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Typification of Cocconeis lineata and Cocconeiseuglypta (Bacillariophyta)Oscar E. Romero a & Regine Jahn ba Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla-Granada, Spainb Botanic Garden and Botanical Museum Berlin-Dahlem, Freie Universität Berlin, Berlin,GermanyVersion of record first published: 11 Mar 2013.

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Diatom Research, 2013http://dx.doi.org/10.1080/0269249X.2013.770801

Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta)

OSCAR E. ROMERO1∗ & REGINE JAHN2

1Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla-Granada, Spain2Botanic 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 ofboth taxa are preserved at the Ehrenberg Collection, Museum für Naturkunde, Berlin, Germany. The lectotype of C. lineata is a poorlydetailed 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 zigzagpattern. 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 aredesignated. Light and electron microscopy observations, as well as morphometric data from clones for both taxa, are presented and anamended description for each taxon is provided.

Keywords: lectotype, epitype, Cocconeis culture, morphometric data

IntroductionThe prolific research on microorganisms accomplishedby Christian G. Ehrenberg (1795–1876) included find-ing and naming diatoms from many different habitats(Jahn 1995). Unlike many of his contemporaries, Ehren-berg did not send out duplicate material to colleagues,hence our understanding of his taxonomic entities mustbe mainly based on his original materials and his publi-cations (Lazarus & Jahn 1998). In spite of the accuratework he carried out in collecting, depositing, drawingand describing microalgae, the names given by Ehrenbergto new taxa have to be carefully evaluated (Jahn et al.2005). The study of taxa described by Ehrenberg also con-cerns the monoraphid diatom genus Cocconeis Ehrenberg.In his early compendium book Infusionsthierchen, Ehren-berg (1838) described Cocconeis in Latin and French, andoffered a great deal of information on his understandingof the morphology, habit and habitat of this diatom genus.Because Cocconeis mostly sits like a buckler (‘Schild’ inGerman) attached by its raphe–sternum valve (RSV) onfilamentous algae or other substrata, he named it afterthe insect genus Coccus (scale house or ‘Schildlaus’ inGerman).

Ehrenberg (1843) first mentioned C. lineata withoutpublishing any diagnosis or drawing. A decade later, basedon material collected in Lyon (France), he published the firstdrawing of C. lineata (Ehrenberg 1849). Based on the mor-phological similarity between C. lineata and C. placentula

∗Corresponding author. E-mail: oromero@ugr.es

(Received 4 August 2012; accepted 21 January 2013)

Ehrenberg var. placentula, Van Heurck (1885) proposed thecombination of C. placentula var. lineata. Cocconeis eug-lypta was first described by Ehrenberg in 1854. Grunow(1884) was the first to propose the combination of C. pla-centula var. euglypta.

Although several comprehensive revisions (Riaux-Gobin & Romero 2003, De Stefano & Romero 2005, DeStefano et al. 2008) and regular research papers (e.g.,Romero & Navarro 1999, Suzuki et al. 2001) have stud-ied numerous Cocconeis taxa in the last two decades, thestudy of type material of Cocconeis remains to be fulfilled,mainly regarding those species and varieties described inthe nineteenth century (Jahn et al. 2009, Romero 2011). Byproviding morphological observations and morphometricdata from clones as well as from natural populations, Jahnet al. (2009) typified the nominate varieties of C. pediculusEhrenberg and C. placentula.

The most common approach to the identification of bothC. lineata and C. euglypta follows the current conceptsavailable in the literature, without any reference to the typematerial of these two species; except for Monnier et al.(2007) who compared the drawings of different authors (seealso Tables 1–2). In this work, a similar approach is fol-lowed as in Jahn et al. (2009). In addition to the study of typematerial of C. lineata and C. euglypta, kept at the EhrenbergCollection (Museum für Naturkunde, Berlin, Germany),the morphology of clones of two Cocconeis species werestudied.

© 2013 The International Society for Diatom Research

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Table 1. Comparison of morphometric data and autecology for Cocconeis lineata from the literature and this study.

