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1 This article was downloaded by: [UGR-BTCA Gral Universitaria] On: 02 May 2014, At: 01:34 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Diatom Research Publication details, including instructions for authors and subscription information: Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta) Oscar E. Romero a & Regine Jahn b a Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla-Granada, Spain b Botanic Garden and Botanical Museum Berlin-Dahlem, Freie Universität Berlin, Berlin, Germany Published online: 11 Mar To cite this article: Oscar E. Romero & Regine Jahn (2013) Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta), Diatom Research, 28:2, , DOI: / X To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 Diatom Research, 2013 Vol. 28, No. 2, , Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta) OSCAR E. ROMERO 1 & REGINE JAHN 2 1 Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla-Granada, Spain 2 Botanic Garden and Botanical Museum Berlin-Dahlem, Freie Universität Berlin, Berlin, Germany The nominate varieties of the monoraphid diatoms Cocconeis lineata Ehrenberg and C. euglypta Ehrenberg are typified. Lectotypes of both taxa are preserved at the Ehrenberg Collection, Museum für Naturkunde, Berlin, Germany. The lectotype of C. lineata is a poorly detailed drawing, showing an ovoid valve (or frustule?) with two to three apical lines on each hemivalve. The lectotype of C. euglypta, contained in a mica, shows a unique, broadly elliptical sternum valve with up to five apical striae on each hemivalve, displaying a zigzag pattern. This is roughly consistent with the current concept of C. lineata and C. euglypta and with their usage over the last 160 years. To ensure stabilization of the names and current concepts for these two taxa, culture-based epitypes of C. lineata and C. euglypta are designated. Light and electron microscopy observations, as well as morphometric data from clones for both taxa, are presented and an amended description for each taxon is provided. Keywords: lectotype, epitype, Cocconeis culture, morphometric data Introduction The prolific research on microorganisms accomplished by Christian G. Ehrenberg ( ) included finding and naming diatoms from many different habitats (Jahn 1995). Unlike many of his contemporaries, Ehrenberg did not send out duplicate material to colleagues, hence our understanding of his taxonomic entities must be mainly based on his original materials and his publications (Lazarus & Jahn 1998). In spite of the accurate work he carried out in collecting, depositing, drawing and describing microalgae, the names given by Ehrenberg to new taxa have to be carefully evaluated (Jahn et al. 2005). The study of taxa described by Ehrenberg also concerns the monoraphid diatom genus Cocconeis Ehrenberg. In his early compendium book Infusionsthierchen, Ehrenberg (1838) described Cocconeis in Latin and French, and offered a great deal of information on his understanding of the morphology, habit and habitat of this diatom genus. Because Cocconeis mostly sits like a buckler ( Schild in German) attached by its raphe sternum valve (RSV) on filamentous algae or other substrata, he named it after the insect genus Coccus (scale house or Schildlaus in German). Ehrenberg (1843) first mentioned C. lineata without publishing any diagnosis or drawing. A decade later, based on material collected in Lyon (France), he published the first drawing of C. lineata (Ehrenberg 1849). Based on the morphological similarity between C. lineata and C. placentula Ehrenberg var. placentula, Van Heurck (1885) proposed the combination of C. placentula var. lineata. Cocconeis euglypta was first described by Ehrenberg in Grunow (1884) was the first to propose the combination of C. placentula var. euglypta. Although several comprehensive revisions (Riaux- Gobin & Romero 2003, De Stefano & Romero 2005, De Stefano et al. 2008) and regular research papers (e.g., Romero & Navarro 1999, Suzuki et al. 2001) have studied numerous Cocconeis taxa in the last two decades, the study of type material of Cocconeis remains to be fulfilled, mainly regarding those species and varieties described in the nineteenth century (Jahn et al. 2009, Romero 2011). By providing morphological observations and morphometric data from clones as well as from natural populations, Jahn et al. (2009) typified the nominate varieties of C. pediculus Ehrenberg and C. placentula. The most common approach to the identification of both C. lineata and C. euglypta follows the current concepts available in the literature, without any reference to the type material of these two species; except for Monnier et al. (2007) who compared the drawings of different authors (see also Tables 1 2). In this work, a similar approach is followed as in Jahn et al. (2009). In addition to the study of type material of C. lineata and C. euglypta, kept at the Ehrenberg Collection (Museum für Naturkunde, Berlin, Germany), the morphology of clones of two Cocconeis species were studied. Corresponding author. oromero@ugr.es (Received 4 August 2012; accepted 21 January 2013) 2013 The International Society for Diatom Research

