula (Galicia, Spain). Anales Jard. Bot. Madrid 74 (2): e062. https://dx.doi.org/10.3989/ajbm.2421 Title in Spanish: Diatomeas epilíticas (Bacillariophyceae) de los cursos de agua corriente del NO de la península ibérica (Galicia, España). Received: 19‒VI‒2015; accepted: 29‒I‒2016; published online: 1-XII-2017; Associate Editor: A. Flores.


INTRODUCTION
Despite the fair and extensive floristic and taxonomic knowledge on the European freshwater diatoms, the diatom flora of the Iberian Peninsula is rather poorly known.The freshwater diatoms of Galicia -NW Spainhave never been thoroughly investigated and there are few works related to some selected localities.The first floristic studies on freshwater diatoms in the region date back to the first half of the 20 th century (Gamundi 1911) followed, already during the 50's, by those of Margalef (1955Margalef ( , 1956)).Later, Varela (1976Varela ( , 1982) ) made a major contribution, described several taxa with newer data, and published the only freshwater diatom catalogue of Galicia to the date (Varela & al. 1992).The last taxonomic studies of the diatom flora of Galicia have been published as restricted technical reports on water quality studies in lotic water systems (v.gr., Ector 1992;Penalta-Rodríguez & López-Rodríguez 2006;Delgado & al. 2010).Recently, a floristic account has been carried out in small upland streams from two zones catalogued as "site of communitarian importance" proposed by the local government in the Habitats Directive -92/43/EEC-of the Nature 2000 Network (López-Rodríguez & Penalta-Rodríguez 2007;Penalta-Rodríguez & López-Rodríguez 2007).Other more ecologically or paleoecologically orientated publications Epilithic diatoms (Bacillariophyceae) from running waters in NW Iberian Peninsula (Galicia, Spain) include Bao & al. (2007).However, despite this growing number of diatom studies in this area, the freshwater diatom flora of Galicia remains rather poorly known.Under these circumstances there is still a need of collecting more data on their distribution and ecological preferences.
This paper reports the results of a systematic survey of the diatom assemblages in Galicia -NW Spain-.The paper describes diatoms collected from running waters in rivers and streams of the Galicia-Costa basin.The study has three main goals: 1) to present a floristic catalogue of the freshwater diatoms living in the rivers of the study area; 2) to provide data on their distribution and autoecology; and 3) to give descriptions of unusual taxa.

Study Area
Galicia is located in the NW of Iberian Peninsula, situated in a transitory zone between the Atlantic and Mediterranean regions under an oceanic climate (fig.1).The geology is dominated by siliceous rocks: granite in the west and metamorphic rocks in the east.The topography of the area consists mainly of granite rocks, where hills alternate with valleys.The mountain ranges are of low altitude -between 800 and 1,000 m a.s.l.-.The Galician relief is complex and clearly characterised by the presence of steep slopes.
One of the key elements of the Galician landscape is the existence of a large and dense river network controlled by climate and tectonic and the morphological configuration.Galicia-Costa has mild winters and cool summers with precipitation exceeding 1,500 mm per year while well distributed throughout the year.As a result most of the Galician rivers have an Atlantic or oceanic climate characterized by an abundant and regular flow, with high waters in winter and a moderate drought in the summer.The mountainous geomorphology and regular precipitation influences the occurrence and permanence of many small and medium-sized rivers with regular discharge throughout the year.
The river systems occurring within the area of Galicia-Costa include all Galician river basins that flow into the Bay of Biscay and to the Atlantic Ocean.The rivers of the Bay of Biscay slope flow to the north.These rivers are short with steep gradients.These rivers undergo an oceanic climate with a reduced variation in annual temperature and rain patterns.The Atlantic slope comprises all the rivers flowing west to the Atlantic Ocean.These rivers show a higher environmental and spatial variability, with two groups easily differentiated: the rivers of the Arco Ártabro-Fisterra and the rivers of the Rias Baixas.The proximity of the mountains to the coast and the oceanic climate of the basins of the Arco Ártabro-Fisterra make all rivers in this area short and quite fast flowing, although they have a summer drought more pronounced than those of the Bay of Biscay.The Rías Baixas rivers are subject to significant Mediterranean influences and undergo severe droughts during summer months.