AA TA AA:AT RV striae SV striaeReference (μm) (μm) ratio in 10 μm in 10 μm Autecology

C. lineata Ehrenberg(1849)

28* 14* n. d. n. d. n. d. Dust

C. placentula var. lineataVan Heurck (1885)

ca. 70 n. d. n. d. ca. 17 n. d. Brackish waters, rare

C. placentula var. lineata 11–70 8–40 0.75 23 25 Periphyton, common in freshwater, eithersec. 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 varietyplacentula placentula placentula placentula placentula

C. placentula var. lineata 10–70 8–40 n. d. 19–23 19–20 As the nominate variety: Widespreadsec. 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 inslightly brackish waters

C. placentula var. lineatasec. Geitler (1982)

16–83 n. d. n. d. n. d. 16–23 Stream in Lunz (Austria): cold, streamwaters, from the northern calcareousAlps

C. placentula var. lineata 10–80 8–40 n. d. Same as Cites Geitler 1958: Cosmopolitan, epiphyte; occurringsec. Krammer & [all varieties] var. small v.: 18–23; commonly and often in masses;Lange-Bertalot (2004) placentula large v.: 16–18

[3–10 areolaeper stria]

especially var. eugylpta, var. lineata andvar. placentula. They live in standingand running waters, also on non-livingobjects such as wood and stones

C. lineata sec. Kobayasi 20–80 8–40 n. d. 16–23 14–18 Unknownet 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 andconductivity

C. lineata sec. this 18.6–22.7 6.4–13.1 1.6–2.4 n. d. 12–20 Creek at Lambi, Eysturoy Island,study Ø 21.2 Ø 11.2 Ø 1.9 Ø 16.5 Faroer Islands, DenmarkEpitype-strainD17−011

n = 56 n = 56 n = 56 n = 56

Notes: AA: apical axis, TA: transapical axis; RV: raphe-sternum valve; SV: sternum valve; n.d.: no data.*Metric data from Fig. 1–8.

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Typificationoftw

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Table 2. Comparison of morphometric data and autecology for Cocconeis euglypta from the literature and this study.

AA TA AA:AT RV striae SV striaeReference (μm) (μm) ratio in 10 μm in 10 μm Autecology

C. euglypta Ehrenberg(1854)

28* 16* n. d. n. d. 14* River in Florida

C. lineata var. euglyptaGrunow in Van Heurck(1880)

31–33* 20* n. d. n. d. n. d. Not mentioned in text but as C. lineatavar. euglypta in two figures (Pl. 30, figs33–34)

C. placentula var. euglyptaGrunow (1884)

19 10 n. d. n. d. 20–22 One frustule observed, only SV striaerecognizable

C. placentula var. euglypta 11–70 8–40 0.75 23 19 Periphyton, common in freshwater, eithersec. Hustedt (1930) same as same as same as same as occurring as single species or together

var. var. var. var. with the nominate varietyplacentula placentula placentula placentula

C. placentula var. euglypta 10–50 8–30 greater than 19–23 19–20 As the nominate variety: Widespreadsec. Patrick & Reimer(1966)

lineata [2–5 areolaeper stria]

eurytopous species, epiphytic onaquatic plants and other substrata. Morecommonly found in circumneutral toalkaline waters (alkaliphil?); apparentlysalt “indifferent” but not observed ingreat numbers in slightly brackish waters

C. euglypta sec. Germain(1981)

11–50 8–30 n. d. 17–24 n. d.

C. placentula var. euglypta 10–46 8–40 n. d. same as 19–20 Cosmopolitan, epiphyte; occurringsec. Krammer & [all varieties] var. [3–5 areolae

per stria]commonly and often in masses;

Lange-Bertalot (2004) placentula especially var. eugylpta var. lineata andvar. placentula. In standing and runningwaters, also on non-living substrata suchas wood and stones

C. euglypta sec. Monnieret al. (2007)

n. d. n. d. n. d. n. d. [2–5 areolae Well differentiated against C. lineata:tolerates more trophy, saproby andhigher conductivity

per stria]

C. euglypta sec. this 15.9–29.5 9.8–17.6 1.5–1.8 n.d. 20–24 Periphytic in shallow brackishstudy Ø 18.3 Ø 11.2 Ø 1.7 Ø 21.8 waters near Wismar, Baltic SeaEpitype-strainWiCoc02

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.

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Materials and methodsThe following material from the Ehrenberg Collectionat the Museum für Naturkunde, Berlin, Germany wasinvestigated:Cocconeis lineata Ehrenberg (1849). Ehrenberg’s materialsand drawings from Lyon (Mica EC 460409-14, Zbl. 2177)and the Genua materials (Mica EC 460401-08, Zbl. 2176),which contain eolian dust (‘Atmosphärische Sphärilen’ inGerman).