3 Table 1. Comparison of morphometric data and autecology for Cocconeis lineata from the literature and this study. AA TA AA:AT RV striae SV striae Reference (μm) (μm) ratio in 10 μm in 10μm Autecology C. lineata Ehrenberg 28* 14* n. d. n. d. n. d. Dust (1849) C. placentula var. lineata ca. 70 n. d. n. d. ca. 17 n. d. Brackish waters, rare Van Heurck (1885) C. placentula var. lineata Periphyton, common in freshwater, either sec. Hustedt (1930) same as same as same as same as same as occurring as single species or together var. var. var. var. var. with the nominate variety placentula placentula placentula placentula placentula C. placentula var. lineata n. d As the nominate variety: Widespread sec. Patrick & Reimer [up to 22 eurytopous species epiphytic on aquatic (1966) areolae plants and other objects. More commonly per stria] found in circumneutral to alkaline waters (alkaliphil?); apparently salt indifferent but not observed in great numbers in slightly brackish waters C. placentula var. lineata sec. Geitler (1982) n. d. n. d. n. d Stream in Lunz (Austria): cold, stream waters, from the northern calcareous Alps C. placentula var. lineata n. d. Same as Cites Geitler 1958: Cosmopolitan, epiphyte; occurring sec. Krammer & [all varieties] var. small v.: 18 23; commonly and often in masses; Lange-Bertalot (2004) placentula large v.: [3 10 areolae per stria] especially var. eugylpta, var. lineata and var. placentula. They live in standing and running waters, also on non-living objects such as wood and stones C. lineata sec. Kobayasi n. d Unknown et al. (2006) [18 22 [6 12 areolae per stria] areolae per stria] C. lineata sec. Monnier n. d. n. d. n. d. n. d. [5 12 areolae Well differentiated against C. euglypta: et al. (2007) per stria] tolerates lower trophy, saproby and conductivity C. lineata sec. this n. d Creek at Lambi, Eysturoy Island, study Ø 21.2 Ø 11.2 Ø 1.9 Ø 16.5 Faroer Islands, Denmark Epitype-strain D n = 56 n = 56 n = 56 n = Romero & Jahn Notes: AA: apical axis, TA: transapical axis; RV: raphe-sternum valve; SV: sternum valve; n.d.: no data. *Metric data from Fig. 1 8.

4 Table 2. Comparison of morphometric data and autecology for Cocconeis euglypta from the literature and this study. AA TA AA:AT RV striae SV striae Reference (μm) (μm) ratio in 10 μm in10μm Autecology C. euglypta Ehrenberg (1854) C. lineata var. euglypta Grunow in Van Heurck (1880) C. placentula var. euglypta Grunow (1884) 28* 16* n. d. n. d. 14* River in Florida 31 33* 20* n. d. n. d. n. d. Not mentioned in text but as C. lineata var. euglypta in two figures (Pl. 30, figs 33 34) n. d. n. d One frustule observed, only SV striae recognizable C. placentula var. euglypta Periphyton, common in freshwater, either sec. Hustedt (1930) same as same as same as same as occurring as single species or together var. var. var. var. with the nominate variety placentula placentula placentula placentula C. placentula var. euglypta greater than As the nominate variety: Widespread sec. Patrick & Reimer (1966) lineata [2 5 areolae per stria] eurytopous species, epiphytic on aquatic plants and other substrata. More commonly found in circumneutral to alkaline waters (alkaliphil?); apparently salt indifferent but not observed in great numbers in slightly brackish waters C. euglypta sec. Germain n. d n. d. (1981) C. placentula var. euglypta n. d. same as Cosmopolitan, epiphyte; occurring sec. Krammer & [all varieties] var. [3 5 areolae commonly and often in masses; Lange-Bertalot (2004) placentula per stria] especially var. eugylpta var. lineata and var. placentula. In standing and running waters, also on non-living substrata such as wood and stones C. euglypta sec. Monnier n. d. n. d. n. d. n. d. [2 5 areolae Well differentiated against C. lineata: et al. (2007) per stria] tolerates more trophy, saproby and higher conductivity C. euglypta sec. this n.d Periphytic in shallow brackish study Ø 18.3 Ø 11.2 Ø 1.7 Ø 21.8 waters near Wismar, Baltic Sea Epitype-strain WiCoc02 n = 31 n = 31 n = 31 n = 31 Notes: AA: apical axis, TA: transapical axis; RV: raphe sternum valve; SV: sternum valve; n.d.: no data. *Metric data measured from Fig. 9. Typification of two taxa of Cocconeis Ehrenberg 177