Sample Collection
This study was carried out in 41 localities (fig. 1) distributed along 28 rivers in the Galicia-Costa River District.The study has been completed with the inclusion of seven high altitude sites from the mountain ranges of the Macizo Central Gallego (MCG), located in the SE of the studied area.The rivers have been grouped in the five different geographical areas described above according to their drainage basin.
Localities were sampled between 2002 and 2007 at different moments of the year but more frequently at the end of spring and summer.Diatoms were collected with a brush, from medium-size stones chosen from well lightened and flowing streams.Samples were preserved in a cool-box in the field, until being carried to the laboratory.Diatoms frustules were cleaned with 30% H 2 O 2 in hot during 6-7 h.The cleaned frustules were mounted on glass-slides using Naphrax ® (CEN 2003(CEN , 2004)).Identification of the species was carried using an Olympus BX61 microscope equipped with differential interference contrast -DIC, Nomarski-under 1,000× magnification.A minimum of 400 valves were counted whenever possible.In most cases diatoms were identified to the species level following standard literature (Krammer & Lange-Bertalot 1985, 1988, 1991a, 1991b) supplemented by more specific works (Krammer 1997a(Krammer , 1997b(Krammer , 2000(Krammer , 2002(Krammer , 2003;;Lange-Bertalot & Metzeltin 1996;Lange-Bertalot 1999, 2001;Lange-Bertalot & Krammer 1989;Reichardt 1999;Lange-Bertalot & al. 2011).Additionally, previous references for the Iberian Peninsula were checked after Aboal & al. (2003).Information about the global distribution and taxonomic status of species recorded during the survey was taken from AlgaeBase (Guiry & Guiry 2015).
Weighted averaging regression and calibration were perfomed to calculate pH, conductivity, nitrates and phosphates optima of diatom species using the computer program C2 (Juggins 2014).Estimates of optima were assessed comparing the root mean square of prediction -RMSE-and the bootstrap RMSE.