Cocconeis euglypta Ehrenberg (1854). Ehrenberg’s mate-rial from Florida, Salakchopko River (EC 210112).

In addition to the type material, new material wascollected and unialgal Cocconeis strains were established.This material is deposited at the Botanischer Garten undBotanisches Museum Berlin–Dahlem (B):Cocconeis lineata. Strain D17_011, voucher B 40 0040-735, from Creek at Lambi, Eysturoy Island, Faroe Islands,Denmark, collected and isolated by J. Bansemer, 8 February2004.Cocconeis euglypta. Strain WiCoc02, voucher B 40 0040-892, from Wismar, Baltic Sea, collected by R. Jahn, 4August 2012 and isolated by O. Skibbe.

For comparison, the epitype strain D36_012 C. placen-tula var. placentula was used (see Jahn et al. 2009).

Water samples were observed under a stereomicroscopeand diatoms were picked out using capillary glass pipettes.Cells were then transferred to 5-cm diameter plastic Petridishes containing culture medium (WC, Chu, AlgaGrow) ofadequate salinity and pH (6.5–7.5). In order to separate cellsand remove attached particles, this treatment was repeatedseveral times, until microscopic inspection confirmed thatpure cultures had been established. Cultures were kept atan ambient temperature of 18–22 ◦C and were illuminated12:12 h with a 39W T5 fluorescent tube (OSRAM LumiluxDaylight) 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 SVand RSV, respectively (Romero & Navarro 1999, Romero2011). Stria density was counted at the center of the valveface and, if the striae were markedly radiate, also at themargin opposite the center of the valve. In the speciesdescription, AA is used for the apical axis, TA for thetransapical axis.

ResultsCocconeis lineata Ehrenberg (Figs 1–8, Tables 1, 3)

Protologue. Ehrenberg 1849, Abhandlungen der Königli-chen 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 (inred) C. lineata on Ehrenberg’s drawing sheet 2177; herereproduced in Fig. 1.

Type locality. Orcan-Staub von Lyon am 17 Oktober 1846[=eolian dust sample collected in Lyon, France, 17 October1846].

Epitype (designated here). Slide B40 0040735, fromstrain 17_011 (Faroe Islands) (Fig. 2).

Epitype locality. Creek at Lambi, Eysturoy Island, FaroeIslands, Denmark, 62.14◦N, 6.71◦E, altitude 40 m above sealevel.

Amended description of Cocconeis lineataElliptical valves (AA: 18.6–22.7 μm; TA: 6.4–13.1 μm).The SV is externally slightly convex toward the narrow,linear/linear–lanceolate sternum, separated from the valveapices by one areola (Figs 3–4). Up to 10 apical striae oneach hemivalve are counted. Striae are uniseriate, (7)10–15in 10 μm, parallel and straight in the valve center, althoughradiate and curved towards the apices. Areolae, 16–24(26)in 10 μm, are externally dash-shaped (Fig. 3), whereas theinternal foramen is ovoid. The valvocopula, open at oneend, lacks fimbriae (Fig. 7). The RSV is externally con-cave and bears a filiform raphe, bordered by a linear narrowsternum with an elliptical or orbicular central area (Fig. 5),proximal and distal raphe ends are coaxial (Fig. 6). RSVstriae are uniseriate, parallel and straight in the valve cen-ter, radiate towards the valve ends (Figs 2, 5, 8), and rangebetween 20 and 28 in 10 μm. Close to the margin, the stri-ation is interrupted by a submarginal hyaline area, whichleaves between one and three areolae separated from therest (Figs 6, 8). The areola foramen is circular or ovoid onboth valve sides (Figs 5–6, 8). The valvocopula, open atone end, is devoid of fimbriae (Fig. 8).

CommentsCocconeis 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. Accord-ing 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 inthe Mikrogeologie (Ehrenberg 1854, pl. 39, part 3, fig. 11),although no description was provided. The Mikrogeolo-gie is, however, a compendium of works published byEhrenberg years earlier. The first two published drawingsunder the name Cocconeis lineata are seen in his work

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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. 2177. Fig. 2. Sternum (left) andraphe–sternum (right) valves from the epitype slide B 40 0040737. 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 loca-tions of the Mediterranean Sea and the Atlantic Ocean inthe 1840s (Ehrenberg 1849). On the mica containing theeolian dust collected in 1846 in Le Verpillière between Lyonand Grenoble, France, only C. atmosphaerica Ehrenberghas been found (≡Diploneis atmosphaerica (Ehrenberg)Jahn & Kusber (Jahn & Kusber 2004)). The mica con-taining the material Ehrenberg received from Genua (Italy)shows, however, no valves of Cocconeis. After check-ing Ehrenberg’s drawing sheets corresponding to the Lyon(Zbl. 2177) and Genua materials (Zbl. 2176), drawingsof C. lineata were found that agree with the figures ofhis 1849 publication. Because Ehrenberg’s drawing of theLyon material has also the name ‘Cocconeis lineata’ writ-ten below the only valve drawn, this drawing was selectedas the lectotype of C. lineata (Fig. 1).