5 178 Romero & Jahn Materials and methods The following material from the Ehrenberg Collection at the Museum für Naturkunde, Berlin, Germany was investigated: Cocconeis lineata Ehrenberg (1849). Ehrenberg s materials and drawings from Lyon (Mica EC , Zbl. 2177) and the Genua materials (Mica EC , Zbl. 2176), which contain eolian dust ( Atmosphärische Sphärilen in German). Cocconeis euglypta Ehrenberg (1854). Ehrenberg s material from Florida, Salakchopko River (EC ). In addition to the type material, new material was collected and unialgal Cocconeis strains were established. This material is deposited at the Botanischer Garten und Botanisches Museum Berlin Dahlem (B): Cocconeis lineata. Strain D17_011, voucher B , from Creek at Lambi, Eysturoy Island, Faroe Islands, Denmark, collected and isolated by J. Bansemer, 8 February Cocconeis euglypta. Strain WiCoc02, voucher B , from Wismar, Baltic Sea, collected by R. Jahn, 4 August 2012 and isolated by O. Skibbe. For comparison, the epitype strain D36_012 C. placentula var. placentula was used (see Jahn et al. 2009). Water samples were observed under a stereomicroscope and diatoms were picked out using capillary glass pipettes. Cells were then transferred to 5-cm diameter plastic Petri dishes containing culture medium (WC, Chu, AlgaGrow) of adequate salinity and ph ( ). In order to separate cells and remove attached particles, this treatment was repeated several times, until microscopic inspection confirmed that pure cultures had been established. Cultures were kept at an ambient temperature of C and were illuminated 12:12 h with a 39W T5 fluorescent tube (OSRAM Lumilux Daylight) from a distance of 1 m. The terminology recommended in Anonymous (1975), Ross et al. (1979), Holmes et al. (1982) and Round et al. (1990) was used for the description of frustule features. The sternum and raphe sternum valves are identified as SV and RSV, respectively (Romero & Navarro 1999, Romero 2011). Stria density was counted at the center of the valve face and, if the striae were markedly radiate, also at the margin opposite the center of the valve. In the species description, AA is used for the apical axis, TA for the transapical axis. Results Cocconeis lineata Ehrenberg (Figs 1 8, Tables 1, 3) Protologue. Ehrenberg 1849, Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin 1847, p. 301, pl. 5, part 2, fig. 44. Homotypic synonym. Cocconeis placentula var. lineata (Ehrenberg) Van Heurck (1885). Lectotype (designated here). Figure numbered 37 (in red) C. lineata on Ehrenberg s drawing sheet 2177; here reproduced in Fig. 1. Type locality. Orcan-Staub von Lyon am 17 Oktober 1846 [=eolian dust sample collected in Lyon, France, 17 October 1846]. Epitype (designated here). Slide B , from strain 17_011 (Faroe Islands) (Fig. 2). Epitype locality. Creek at Lambi, Eysturoy Island, Faroe Islands, Denmark, N, 6.71 E, altitude 40 m above sea level. Amended description of Cocconeis lineata Elliptical valves (AA: μm; TA: μm). The SV is externally slightly convex toward the narrow, linear/linear lanceolate sternum, separated from the valve apices by one areola (Figs 3 4). Up to 10 apical striae on each hemivalve are counted. Striae are uniseriate, (7)10 15 in 10 μm, parallel and straight in the valve center, although radiate and curved towards the apices. Areolae, 16 24(26) in 10 μm, are externally dash-shaped (Fig. 3), whereas the internal foramen is ovoid. The valvocopula, open at one end, lacks fimbriae (Fig. 7). The RSV is externally concave and bears a filiform raphe, bordered by a linear narrow sternum with an elliptical or orbicular central area (Fig. 5), proximal and distal raphe ends are coaxial (Fig. 6). RSV striae are uniseriate, parallel and straight in the valve center, radiate towards the valve ends (Figs 2, 5, 8), and range between 20 and 28 in 10 μm. Close to the margin, the striation is interrupted by a submarginal hyaline area, which leaves between one and three areolae separated from the rest (Figs 6, 8). The areola foramen is circular or ovoid on both valve sides (Figs 5 6, 8). The valvocopula, open at one end, is devoid of fimbriae (Fig. 8). Comments Cocconeis lineata is first cited in Ehrenberg (1843: 369), although only its name and occurrence are cited (Atotonilco (Zbl. 2066), Puente de Dios (Zbl. 2065), Vera-Cruz, Mexico (Zbl. 2063)); a figure and diagnosis are missing. According to the International Code of Botanical Nomenclature (McNeill et al. 2006), it is therefore a nomen nudum. The most commonly cited figure appeared years later in the Mikrogeologie (Ehrenberg 1854, pl. 39, part 3, fig. 11), although no description was provided. The Mikrogeologie is, however, a compendium of works published by Ehrenberg years earlier. The first two published drawings under the name Cocconeis lineata are seen in his work