RESULTS AND DISCUSSION
Characteristics of studied localities are given in table 1: temperature -ºC-, pH, conductivity -µS•cm -1 -, dissolved oxygen -mg•L -1 -, water hardness -mg CO 3 Ca •L -1 -, and catchment area.The majority of the study sites were situated below 20 m a.s.l., and eight sites occurred between 200-350 m a.s.l.Water temperature ranged from 13.3 ºC to 22.4 ºC among sites within the same sampling season.On average, water temperature varied between 13-20.1 ºC across sites regardless of their altitude.pH values varied slightly between 6.2 and 7.6.Ten sites showed slightly acidic conditions with a mean pH between 6.2 and 6.9.Conductivity values ranged from 35 to 457 µS•cm -1 , with only two localities with values above 200 µS•cm -1 .Sites are typically acidic with low alkalinity levels.
Results of the diatom analysis are divided into three parts.First, we provide a narrative on some taxa and their distribution to examine relationships between the occurrences of diatom taxa.Second, we establish a provisional taxon checklist for Galicia freshwater diatoms.Finally we give an account of unusual taxa with distribution restricted mostly to Galicia or northwest Iberia.
Galicia river diatoms are a diverse component of the ecosystem, although very distinctive of the Iberian Peninsula diatom flora.Compared with some other geographically and climatically similar areas in northern Spain, Galician running waters are quite distinctive.The geology in the Galician coastal area is homogeneously siliceous, thus rivers and streams are characteristically softwater.Consequently, diatom taxa characteristic of acidic waters were usually well-represented in Galician rivers (table 2).Taxa belonging to the genus Eunotia together with Navicula angusta, Peronia fibula, and Surirella roba were common components of the diatom community throughout all the studied area, although in low numbers.Diatom communities showed a high degree of similarity among sites and were comparable in all upstream stretches of these rivers draining siliceous substrates.Dominant epilithic diatom taxa were Achnanthidium minutissimum, Achnanthes subhudsonis, Karayevia oblongella, Cocconeis placentula var.euglypta, Gomphonema rhombicum, and Navicula minima.Achnanthes subhudsonis was the most abundant species during the spring and summer months.The remaining species showed no relevant changes regardless of the time of year.Other species which also occurred frequently but were less abundant were: Amphora pediculus, Cocconeis placentula var.pseudolineata, Encyonema minutum, Fragilaria capucina subsp.rumpens, Gomphonema parvulum, Melosira varians, Navicula angusta, Navicula cryptocephala, Navicula cryptotenella, Navicula lanceolata, Navicula minima, Navicula rhyncocephala, Nitzschia dissipata, Nitzschia palea, Planothidium lanceolatum, Psammothidium subatomoides, Ulnaria ulna, and Ulnaria biceps.
Overall, 141 taxa have been found which can be classified in 48 genera and six families.The taxa that are new records for Iberian Peninsula are marked with three asterisk (***), for Spain with two asterisk (**), the records which are new to Galicia with an asterisk (*).Locality numbers for the new records and figures are indicated after each taxon within brackets.Description of selected taxa 1. Achnanthes brevipes var.intermedia (Kütz.)Cleve, Kongl. Svenska Vetensk.-Akad. Handl. ser. 4, 27(3): 193 (1895).Fig. 4o.
Valves 14-130 × 9.5-40 μm, linear-lanceolate or linearelliptical to elliptical, with wedge-shaped or obtuse to broadly rounded endings, often a bit concave in the middle.Raphid valves with a moderately strong to weak curved raphe and equilateral-turning terminal branches.Axial area narrow, linear, while central area is fairly narrow, reaching to the edges forming a transverse fascia.Rapheless valves with narrow axial area, often running curved, mostly.Ends not wedge-shaped, but rather broadly rounded.Stria mostly 9-10 in 10 μm and less coarse than Achnanthes brevipes C.Agardh.
Habitat and distribution.-Thisspecies has a cosmopolitan distribution along lowland areas even in estuaries.Hustedt (1930) thought that it could be regarded as caused by reduced salinity variation.
Valves 25-33 × 5-6.5 μm, outline very variable, strictly lanceolate, although gradually narrowing early to almost pointed ends.Striae 26-30 in 10 µm, mostly from two to three composed lineolae, radial, and only at the ends sometimes parallel to slightly convergent.The Voigt unconformity is clearly visible on one side by truncated stria.Central area is small and indistinct rhombic, and clearly separated from the narrow linear axial area.Raphe filiform with small, clearly marked central pores.distribution of this taxon in Europe is not known precisely because of the confussion with Brachysira brebissonii.
Valves 110-200 × 26-35 μm, moderately to distinctly dorsiventral, dorsal margin evenly arched.Ventral margin slightly protuberant at the central part.Valve ends not protracted and broadly rounded.Axial area moderately wide, linear, widening at mid-valve to form a widened central area.Raphe filiform near the proximal ends with moderately large roundish central pores which are moderately distant and slightly ventrally deflected.Distal ends slightly reverse-lateral, terminal fissures sickleshaped.Striae slightly radiate.Puncta distinctly visible and more or less roundish.Striae 6.5-8 in 10 μm.
Habitat and distribution.-Althoughwidely distributed in Europe, it is not often recorded in large numbers.It prefers oligotrophic waters, especially favoured are habitats in the mountains of average electrolyte content.

