Naviculadicta langebertalotii sp. nov. (Bacillariophyta) from streams in Galicia (N-W Spain

Naviculadicta langebertalotii sp. nov. (Bacillariophyta) from streams in Galicia (N-W Spain
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  Nova Hedwigia, Beiheft 141, 71–80 Article Stuttgart, März 2012 © 2012 J. Cramer in Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany  1438-9134/2012/0141 - 0071 $ 1.25  Naviculadicta langebertalotii   sp. nov. (Bacillariophyta) from streams in Galicia (N-W Spain) Marco Cantonati*  1 , Manel Leira 2 , Nicola Angeli 1  and Carmen López Rodríguez 3 1  Museo delle Scienze, Limnology and Phycology Section, Via Calepina 14, 38122 Trento, Italy 2  Universidad de A Coruña, Facultad de Ciencias, Campus de A Zapateira, 15071 A Coruña, Spain 3  Universidad de Santiago de Compostela, Department of Botany, Biology Faculty, 15075 Santiago de Compostela, Spain.* Corresponding author: With 3 figures and 2 tables Abstract : A new benthic freshwater diatom,  Naviculadicta langebertalotii  sp. nov., is described on the basis of light and scanning electron microscope observations as well as on its ecological preferences as reconstructed from data collected in the field. The most characteristic morphological features are the valve outline (elliptical, but with lateral margins that are frequently concave causing the outline to tend to a panduriform shape), longitudinal lines due to more marked and/or transapically elongated areolae on both sides of the raphe, and the hooked terminal raphe endings confined on the valve face (SEM). The new spe-cies so far was found on stones in meso- /eutrophic, slightly acidic (but not acidified) soft-water streams of Galicia (north-western Spain). Since its morphological characteristic did not correspond to any of the genera defined within  Navicula  sensu lato, the new species had provisionally to be assigned to the genus  Naviculadicta  Lange-Bertalot. Key words :  Naviculadicta ;  Naviculadicta langebertalotii sp. nov .,  diatoms, epilithon, streams, Galicia, siliceous substrata Introduction Diatoms are extremely-suitable organisms for a variety of research and applied purposes (e.g., Stoermer & Smol 2010). Among these, environmental assessments and monitoring programmes are of great importance (Ector et al. 2004). In Europe, many efforts were and are being done to promote, improve, simplify, and harmonize (e.g., Kahlert et al. 2009) the use of diatoms for the bioassessment of lotic and lentic bodies of water, in particular to improve the application of the Water Framework Directive (European Union 2000). The symposia “Use of algae for monitor-ing rivers” have been since 1991 (Whitton et al. 1991) and still are (Ector et al. in prep.) an important occasion of debate and exchange of experiences on the use of diatoms for monitoring eschweizerbart_xxx  72M. Cantonati et al. rivers. One of the key points is the spreading of the use of updated and detailed taxonomy (see e.g., Hlúbikova et al. 2011 for  Achnanthidium ), or, at least, consistent (e.g., Lange-Bertalot 1997) nomenclature and criteria. To reach this goal, several taxa that are encountered during routine sampling and that cannot be reliably identified have to be worked up taxonomically and charac-terized from an ecological point of view. Medium and small naviculoid taxa are very common and widespread, and can often be difficult to identify correctly.During most of the 20 th  century the genus  Navicula  was defined very broadly, and kept as collecting genus ( Sammelgattung ) for practical reasons (compare Krammer & Lange-Bertalot 1997), in spite of the fact that, since several decades, its very heterogeneous nature was becom-ing increasingly evident. In the last decade of the 20 th  century  Navicula  sensu lato began to be splitted, with the groups of species with the most peculiar combinations of characteristics being recognized and published as new genera (e.g., Round et al. 1990).  Navicula  was consequently re-defined (compare, e.g., Lange-Bertalot 2001) in the much narrower srcinal sense:  Navicula  sensu stricto, i.e.  Navicula  Bory de St. Vincent 1822, to include naviculoid taxa with an alveolate system of costae and with the alveoli including mostly-lineolate areolae [conforming to the gene-ritype species  Navicula tripunctata (O. F. Müller) Bory]. This arose the practical problem of how to deal taxonomically with the many naviculoid taxa not conforming to  Navicula  sensu stricto. As an empirical, nomenclatural solution, Lange-Bertalot proposed the erection of a new genus  Naviculadicta  Lange-Bertalot (in Lange-Bertalot & Moser 1994) to accommodate all naviculoid taxa with character combinations not corresponding to  Navicula  sensu stricto or to any of the genera newly recognized and defined within  Navicula  sensu lato.  