In his revision of Ehrenberg’s type material, Tuji(2009) examined drawings and mica preparation assigned toC. lineata. Unfortunately, Tuji’s lectotypification of C. lin-eata is incorrect. Cocconeis lineata, first mentioned inEhrenberg (1843), has to be considered a nomen nudum

(see above). The next date when Ehrenberg published afigure with this name was from the Lyon and Genua mate-rial (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, supersededby our lectotypification.

According to our own assessment, the only valve ofC. lineata drawn by Ehrenberg measures 29.4 μm (AA) by16.3 μm (TA). The AA:TA ratio for the unique Ehrenberg’sC. lineata valve (1.8) falls within the range measured forthe Faroe clone (1.6–2.0) (Table 3) and matches its averagevery well (1.8, n = 56). Unfortunately, no transapical striaeare recognizable (Fig. 1).

The first published drawing of C. lineata might repre-sent a frustule. Although this is speculative and difficultto 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 asfeatures typical of both valves of C. lineata (Figs 2–8). Asshown by valves from the Faroe Islands, the occurrence of

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a central area is common to the RSV (Figs 5–6) rather thanto the SV (Figs 3–4), whereas the apical lines on both sidesof the raphe–sternum might represent the apical areolae ofthe SV. The submarginal line, as drawn by Ehrenberg sur-rounding the valve almost entirely (Fig. 1), may representsubmarginal thickening of the RSV (Figs 6, 8). Becauseof 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 1893–1903; C. placentula var. euglypta (Ehrenberg) Cleve 1895.

Lectotype (designated here). BHUPM EC 210112-d bl;here reproduced in Fig. 9.

Type locality. Salakchopko River, Florida, USA.

Epitype (designated here). Strain WiCoc02, voucherB 40 0040892, see Figs 10–11.

Epitype locality. Epiphytic on the red alga Ceramiumrubrum in shallow coastal waters, Baltic Sea, pier Bad Wen-dorf, near Wismar, Germany; 53.91◦N, 11.43◦E, altitude0–2 m above sea level.

Amended description of Cocconeis euglyptaElliptical valves (AA: 15.9–29.5 μm; TA: 9.8–17.7 μm).The SV bears about five apical striae with a zigzag lon-gitudinal pattern on each hemivalve (Figs 9–10), concavetoward the narrow, linear sternum (Fig. 12). Striae (18.5–24 in 10 μm) are uniseriate, mostly radiate, more curvedtowards the valve apices (Figs 9, 12), and consist of alveoliwith roundish internal foramina (Figs 13–15). The valvo-copula, open at one end, bears very short digitiform fimbriae(Fig. 15). The concave RSV has a rectilinear raphe, whichends 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, 17–22 in 10 μm, paral-lel in the middle, radiate toward the valve apices, slightlycurved (Figs 11, 16), interrupted by a submarginal hya-line area (Figs 16–18). One or two marginal areolae areslightly separated from those of the valve face by a sub-marginal hyaline area. A small helictoglossa reaches theinternal border of the submarginal hyaline area (Fig. 18).Valvocopula opened with short, slightly laterally expandedfimbriae (Figs 17–18).

CommentsEhrenberg (1853) first mentioned the name C. euglypta in alist of species from Florida. In his Mikrogeologie, he (1854)again provided this name, a picture and some information onits occurrence, albeit that a complete diagnosis is missing.According to the International Code of Botanical Nomen-clature (McNeill et al. 2006), if a name was published with apicture before 1908 this is valid and not considered a nomennudum (see also Jahn & Kusber 2009).

The mica preserving the type material of C. euglyptacontains only one elliptical SV, with up to six apical striaedepicting a zigzag apical pattern (Fig. 9). No RSV is present.For this SV, the measured AA is close to 28 μm, while theTA measures ∼16 μm; striae are around 14 in 10 μm. Thestria density for this unique valve is lower than the valuesobtained for the epitype strain WiCoc02 (Table 3), but itshares the zigzag pattern along the apical axis as well theelliptical to broadly elliptical valve outline (Figs 9–10).