6 Typification of two taxa of Cocconeis Ehrenberg 179 Figs 1 8. Cocconeis lineata, drawing (Fig. 1), LM (Fig. 2), SEM external (Figs 3, 5) and internal (Figs 4, 6 8) views. Fig. 1. Lectotype; Original illustration from Ehrenberg Collection (BHUPM), part of Ehrenberg s drawing sheet Nr Fig. 2. Sternum (left) and raphe sternum (right) valves from the epitype slide B Figs 2 8. Monoclonal culture, strain D17_011. Fig. 3. Sternum valve. Fig. 4. Sternum valve. Fig. 5. Raphe sternum valve. Fig. 6. Raphe sternum valve. Fig. 7. Sternum valve with valvocopula. Fig. 8. Raphe sternum valve, with valvocopula. Scale bars = 10 μm (Fig. 2), 5 μm (Figs 3 6), 2 μm (Figs 7 8). on wind-transported material collected in near-shore locations of the Mediterranean Sea and the Atlantic Ocean in the 1840s (Ehrenberg 1849). On the mica containing the eolian dust collected in 1846 in Le Verpillière between Lyon and Grenoble, France, only C. atmosphaerica Ehrenberg has been found ( Diploneis atmosphaerica (Ehrenberg) Jahn & Kusber (Jahn & Kusber 2004)). The mica containing the material Ehrenberg received from Genua (Italy) shows, however, no valves of Cocconeis. After checking Ehrenberg s drawing sheets corresponding to the Lyon (Zbl. 2177) and Genua materials (Zbl. 2176), drawings of C. lineata were found that agree with the figures of his 1849 publication. Because Ehrenberg s drawing of the Lyon material has also the name Cocconeis lineata written below the only valve drawn, this drawing was selected as the lectotype of C. lineata (Fig. 1). In his revision of Ehrenberg s type material, Tuji (2009) examined drawings and mica preparation assigned to C. lineata. Unfortunately, Tuji s lectotypification of C. lineata is incorrect. Cocconeis lineata, first mentioned in Ehrenberg (1843), has to be considered a nomen nudum (see above). The next date when Ehrenberg published a figure with this name was from the Lyon and Genua material (Ehrenberg 1849); even if he did not publish a diagnosis, this is considered a valid name (before 1908; see also Jahn & Kusber 2009). The figure and materials to which Tuji (2009) referred were published later and are, therefore, superseded by our lectotypification. According to our own assessment, the only valve of C. lineata drawn by Ehrenberg measures 29.4 μm (AA) by 16.3 μm (TA). The AA:TA ratio for the unique Ehrenberg s C. lineata valve (1.8) falls within the range measured for the Faroe clone ( ) (Table 3) and matches its average very well (1.8, n = 56). Unfortunately, no transapical striae are recognizable (Fig. 1). The first published drawing of C. lineata might represent a frustule. Although this is speculative and difficult to state in view of the poor detail of Ehrenberg s drawing (Fig. 1), the presence of apical lines on both hemivalves, a central area and a submarginal line can be interpreted as features typical of both valves of C. lineata (Figs 2 8). As shown by valves from the Faroe Islands, the occurrence of

7 180 Romero & Jahn a central area is common to the RSV (Figs 5 6) rather than to the SV (Figs 3 4), whereas the apical lines on both sides of the raphe sternum might represent the apical areolae of the SV. The submarginal line, as drawn by Ehrenberg surrounding the valve almost entirely (Fig. 1), may represent submarginal thickening of the RSV (Figs 6, 8). Because of this, it is speculated that his drawing might represent, instead of only one detached valve, the whole frustule. Cocconeis euglypta Ehrenberg (Figs 9 18, Tables 2 3) Protologue. Ehrenberg 1854, Mikrogeologie, Atlas, p. 8, pl. 34, part 6-A, fig. 2 (no description presented). Homotypic synonyms. Cocconeis lineata var. euglypta (Ehrenberg) Grunow in Van Heurck 1880, pl. 30, figs 33 34; C. rouxii var. euglypta (Ehrenberg) Héribaud ; C. placentula var. euglypta (Ehrenberg) Cleve Lectotype (designated here). here reproduced in Fig. 9. Type locality. BHUPM EC d bl; Salakchopko River, Florida, USA. Epitype (designated here). Strain WiCoc02, voucher B , see Figs Epitype locality. Epiphytic on the red alga Ceramium rubrum in shallow coastal waters, Baltic Sea, pier Bad Wendorf, near Wismar, Germany; N, E, altitude 0 2 m above sea level. Amended description of Cocconeis euglypta Elliptical valves (AA: μm; TA: μm). The SV bears about five apical striae with a zigzag longitudinal pattern on each hemivalve (Figs 9 10), concave toward the narrow, linear sternum (Fig. 12). Striae ( in 10 μm) are uniseriate, mostly radiate, more curved towards the valve apices (Figs 9, 12), and consist of alveoli with roundish internal foramina (Figs 13 15). The valvocopula, open at one end, bears very short digitiform fimbriae (Fig. 15). The concave RSV has a rectilinear raphe, which ends on the internal side of the submarginal hyaline area (Figs 11, 16). A small elliptical central area is observed (Figs 16 17). Striae are uniseriate, in 10 μm, parallel in the middle, radiate toward the valve apices, slightly curved (Figs 11, 16), interrupted by a submarginal hyaline area (Figs 16 18). One or two marginal areolae are slightly separated from those of the valve face by a submarginal hyaline area. A small helictoglossa reaches the internal border of the submarginal hyaline area (Fig. 18). Valvocopula opened with short, slightly laterally expanded fimbriae (Figs 17 18). Comments Ehrenberg (1853) first mentioned the name C. euglypta in a list of species from Florida. In his Mikrogeologie, he (1854) again provided this name, a picture and some information on its occurrence, albeit that a complete diagnosis is missing. According to the International Code of Botanical Nomenclature (McNeill et al. 2006), if a name was published with a picture before 1908 this is valid and not considered a nomen nudum (see also Jahn & Kusber 2009). The mica preserving the type material of C. euglypta contains only one elliptical SV, with up to six apical striae depicting a zigzag apical pattern (Fig. 9). No RSV is present. For this SV, the measured AA is close to 28 μm, while the TA measures 16 μm; striae are around 14 in 10 μm. The stria density for this unique valve is lower than the values obtained for the epitype strain WiCoc02 (Table 3), but it shares the zigzag pattern along the apical axis as well the elliptical to broadly elliptical valve outline (Figs 9 10). As for many other diatom taxa originally described by Ehrenberg (e.g., Jahn & Kusber 2004, Jahn et al. 2009), changes in the systematic status of C. euglypta have been proposed over time. These taxonomic changes are possibly related to the morphological similarity between C. euglypta and C. lineata, as well as to the incomplete characterization of both diatoms when initially described. Grunow proposed C. euglypta as a variety of C. lineata (Grunow in Van Heurck 1880), while Héribaud ( ) introduced C. rouxii var. euglypta. The first appearance of C. euglypta as a variety of C. placentula is that of Grunow (1884). As for C. lineata, the combination C. placentula var. euglypta became common in the following decades (e.g., Cleve 1895, Hustedt 1930, Germain 1981, Suzuki & Nagumo 2002), without further discussion of the main morphological features of their valve relating C. lineata and C. euglypta to C. placentula var. placentula. For example, Hustedt (1930) pictured C. euglypta without explicitly citing or describing C. placentula var. placentula. Some later authors subsumed both C. lineata and C. euglypta as varieties of C. placentula (e.g., Germain 1981, Holmes et al. 1982). Subsuming several varieties, however, tends to blur understanding of the nominate variety, here var. placentula, which presents the original concept of the species (Jahn et al. 2009). Only in recent decades has the nominate variety been picked up again and a few pictures are presented which are supposed to represent C. placentula var. placentula (e.g., Patrick & Reimer 1966, Krammer & Lange-Bertalot 2004, Kobayasi et al. 2006, Jahn et al. 2009). Discussion The occurrence of valves with transitional morphology between C. lineata and C. euglypta has been argued as an impediment for distinguishing both as separate taxa (e.g., Geitler 1927, 1932, Foged 1977, Germain 1981). Several

8 Typification of two taxa of Cocconeis Ehrenberg 181 Figs Cocconeis euglypta, LM (Figs 9 11), SEM external (Figs 12 13, 16) and internal (Figs 14 15, 17, 18) views. Fig. 9. Lectotype; Original material from Ehrenberg Collection mica preparation BHUPM EC d bl. Figs Monoclonal culture, strain WiCoc02; epitype slide B Fig. 10. Sternum valve. Fig. 11. Raphe sternum valve. Fig. 12. Sternum valve. Fig. 13. Sternum valve showing detail of areolae and valve margin. Fig. 14. Entire sternum valve with valvocopula. Fig. 15. Sternum valve showing short fimbriae (arrows) and open end of valvocopula (asterisk). Fig. 16. Raphe sternum valve. Fig. 17. Entire raphe sternum valve showing open end of valvocopula. Fig. 18. Raphe sternum valve showing detail of raphe, helictoglossa, areolae, valvocopula and fimbriae (arrows). Scale bars = 10 μm (Figs 9 12, 14, 16 17), 2 μm (Figs 13, 15), 1 μm (Fig. 18).