Eunotia faba
Valves are asymmetric to the apical axis and variably asymmetric to the transapical axis.Dorsal margins are moderately arched.Ventral margins are weakly concave.The apices are broadly rounded, with a deep notch on the ventral side.Terminal raphe fissures are very short at the junction of the valve face and mantle.Striae are radiate and very finely punctate.Areolae are difficult to resolve in LM.
Habitat and distribution.-InEurope Eunotia faba was found in Ireland, Wales and Romania from soft, somewhat dystrophic ponds, lakes and swamps.Camburn & Charles (2000) reported this taxon -as Eunotia vanheurckii R.M.Patrick-from low-alkalinity lakes in the Adirondack Mountains of New York.Eunotia faba has been recorded from in anthropogenically undisturbed oligotrophic, weakly acidic to alkaline habitats in mountainous areas (Lange-Bertalot & al. 2011).
Note.-A similar taxon is Eunotia incisa that has acutely rounded apices and narrower valves -less than 5 µm wide-.Eunotia rhomboidea Hustedt is also heteropolar, or asymmetric to the transverse axis, but Eunotia faba has distinctly wider valves.Nörpel, Alles & Lange-Bert., Nova Hedwigia 53: 206 (1991).Valves 20-40 × 3-6 μm.Ventral margin is weakly concave, while dorsal margin is distinctly convex.Frequently, this dorsal margin presents two shallow undulations.Valve somewhat narrower at the ends than at the centre.The ends of the valve are rounded, narrowing slightly but they do not set off from the main body of the valve.The terminal nodes are located near but not at the end of the valve.Striae in the middle around 14-16 in 10 μm, about 22 in the ends; striae straight and almost perpendicular to the ventral side in the center of the valve.

Eunotia implicata
Habitat and distribution.-Thistaxon is fairly common in silicatedominated streams of the highlands and the North German lowlands, occurring even at high numbers, but rarely observed in stagnant water (Hoffman & al. 2013).The habitats are largely anthropogenically undisturbed, low in electrolytes and oligotrophic to dystrophic.Ortiz-Lerín & Jaume Cambra (2007) reported this taxon from low to upland streams in Northern Spain -76-1,356 m a.s.l.-with pH = 4.3-7.9 and conductivity ranging from 4.17 to 720 μS•cm -1 .Eunotia implicata is an acidophilus taxon, mainly occurring at pH below 7 (Van Damm & al. 1994).In this work Eunotia implicata has a pH optimum of 6.3 and was found in oligotrophic lowland streams.
Valves 15-50 × 4-7 μm.Striae 13-17 in 10 μm, more distant at the centre of the valve than at the ends.Ventral margin straight in smaller specimens but weakly concave in larger specimens.Dorsal margin is convex.Apices are acutely rounded, with a "nose-like" appearance.Raphe distal ends lie on the valve mantle and the terminal raphe nodules are well set in from the apices.Frustules are rectangular to quadratic in girdle view.
Valves 14-45 × 3.5-5 μm, thickened midway between the center and the ends.Striae 14-19 in 10 μm, getting closer to the ends.The ventral side of the valve is almost straight or weakly concave at most.The dorsal margin is convex.The apices hardly differ from the body of the valve.The terminal nodes are clearly differentiated, and located near the ends.
Habitat and distribution.-Spread,so far known with certainty only from the northern hemisphere, scattered in the area, mostly occurring in poor populations.Ortíz-Lerín & Cambra (2007) found this taxon in habitats with pH 5.4-7.3, and low conductivity -17.6-112 μS•cm -1 -in mid-altitude sites -205-1,086 m a.s.l.-.Acidophilus, mainly occurring at pH below 7 (Van Damm & al. 1994).In the studied area the species has a pH optimum of 6.2.
Note.-Similar outline to Eunotia faba.However the location of the terminal nodes is different.
Valves 10-140 × 5-10 μm, dorsiventral and symmetric to the transapical axis.Striae 7-15 in 10 μm, extending across the entire surface of the valve.Ventral margin straight or slightly concave, can appear biarcuate due to inflated central region.The apices of the valves have a rounded end.Raphe runs mainly on the valve mantle and at the poles and it is curved slightly over the face of the valve at the apices.Terminal nodes are clearly distinctive.Rectangular frustules in girdle view.
Habitat and distribution.-Thistaxon is not very well represented in this region, it was found only in six sites with low abundance.Often in circumneutral to weakly acidic, low conductivity waters (Patrick & Reimer 1966).
Note.-This variety of Eunotia pectinalis has many, slight undulations along the dorsal margin and a central swelling to the ventral margin.These characters are used to distinguish the variety Eunotia pectinalis var.undulata from its nominate variety (Patrick & Reimer 1966;Krammer & Lange-Bertalot 1991) Valves 20-100 × 4-15 μm.Striae at mid-valve 6-13 in 10 μm, irregularly and distantly spaced, and slightly more dense at valve ends, parallel, becoming strongly radiate at valve apices.Valves weakly to strongly curved with clearly protracted, broadly rostrate or abruptly terminated ends.The dorsal margin is convex; narrowed, and the ends are truncate-rostrate.The terminal nodules are distinct, at the ends of the valve, extending upwards along the apices.The frustles in the girdle view are rectangular.