As for many other diatom taxa originally described byEhrenberg (e.g., Jahn & Kusber 2004, Jahn et al. 2009),changes in the systematic status of C. euglypta have beenproposed over time. These taxonomic changes are possiblyrelated to the morphological similarity between C. euglyptaand C. lineata, as well as to the incomplete characteri-zation of both diatoms when initially described. Grunowproposed C. euglypta as a variety of C. lineata (Grunow inVan Heurck 1880), while Héribaud (1893–1903) introducedC. rouxii var. euglypta.

The first appearance of C. euglypta as a variety of C. pla-centula is that of Grunow (1884). As for C. lineata, thecombination C. placentula var. euglypta became commonin the following decades (e.g., Cleve 1895, Hustedt 1930,Germain 1981, Suzuki & Nagumo 2002), without furtherdiscussion of the main morphological features of their valverelating C. lineata and C. euglypta to C. placentula var. pla-centula. For example, Hustedt (1930) pictured C. euglyptawithout explicitly citing or describing C. placentula var.placentula. Some later authors subsumed both C. lineataand C. euglypta as varieties of C. placentula (e.g., Germain1981, Holmes et al. 1982). Subsuming several varieties,however, tends to blur understanding of the nominate vari-ety, here var. placentula, which presents the original conceptof the species (Jahn et al. 2009). Only in recent decades hasthe nominate variety been picked up again and a few picturesare presented which are supposed to represent C. placen-tula var. placentula (e.g., Patrick & Reimer 1966, Krammer& Lange-Bertalot 2004, Kobayasi et al. 2006, Jahn et al.2009).

DiscussionThe occurrence of valves with transitional morphologybetween C. lineata and C. euglypta has been argued as animpediment for distinguishing both as separate taxa (e.g.,Geitler 1927, 1932, Foged 1977, Germain 1981). Several

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Figs 9–18. 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 210112-d bl. Figs 10–18. Monoclonal culture,strain WiCoc02; epitype slide B 40 0040892. 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 valveshowing short fimbriae (arrows) and open end of valvocopula (asterisk). Fig. 16. Raphe–sternum valve. Fig. 17. Entire raphe–sternumvalve showing open end of valvocopula. Fig. 18. Raphe–sternum valve showing detail of raphe, helictoglossa, areolae, valvocopula andfimbriae (arrows). Scale bars = 10 μm (Figs 9–12, 14, 16–17), 2 μm (Figs 13, 15), 1 μm (Fig. 18).

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Fig. 19. Relation between the number of striae measured in thecentral valve part at margin and the AA:TA ratio of sternum valveof C. lineata (red dots) and C. euglypta (gray crosses) from thetwo epitype strains. The regression represent linear fittings foreach epitype strain.

studies have discussed the difficulties in distinguishingbetween C. euglypta and C. lineata and in distinguish-ing them from other morphologically related varieties ofC. placentula. For example, Patrick & Reimer (1966) pro-posed that the ratio between the apical and transapical axes(AA:TA in Fig. 19) varies more in C. euglypta than inC. lineata. Our observations do not support this statement(Table 3). However, when the number of SV striae is plottedagainst the AA:TA ratio (Fig. 19), differences in morphom-etry between both taxa are seen. In spite of some valuesoverlapping and the similarity in the AA:TA ratio of bothtaxa (Table 3), the density of the transapical striae seemsa reliable character. Although the valves C. lineata andC. euglypta show similarities in their overall morphology,the morphometry of their valves supports the separation ofboth taxa (Fig. 19, Table 3).

Monnier et al. (2007) argue that a certain degree of con-fusion in the basic concept of C. lineata and C. euglypta isdue to the fact that many diatom floras present micrographswithout the addition of the pertaining description and mor-phometric data (Tables 1–2). The presence of up to six apicalstriae on each hemivalve is an easily recognizable struc-tural feature of the SV of C. euglypta (Figs 9–10, Table 2),whereas six to ten apical striae seem to be the rule in SVof C. lineata (Figs 2–4, Table 1). It is speculated that thisconfusion partially relates to different ranges of apical striaeas reported by different authors. The density of apical striaein our strain of C. euglypta matches the range reported inVan Heurck (1885), although it is slightly lower than otherreported values (up to six, Patrick & Reimer 1966, Dexi-ang et al. 1985, Suzuki & Nagumo 2002), and falls withinthe range given by Krammer & Lange-Bertalot (1991, threeto ten). Regardless of the number of apical striae, the typ-ical zigzag apical areolar arrangement can be recognizedas a constant feature among different descriptions (Dexianget al. 1985, Krammer & Lange-Bertalot 1991).