9 182 Romero & Jahn Fig. 19. Relation between the number of striae measured in the central valve part at margin and the AA:TA ratio of sternum valve of C. lineata (red dots) and C. euglypta (gray crosses) from the two epitype strains. The regression represent linear fittings for each epitype strain. studies have discussed the difficulties in distinguishing between C. euglypta and C. lineata and in distinguishing them from other morphologically related varieties of C. placentula. For example, Patrick & Reimer (1966) proposed that the ratio between the apical and transapical axes (AA:TA in Fig. 19) varies more in C. euglypta than in C. lineata. Our observations do not support this statement (Table 3). However, when the number of SV striae is plotted against the AA:TA ratio (Fig. 19), differences in morphometry between both taxa are seen. In spite of some values overlapping and the similarity in the AA:TA ratio of both taxa (Table 3), the density of the transapical striae seems a reliable character. Although the valves C. lineata and C. euglypta show similarities in their overall morphology, the morphometry of their valves supports the separation of both taxa (Fig. 19, Table 3). Monnier et al. (2007) argue that a certain degree of confusion in the basic concept of C. lineata and C. euglypta is due to the fact that many diatom floras present micrographs without the addition of the pertaining description and morphometric data (Tables 1 2). The presence of up to six apical striae on each hemivalve is an easily recognizable structural feature of the SV of C. euglypta (Figs 9 10, Table 2), whereas six to ten apical striae seem to be the rule in SV of C. lineata (Figs 2 4, Table 1). It is speculated that this confusion partially relates to different ranges of apical striae as reported by different authors. The density of apical striae in our strain of C. euglypta matches the range reported in Van Heurck (1885), although it is slightly lower than other reported values (up to six, Patrick & Reimer 1966, Dexiang et al. 1985, Suzuki & Nagumo 2002), and falls within the range given by Krammer & Lange-Bertalot (1991, three to ten). Regardless of the number of apical striae, the typical zigzag apical areolar arrangement can be recognized as a constant feature among different descriptions (Dexiang et al. 1985, Krammer & Lange-Bertalot 1991). Because of the lack of important morphological differences between the RSV of C. lineata (Figs 2, 5 6) and C. euglypta (Figs 11, 16 17), respective descriptions have hardly considered its characteristics (Tables 1 2). The similar overall morphology of the RSV of C. lineata and C. euglypta and the occurrence of a submarginal hyaline ring (Figs 5 6, 16 17) morphologically both relate to C. placentula var. placentula (see Figs 28, 30, and in Jahn et al. 2009). Our research on Cocconeis followed a purely morphological approach. The morphological and morphometric variability presented in our study is based on observations of valves grown under controlled laboratory cultures of a single clone. Monnier et al. (2007) argued that the overall aspects of SV of C. lineata and C. euglypta strongly vary under different ecological conditions, and concluded that both species respond differently under different nutrient supply. Studying populations of Cocconeis collected in the Rhine Meuse basin (northwest France) between 2000 and 2005, Monnier et al. concluded that C. lineata is typical of oligotrophic waters, whereas C. euglypta is ubiquitous, although more abundant in mesotrophic waters and Table 3. Comparison of morphometric data for the epitype strains of C. placentula var. placentula (strain D36 012) (Jahn et al. 2009), C. lineata (strain D17 011) and C. euglypta (strain WiCoc02) (this study). AA Avg ± SD Avg ± SD AA:TA Striae Taxon n (μm) (μm) TA (μm) (μm) ratio Avg ± SD (in 10 μm) Avg ± SD C. placentula epitype strain D C. lineata epitype strain D C euglypta epitype strain WiCoc ± ± ± ± ± ± ± ± ± ± ± 1.02 Notes: n: numbers of specimens studied; AA: apical axis; TA: transapical axis; Avg: average; SD:, standard deviation.