Eunotia subarcuatoides
Valves 6-35(40) × 2.7-4.5 μm, curved dorsiventrally and symmetric to the transapical axis.Dorsal margin consistently strongly convex, smooth, rarely linear.Ventral valve margin consistently weakly concave.Valve slightly narrowed towards the end.Apices rounded to slightly (sub-) rostrate.Striae 18-23 in 10 μm, extending across the entire valve face.Raphe slightly developed mainly on the valve mantle and restricted to the poles.Terminal nodules small, dot-like, positioned slightly distant from both valve apices M. Leira & al. 20 and ventral valve margin.Frustules box-like or rectangular in girdle view.Raphe often only visible in girdle view.
Habitat and distribution.-It is a common diatom in Galicia rivers occuring in high abundance.Its highest abundance was at pH 6.1.Eunotia subarcuatoides has been classified as an acidobiontic with an optimal occurrence at pH < 5.5 (Van Damm & al. 1994).Anyway, it seems to tolerate high and strong variations of pH values (Alles & al. 1991 Arch. Hydrobiol. 19: 510 (1928).Fig. 5i.
Valves 28-105 × 10-18 μm, generally rhomboid in shape, although valves at the small end of the size range are not strongly rhomboid.Striae 29-32/10 μm, parallel in the middle to gradually strongly convergent to the end, radiate at the apices; longitudinal striae are present, but may be disorganized at the valve center.The apices are slightly constricted and narrowly rounded.The longitudinal ribs are slightly curved.Both the thickness of the ribs and size of the central nodule are variable in relation to valve size.The porte-crayon is relatively small.
Habitat and distribution.-This is a characteristic species from dystrophic and low-electrolyte waters.Indicator of high ecological quality.
Note.-Frustulia crassinervia (Bréb.)Lange-Bert.& Krammer has prominently undulate valve margins, while the margins of Frustulia inculta P.Siver, J.Pelczar & P.Ham.are very slighty undulate.In addition, the valve margins of Frustulia crassinervia are more strongly undulate and its apices more narrowly protracted than those in Frustulia saxonica.Bert., Iconogr. Diatomol. 2: 45 (1996) Valves 6-14 × 4-5 μm, elliptical in the smaller specimens and linear in the larger, and centrally inflated.Striae 24-30 in 10 μm.Flat valves with large sternum raphe, and two rows of elongated areolae that are only visible in LM.A longitudinal row of areolae runs over the mantle along the margin of the valve, interrupted at the ends.
Habitat and distribution.-Humidophilaperpusilla is a widespread diatom common in silicate dominated waters in highlands.It has also been cited from aerial habitats and often occurring in association with Diadesmis contenta (Grunow) D.G.Mann.Characteristic are also habitats with reduced light intensity such as caves and rock crevices.The freshwater genus Humidophila Lowe & al. is typically restricted to subaerial habitats (Round & al. 1990).In our study, Humidophila perpusilla was found in poor electrolyte, circumneutral and oligotrophic waters.