Because of the lack of important morphological dif-ferences between the RSV of C. lineata (Figs 2, 5–6)and C. euglypta (Figs 11, 16–17), respective descriptionshave hardly considered its characteristics (Tables 1–2).The similar overall morphology of the RSV of C. lineataand C. euglypta and the occurrence of a submarginal hya-line ring (Figs 5–6, 16–17) morphologically both relate toC. placentula var. placentula (see Figs 28, 30, and 37–39in Jahn et al. 2009).

Our research on Cocconeis followed a purely morpho-logical approach. The morphological and morphometricvariability presented in our study is based on observationsof valves grown under controlled laboratory cultures of asingle clone. Monnier et al. (2007) argued that the over-all aspects of SV of C. lineata and C. euglypta stronglyvary under different ecological conditions, and concludedthat both species respond differently under different nutrientsupply. Studying populations of Cocconeis collected in theRhine–Meuse basin (northwest France) between 2000 and2005, Monnier et al. concluded that C. lineata is typicalof oligotrophic waters, whereas C. euglypta is ubiqui-tous, 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 StriaeTaxon n (μm) (μm) TA (μm) (μm) ratio Avg ± SD (in 10 μm) Avg ± SD

C. placentula epitypestrain D36−012

21 12.60–33.3 23.30 ± 7.04 7.90–24.6 12.70 + 4.12 1.34–1.73 15.2 ± 4.9 15–25 21 ± 2.09

C. lineata epitypestrain D17−011

56 18.57–22.67 21.17 ± 1.01 6.40–13.08 11.37 ± 1.21 1.63–2.07 1.84 ± 0.09 12–20 16.50 ± 2.34

C euglypta epitypestrain WiCoc02

31 15.90–29.50 18.30 ± 2.24 9.80–17.60 11.15 ± 0.54 1.54–1.76 1.65 ± 0.05 20–24 21.77 ± 1.02

Notes: n: numbers of specimens studied; AA: apical axis; TA: transapical axis; Avg: average; SD:, standard deviation.

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Typification of two taxa of Cocconeis Ehrenberg 9

supports different pollution levels (Monnier et al. 2007).Together with the morphological observations presentedhere, the consideration of ecological conditions seems to beequally helpful when trying to distinguish between C. lin-eata and C. euglypta. The habitats of the epitypes areeither oligotrophic (C. lineata) or high-conductivity waters(C. euglypta).

Concerning the type locality of the epitypes, it wouldhave been preferable to designate strains from the typelocalities. For C. lineata, it is ‘dust at Lyon’ and there-fore could be any place; for C. euglypta, it is a river inFlorida (USA). Because the current concept is European, itwas decided to use available European cultures, which havesimilar morphology and ecology. Nowadays, it is becomingimportant to designate epitypes – explanatory types – whichsupport the current concepts and offer micro-morphologicalas well as molecular data in order to establish referencelibraries with DNA barcodes for molecular identification(Zimmermann et al. 2011, Pawlowski et al. 2012).

Whether C. lineata and C. euglypta should keep the rankof a species is still a matter of debate. In view of the mor-phological differences among C. lineata and C. euglypta(Table 3), and C. placentula var. placentula as well as otherCocconeis species with a Cocconeis placentuloid-like mor-phology (O. Romero & M. De Stefano, unpubl.), we proposeto keep both taxa at the species rank. Ongoing molecu-lar research on several clones collected from European andEast Asian localities will hopefully allow us to answer thisquestion and solve this taxonomic uncertainty.

AcknowledgementsWe gratefully acknowledge the help of Jana Bansemer withcollecting and culturing diatoms, of Monika Lüchow at the SEM(both at the Botanic Garden and Botanical Museum Berlin), andof 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 theEhrenberg Collection as part of the AlgaTerra project as well asthe data mobilization for GBIF. OER was partially supported bythe Spanish Council of Scientific Research and by the Synthesys

Project (DE-TAF-1136), which is funded by the European Com-munity Research Infrastructure Action under the FP6 ‘Structuringthe European Research Area Programme’.

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