10 supports different pollution levels (Monnier et al. 2007). Together with the morphological observations presented here, the consideration of ecological conditions seems to be equally helpful when trying to distinguish between C. lineata and C. euglypta. The habitats of the epitypes are either oligotrophic (C. lineata) or high-conductivity waters (C. euglypta). Concerning the type locality of the epitypes, it would have been preferable to designate strains from the type localities. For C. lineata, it is dust at Lyon and therefore could be any place; for C. euglypta, it is a river in Florida (USA). Because the current concept is European, it was decided to use available European cultures, which have similar morphology and ecology. Nowadays, it is becoming important to designate epitypes explanatory types which support the current concepts and offer micro-morphological as well as molecular data in order to establish reference libraries with DNA barcodes for molecular identification (Zimmermann et al. 2011, Pawlowski et al. 2012). Whether C. lineata and C. euglypta should keep the rank of a species is still a matter of debate. In view of the morphological differences among C. lineata and C. euglypta (Table 3), and C. placentula var. placentula as well as other Cocconeis species with a Cocconeis placentuloid-like morphology (O. Romero & M. De Stefano, unpubl.), we propose to keep both taxa at the species rank. Ongoing molecular research on several clones collected from European and East Asian localities will hopefully allow us to answer this question and solve this taxonomic uncertainty. Acknowledgements We gratefully acknowledge the help of Jana Bansemer with collecting and culturing diatoms, of Monika Lüchow at the SEM (both at the Botanic Garden and Botanical Museum Berlin), and of Oliver Skibbe (Berlin, Germany) for isolating and culturing. The German Federal Ministry of Education and Research (BMBF) (grants 01 LC 0026 & 01 LI 1001 A) supported the work in the Ehrenberg Collection as part of the AlgaTerra project as well as the data mobilization for GBIF. OER was partially supported by the Spanish Council of Scientific Research and by the Synthesys Project (DE-TAF-1136), which is funded by the European Community Research Infrastructure Action under the FP6 Structuring the European Research Area Programme. References Anonymous Proposal for standardization of diatom terminology and diagnoses. Beihefte zur Nova Hedwigia 53: Cleve P.T Synopsis of the naviculoid diatoms. Kongliga Svenska Vetenskaps-Akademiens Handlingar 27: De Stefano M. & Romero O.E A survey of alveolate species of the diatom genus Cocconeis (Ehr.) with remarks on the new section Alveolatae. Bibliotheca Diatomologica 52: De Stefano M., Romero O.E. & Totti C A comparative study of Cocconeis scutellum Ehrenberg and its varieties (Bacillariophyta). Botanica Marina 51: Typification of two taxa of Cocconeis Ehrenberg 183 Dexiang J., Zhaodi C., Junmin L. & Shicheng L The marine benthic diatoms in China. Vol. I. China Ocean Press, Beijing. 313 pp. Ehrenberg C.G Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben der Natur. 548 pp. Ehrenberg C.G Verbreitung und Einfluss des mikroskopischen Lebens in Süd- und Nord-Amerika. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin 1841: Ehrenberg C.G Passatstaub und Blutregen. Ein grosses organisches unsichtbares Wirken und Leben in der Atmosphäre. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin 1847: Ehrenberg C.G Das jetzige mikroskopische Leben als Flusstrübung und Humusland in Florida. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königlich- Preussischen Akademie der Wissenschaften zu Berlin 1853: Ehrenberg C.G Mikrogeologie. Das Erden und Felsen schaffende Wirken des unsichtbar kleinen selbstständigen Lebens auf der Erde. Atlas. T Leopold Voss, Lepzig. 374 pp. Foged N Freshwater diatoms in Ireland. Bibliotheca Phycologica 34: Geitler L Somatische Teilung, Reduktionsteilung, Copulation und Parthenogenese bei Cocconeis placentula. Archiv für Protistenkunde 59: Geitler L Der Formwechsel der pennaten Diatomeen (Kieselalgen). Archiv für Protistenkunde 78: Germain H Flores des Diatomophycées. Eaux douces et saumâtres du massif Armoricain et des contrés voisines d Europe Occidentale. Socitété Nouvelle Édition Boubée, Paris. 