Naviculadicta langebertalotii
Valves 12-26 × 4.5-5.5 μm.Striae 16-23 in 10 μm, parallel in the central part, soon becoming moderately radial, becoming parallel again towards the apices.Raphe branches straight, filiform; central endings only very slightly bent; proximal raphe ends relatively close to each other, and only very slightly bent in the same direction which is opposite to that one towards which the terminal fissures are curved.Faint longitudinal lines visible on both sides of the raphe.Axial area narrow and straight, slightly widening towards the central area that is just a small unilateral expansion of the axial area.
Habitat and distribution.-Thetype locality -Soutomaior, at the River Verdugo-is a low altitude -140 m a.s.l.-stream stretch located in a narrow valley with steep slopes.The river bed is dominated by hard geological substrata, such as granites and phyllites.This species is typical of low-conductivity, meso-eutrophic, slightly-acidic but nonacidified, running-water sites, that reaches maximum relative abundances in autumn.Habitat and distribution.-Iconellalinearis is considered a cosmopolitan species, common in slightly acidic to neutral pH, weakly to moderately mineralized and moderately impacted by organic matter and nutrients.
Note.-Also transferred into genus Iconella by Ruck & al. (2016).Very similar to Surirella roba Leclercq but Iconella linearis has a larger size and coarser structure, with more distantly spaced fibulae and corrugations.

Fig. 1 .
Fig. 1.Map of Galicia sampling sites studied.Sites numbered from 1 to 34 are those included within the Galicia-Costa basins (HDGC).The Macizo Central Gallego (MCG) localities are numbered from 35 to 41.

Table 1 .
Localities and physicochemical values.[C,rivers of the Bay of Biscay; AAF, rivers of the Arco Ártabro-Fisterra; ARB, rivers of the Rias Baixas; MCG, rivers of the Macizo CentralGallego.]

Table 2 .
Optima calculated for the most common and abundant diatoms.Values were calculated using Weighted Averages as implemented in C2 (Juggins 2014).
Epilithic diatoms from running waters in NW Iberian Peninsula 19 Anales del Jardín Botánico de Madrid 74 (2): e059.https://dx.doi.org/10.3989/ajbm.2421Note.-Several forms and variations in length, width, and stria density are currently included in the broad concept of Eunotia incisa.Lange-Bertalot & al. (2011) have further described new species from Europe, such as Eunotia incisadistans Lange-Bert.& Sienkiewicz, which has broader valves with lower stria density.Eunotia incisa is also similar to Eunotia boreoalpina Lange-Bert.& Nörpel-Schempp and Eunotia rhomboidea Hust.only in girdle view.Eunotia veneris (Kütz.)De Toni was often confused in the older literature and is not detected in Central Europe.Valves of Eunotia incisa, however, are symmetric in regard to apex width and position of the helictoglossae compared to the asymmetry in these features in Eunotia rhomboidea.In North America, more differentiable taxa occur.Eunotia incisa is similar to Eunotia canicula P.C.Furey, R.L.Lowe & J.R.Johans.and the size range of the two species overlap.The apices of Eunotia incisa, however, are more nose-like than the apices of Eunotia canicula.Furthermore, the valves of Eunotia canicula are narrower and the helicotoglossae are closer to the apex -less inset-as compared to Eunotia incisa.Individuals such as those in fig.61 that have broader and rounded apices, such as valves with morphology similar to Taf. 161 figs.13-15 in Krammer & Lange-Bertalot (1991) could be considered as a new species, although for the moment they should be considered only as another variation of valve morphology.7. Eunotia intermedia (Krasske ex Hust.)Nörpel &