Naviculadicta is conceived to accommodate species in a provisional way, until the naviculoid genera they belong to will be recognized and established, and is therefore, by definition, an “unnatural” and heterogeneous taxon (Kociolek 1996).During the taxonomic screening of materials sampled from streams in Galicia (Spain), a rela-tively small naviculoid diatom that couldn’t be assigned to  Navicula  sensu stricto or to any of the genera newly recognized and defined within  Navicula  sensu lato was found. Further, LM and SEM work and the careful examination of the environmental characteristics of the sites where this diatom was found allowed us to conclude that the taxon had distinctive morphological and ecological features differentiating it from the other known species. The taxon is therefore hereby described and characterized as a species new to science. Methods In the Galicia-Costa watershed district (north-western Spain), 34 localities distributed along 28 rivers were sampled. The study was completed with the inclusion of eight high-altitude sites from the mountain ranges of the Macizo Central Galego and Serra Enciña da Lastra, located in the South-East of Galicia. Localities were sampled between 2002 and 2007 at different moments of the year but more frequently during spring and autumn. Sampling and counting followed CEN standards (2003, 2004). At least five cobbles or small boulders were randomly collected from the stream bottom in riffle sections. Biofilms and covers were removed with a toothbrush to detach the algal communities to a final area of 2 –10 cm 2 . Algal samples were preserved in formaldehyde 4 % until analysis. Diatoms frustules were cleaned with 30 % (v/v) H 2 O 2 in hot during 6 –7 hours. The cleaned frustules were mounted on glass-slides using Naphrax ® . Several environmental vari-ables were measured simultaneously to the diatom sampling. Temperature, pH, conductivity and dissolved oxygen were measured “in situ” in each locality with a HANNA HI 9024 C microcom-puter pH meter, a HANNA HI 9033 multi-range conductivity meter and a CRISON oxi 45 oxy-meter. Water samples for chemical analyses were collected into polypropylene bottles and trans-ported chilled to the laboratory. The analyzed chemical parameters included those characterizing the geochemistry of the waters (alkalinity, Ca 2+ , SiO 2 , Mg 2+ , Na + , Cl – , SO 42- ), and those directly eschweizerbart_xxx  73 Naviculadicta langebertalotii   sp. nov. affecting the diatom composition and biomass (NH 4+ -N, PO 43- -P, NO 3- -N). Standard methods for chemical water analysis were followed (American Public Health Association, APHA, AWWA & WEF 1995). Physiographical variables and some basin characteristics were GIS derived from the 1993 CORINE Land Cover data. Land use was expressed as the percentage of each of the six land-use types recognized in the watershed (urban, industrial, mining, cultivated land, forested land, and water bodies). Drainage area, distance from the source, dominant geology, and geo-spatial measures (latitude, longitude, and altitude) were also obtained from this database. Slides, prepared material, and aliquots of the srcinal samples were deposited in the Botany Department of the University of Santiago de Compostela.Light microscope observations on the new species and micrographs were conducted using a Zeiss Axioskop 2 microscope (Zeiss, Jena, Germany) equipped with phase-contrast and with an Axiocam digital camera. SEM observations were made primarily at the Museo delle Scienze us-ing a LEO XVP (Carl Zeiss SMT Ltd., Cambridge, UK) at high vacuum on gold coated prepared material. All of the observations and photographs referred to in the present note were done on epilithon samples. To assess valve dimensions and stria density, a certain number of randomly selected (first encountered) specimens (33) were measured. Measurements stopped when it ap-peared with sufficient confidence that the size range of the population had been adequately docu-mented. Results  Naviculadicta langebertalotii  M. Cantonati & M. Leira sp. nov.  ( Figs.  1– 3)D IAGNOSIS : Valvae plerumque lineari-lanceolatae vel stricte lineari-lanceolatae, marginibus saepe modice concavis, valvae ita saepe panduriformes. Apicibus obtusatis vel cuneatis, non protrac-tis. Longitudo 12 – 26 µm, latitudo 4.5 – 5.5 µm. Raphe recta filiformis, extremis centralibus fere dense sitis inter se. Raphe cum poris centralibus parvis exigue deflexis ad latus valvae opposi-tum ut fissurae terminales. Striae transapicales (longiores arcuatae), 16 – 23 in 10 µm, in media parte et sub apices plerumque subparallelae aliae radiantes. Lineae longitudinales utroque latere arae axialis spectabiles. Area axialis anguste linearis exiguissime transapicaliter et unilaterali-ter expansa in media parte. Aspectus ultramicroscopicus vide Fig urae 2 – 3. Areolae occlusae hymenibus externis, 40 – 45(50) in 10 µm. Areolae area axiali proximae transapicaliter parum elongatae et generaliter distincte crassae (causa linearum longitudinalium). Cingulum ex paucis (2 – 3) copulis constans. Raphe fissuris terminalibus externis uncinatis. Fissuris terminalibus in facie valvae margines non attingentes.  Navicula oregonensis  Hustedt aliquid similis differt pro-prie valvis valde latioribus.D ESCRIPTION : The new species is a naviculoid diatom, not rarely with a slight cymbelloid hint ( Fig.  1, Fig.  2 A). Outline linear-lanceolate to narrowly linear-lanceolate, with a tendency to be narrowly panduriform. Margins accordingly linear to moderately concave. Apices obtuse to cu-neate, not protracted. LM ( Fig.  1 A–T): Length: 12 – 26 µm (average  = 18 µm; N  = 33). Width: 4.5 – 5.5 µm (average  = 5 µm; N  = 33). Raphe branches straight, filiform; central endings only very slightly bent. Striae parallel in the central part, soon becoming moderately radial (the longest ones slightly arched), becoming parallel again towards the apices; 16 – 23 in 10 µm (average  = 19 in 10 µm; N  = 33). Proximal raphe ends relatively close to each other, and only very slightly bent in the same di-rection which is opposite to that one towards which the terminal fissures are curved (compare Fig.  2 A). Faint longitudinal lines visible on both sides of the raphe (e.g., Fig.  1 A–C,J,O) in valves lying flat in the permanent mount (in other cases one line is visible, e.g., Fig.  1 K,N,P). Axial area narrow and straight, slightly widening towards the central area that is just a small eschweizerbart_xxx  74M. Cantonati et al. (sometimes almost non-perceptible) unilateral expansion of the axial area. SEM outside  ( Fig.  2 A–C): Areolae simple, roundish or transapically elongated ( Fig s 2 – 3), closed outside by hymenes ( Fig.  2 C), 40 – 45(50) in 10 µm. Striae continue uninterrupted from the valve face to the valve mantle ( Fig.  2 B, Fig.  3 A). The terminal areolae of the striae clos-est to the axial area are sometimes transapically more elongated and more marked in general ( Fig.  2 A–B and Fig.  3 B, cause of the longitudinal lines seen in LM). The girdle appears to con-sist of 2 – 3 narrow copulae ( Fig.  2 B, Fig.  3 B). Distal raphe fissures are completely on the valve face, and are hooked ( Fig.  2 A,C). SEM inside  ( Fig.  3 A–D): Valve mantle strongly bent off ( Fig.  2 B, Fig.  3 A). Mantle height re-ducing in the central part and somewhat abruptly at the poles ( Fig.  3 A,D). Raphe raised on a median rib (sternum; Fig.  3 A). Proximal raphe endings clearly deflected towards the side where the axial area slightly expands ( Fig.  3 C). Raphe branches end distally in a somewhat elongated small helictoglossa ( Fig.  3 D). Short striae consisting of 2(3) areolae only follow the profile of the apices ( Fig.  3 B,D).S PECIES   COMPARISON : The new species is distinguished by a rather peculiar character combination. Of the established naviculoid genera, it mostly resembles  Adlafia  Lange-Bertalot but striae are not as dense and abruptly convergent towards the valve ends, and there are several minor dif-ferences, e.g. in the outline and exact position of the external terminal raphe fissures etc. The most similar  Navicula  sensu lato species are  Navicula natchikae  J. B. Petersen and  Navicula oregonensis  Hustedt (Hustedt 1961–1966). Both are clearly larger, and have parallel straight mar-gins (opposed to frequently slightly concave in  Naviculadicta langebertalotii ).  N. oregonensis  [L  = 63 µm, B  = 14 µm, Hustedt (1961–1966): much larger than  N. langebertalotii ], interestingly Fig. 1.  LM micrographs of  Naviculadicta langebertalotii sp. nov., type material (Verdugo, Sautomaior). (G,K,R) phase contrast, all the others brightfield. 1500 x. Scale bar, 10 µm. eschweizerbart_xxx  75 Naviculadicta langebertalotii   sp. nov. presents longitudinal lines on both sides of the axial area. Striae are, however, interrupted close to the valve margin by a longitudinal rib (absent in  N. langebertalotii ) developing parallel to the valve margin.  N. natchikae  is now included in the recently described genus  Boreozonacola  Lange-Bertalot, Kulikowskiy & Witkowski (Kulikowskiy et al. 2010) that clearly differs from  Naviculadicta langebertalotii  for several characters, in particular by the shape of the terminal raphe fissures developing on the valve face and mantle, the distinct Voigt fault, and the areolae occluded by hymenes inside (outside in  N. langebertalotii ).H OLOTYPE : Collected by M. C. López Rodríguez on the 22 nd  of September 2006. Deposited in the diatom collection of the Museo delle Scienze (Trento, Italy), Code   cLIM004 DIAT 1891 . I SOTYPES : Diatom collection  Botanischer Garten und Botanisches Museum Berlin-Dahlem, Freie Universität Berlin  (Berlin, Germany), Code B 40 0040732, and ANSP Diatom Herbarium (The Academy of Natural Sciences of Philadelphia, USA), Codes: ANSP GC 14452 (isotype slide), and ANSP GCM 15137 (cleaned material).T YPE   LOCALITY : The type locality (Soutomaior, at the River Verdugo) is a stream stretch located in a narrow valley with steep slopes. The river bed is dominated by hard geological substrata, such as granites and phyllites. No intensive agricultural and important livestock activities are carried Fig. 2.  SEM outside micrographs of  Naviculadicta langebertalotii sp. nov., type material. (A) Valve-face outside view (note the raphe course). (B) Apical part of the frustule (note more marked and/or transapically elongated areolae on both sides of the raphe, and girdle bands. (C) Apical part of the valve (note terminal ending of the raphe, and areolae closed outside). Scale bars, 1 µm. eschweizerbart_xxx
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