444 pp. Grunow A Die Diatomeen von Franz Josefs-Land. Denkschriften der Kaiserliche Akademie der Wissenschaft in Wien 48: Héribaud F.J Les diatomées d Auvergne. Librairie des Sciences Naturelles, Paris. pp , pl. 1 6 (1893); deuxieme mémoire, pp , pl (1903). Holmes R.W., Crawford R.M. & Round F.E Variability in the structure of the genus Cocconeis Ehr. (Bacillariophyta) with special reference to the cingulum. Phycologia 21: Hustedt F Bacillariophyta (Diatomeae). In: Die Süsswasserflora von Mittleuropa (Ed. by A. Pascher). G. Fischer, Jena. 466 pp. Jahn R C.G. Ehrenberg s concept of the diatoms. Archiv für Protistenkunde 146: Jahn R. & Kusber W.-H Algae of the Ehrenberg Collection 1. Typification of 32 names of diatom taxa described by C. G. Ehrenberg. Willdenowia 34: Jahn R. & Kusber W.-H A key to diatom nomenclature. Diatom Research 24: Jahn R., Sterrenburg F.A.S. & Kusber W.-H Typification and taxonomy of Gyrosigma fasciola (Ehrenb.) J.W. Griffith et Henfrey. Diatom Research 20: Jahn R., Kusber W.-H. & Romero O.E Cocconeis pediculus Ehrenberg and C. placentula Ehrenberg var. placentula (Bacillariophyta): Typification and taxonomy. Fottea 9:

11 184 Romero & Jahn Kobayasi H., Idei M., Mayama S., Nagumo T. & Osada K H. Kobayasi s atlas of Japanese diatoms based on electron microscopy. Uchida Rokakuho Publishing Co. Ltd., Tokyo. Krammer K. & Lange-Bertalot H Bacillariophyceae 4. Teil: Achnanthaceae. Kritische Ergänzungen zu Navicula (Lineolatae) und Gomphonema Gesamtliteraturverzeichnis Teil 1 4. In: Süsswasserflora von Mitteleuropa (Ed. by H. Ettl, G. Gärtner, J. Gerloff, H. Heynig & D. Mollenhauer), Vol. 2/4. Gustav Fisher Verlag, Stuttgart. 437 pp. Krammer K. & Lange-Bertalot H Bacillariophyceae 4. Teil: Achnanthaceae. Kritische Ergänzungen zu Navicula (Lineolatae) und Gomphonema Gesamtliteraturverzeichnis Teil 1 4. In: Süsswasserflora von Mitteleuropa (Ed. by H. Ettl, G. Gärtner, J. Gerloff, H. Heynig & D. Mollenhauer), Vol. 2/4, second edition. Spektrum Akademischer Verlag, Heidelberg. 468 pp. Lazarus D. & Jahn R Using the Ehrenberg collection. Diatom Research 13: McNeill J., Barrie F.R., Burdet H.M., Demoulin V., Hawksworth D.L., Marhold K., Nicolson D.H., Prado J., Silva P.C., Skog J.E. & Wiersema J.H International code of botanical nomenclature. Regnum Vegetabile. Koeltz Scientific Books, Koenigstein. 568 pp. Monnier O., Rimet F., Bey M., Chavaux R. & Ector L Sur l identité de Cocconeis euglypta Ehrenberg 1854 et C. lineata Ehrenberg 1843 Une approche par les sources historiques. Diatomania 11: Patrick R. & Reimer C.W The diatoms of the United States, exclusive of Alaska and Hawaii. Volume 1. Fragilariaceae, Eunotiaceae, Achnanthaceae, Naviculaceae. Monographs 13. Academy of Natural Sciences, Philadelphia. 688 pp. Pawlowski J., Audic S., Adl S., Bass D., Belbahri L. et al CBOL protist working group: Barcoding eukaryotic richness beyond the animal, plant, and fungal kingdoms. PLoS Biol 10(11): e doi: /journal.pbio Riaux-Gobin C. & Romero O.E Marine Cocconeis Ehrenberg (Bacillariophyceae) species, and related taxa, from Kerguelen s Land (Austral Ocean, Indian Sector). Bibliotheca Diatomologica 47: Romero O.E Morphological study of the genus Cocconeis Ehrenberg (Bacillariophyceae) collected during the Belgian Antarctic Expedition. Botanica Marina 54: Romero O.E. & Navarro J.N Two marine species of Cocconeis Ehrenberg (Bacillariophyceae): C. pseudomarginata Gregory and C. caribensis sp. nov. Botanica Marina 42: Ross R., Cox E.J., Karayeva N.I., Mann D.G., Paddock T.B.B., Simonsen R. & Sims P.A An amended terminology for the siliceous components of the diatom cell. Beihefte zur Nova Hedwigia 64: Round F.E., Crawford R.M. & Mann D.G The diatoms. Biology and morphology of the genera. Cambridge University Press, Cambridge. 747 pp. Suzuki H. & Nagumo T Morphology of freshwater diatom Cocconeis placentula Ehrenberg var. euglypta (Ehrenberg) Grunow. Bulletin of Nippon Dental University, Tokyo 31: (In Japanese with English summary). Suzuki H., Nagumo T. & Tanaka J A new marine diatom, Cocconeis shikinenesis sp. nov. (Bacillariophyceae) from Japan. Phycological Research 49: Tuji A Examination of type material and typification of seven diatoms described by C.G. Ehrenberg. In: Joint Haeckel and Ehrenberg project: Re-examination of the Haeckel and Ehrenberg microfossil collections as a historical and scientific legacy (Ed. by Y. Tanimura & Y. Aita), pp National Museum of Nature and Science Monographs No. 40. Van Heurck H Synopsis des diatomées de Belgique. Atlas. Ducaju & Cie., Anvers. 120 pp. Van Heurck H Synopsis des diatomées de Belgique. Martin Brouwers & Co., Anvers. 235 pp. Zimmermann J., Jahn R. & Gemeinholzer B Barcoding diatoms: evaluation of the V4 subregion on the 18S rrna gene, including new primers and protocols. Organisms Diversity & Evolution 11: