European Journal of Taxonomy 204: 1-18

http://dx.doi.org/10.5852/ejt.2016.204

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2016 • Riaux-Gobin C. et al.

Research article

Cocconeis molesta Kiitz., C. diaphana W.Sm. and C. dirupta W.Greg.

(Bacillariophyta): type material, ambiguities and possible synonymies

Catherine RIAUX-GOBIN 1 - 2 -*, Pierre COMPERE 3 , Richard W. JORDAN 4 ,

Michel COSTE 5 & Jovita C. YESILYURT 6

1 CRIOBE-USR 3278 CNRS-EPHE-UPVD, 66000 Perpignan, France.

2 Laboratoire d’Excellence ‘CORAIL’, 66000 Perpignan, France.

3 Deceased 29 April 2016. Former address: Botanic Garden Meise,

Domein van Bouchout, 1860 Meise, Belgium.

4 Department of Earth & Environmental Sciences, Yamagata University, Yamagata 990-8560, Japan.

5 IRSTEA, 50 avenue de Verdun, Cestas, France.

6 The Natural History Museum, Department of Life Sciences, Cromwell Rd,

SW7 5BD, London, United Kingdom.

* Catherine. gobin@univ-perp. fr (corresponding author)

4 sh 081 @kdw.ki.vamagata-u.ac.ip

5 [email protected]

6 [email protected]

Abstract. F.T. Ktitzing introduced Cocconeis molesta with only an uninformative description and a

poor illustration: C. molesta has small, oblong valves and is an epiphyte. Another species, Cocconeis

diaphana , described by William Smith, is said to have larger valves than C. molesta , with frustules

that are relatively oblong. Smith described two forms: one with a distinct fascia on its raphe valve

(var. P), the other without this feature. A third species, Cocconeis dirupta was described by Gregory,

who expressed doubts that it differed from C. diaphana. Finally, Cocconeis molesta var. crucifer a

Grunow was first introduced in Van Heurck’s Atlas but was subsequently treated by Van Heurck as a

synonym of C. molesta. No previous account has examined the type material of these species. In this

paper, we undertake that task and examine type slides and raw material in order to discriminate these

different taxa. We conclude by recognizing three species: Cocconeis molesta Kiitz., C. diaphana W.Sm.

and C. dirupta W.Greg. Cocconeis diaphana var. p is considered to be a synonym of C. dirupta and

C. molesta var. crucifera is considered to be a synonym of C. molesta. Lectotypes are designated for

C. diaphana and C. dirupta.

Keywords. Cocconeis molesta , Cocconeis diaphana , Cocconeis dirupta , synonymies, types.

Riaux-Gobin C., Compere P., Jordan R.W., Coste M. & Yesilyurt J.C. 2016. Cocconeis molesta Kiitz., C. diaphana

W.Sm. and C. dirupta W.Greg. (Bacillariophyta): type material, ambiguities and possible synonymies. European

Journal of Taxonomy 204: 1-18. http://dx.doi.org/10.5852/ejt.2016.2Q4

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European Journal of Taxonomy 204 : 1-18 ( 2016 )

Introduction

The diatom genus Cocconeis Ehrenb. (Ehrenberg 1837: 173) is diverse, comprising numerous small

species, several of which are very similar and difficult to identify. Thus, there is a need to re-examine the

type material in order to improve, clarify and expand the original descriptions and to determine whether

or not these taxa are synonymous. Unfortunately, most diatom species are identified by comparing

specimens collected from places other than the type locality. However, in the case of Cocconeis , studies

on the type material have been increasing (Jahn et al. 2009; Romero 2011; Riaux-Gobin et al. 2014a,

2014b; Romero & Riaux-Gobin 2014), particularly the detailed examination of raw type material with a

scanning electron microscope (SEM) (e.g. Romero & Riaux-Gobin 2014).

Herein, we focus on Cocconeis molesta Kiitz., Cocconeis diaphana W.Sm., Cocconeis dirupta W.Greg.

and some other taxa pertaining to the same group, all of which are small and very similar in morphological

characteristics (under LM), and may have led to taxonomic confusion in the past (see Discussion).

Taxonomic history of Cocconeis molesta Kiitz., Cocconeis diaphana W.Sm.,

Cocconeis dirupta W.Greg. and allied taxa

Cocconeis molesta Kiitz. was introduced along with a poor illustration and very succinct description,

which mentioned only the small size and oblong shape of the frustule and that it was epiphytic on

Callithamnion cruciatum (C.Agardh) Nageli (Kiitzing 1844: 71, pi. 5, fig. 7, reproduced in Fig. 1).

Another species with a relatively oblong frustule but with larger dimensions than C. molesta was

subsequently described as Cocconeis diaphana W.Sm. (Smith 1853: 22, pi. 30, fig. 254, reproduced in

Figs 2-3), and included two varieties; one without a distinct fascia and the other with a conspicuous

fascia (p), with the latter accompanied by a laconic note stating “p. Nodule dilated into a stauros”.

These forms will be cited hereafter as var. diaphana and var. p. Two varieties, corresponding more or

less to var. diaphana and var. p, were later described as C. diaphana var. amygdalina Grunow ex Cleve

(Cleve 1895) without a fascia, and C. diaphana var. dirupta (W.Greg.) Rabenh. (Rabenhorst 1864) with

a distinct fascia, respectively.

Cocconeis dirupta W.Greg. was introduced with some doubt about how it differed from C. diaphana

(Gregory 1857: 491, pi. 9, fig. 25, reproduced in Fig. 4), with C. dirupta described as brown colored with

conspicuous striae, while C. diaphana (noted by Gregory as also present in his material, see C. dirupta

type material discussion) was diaphanous (cf. Gregory 1857: 491).

Lastly, Cocconeis molesta var. crucifera Grunow ex Cleve was invalidly described in Van Heurck

(1880-1885: pi. 30, figs 20-23, reproduced in Figs 5-8) and afterwards classified as a synonym of

C. molesta by Van Heurck (1896: 291, pi. 29, fig. 823). Van Heurck (1896) examined C. molesta type

material, from the isotype present in his collection (. Kiitzing 259 ) and noticed the stauros on the raphe

valve and produced drawings identical to those first illustrated as C. molesta var crucifera in Van Heurck

(1880-1885: pi. 30, figs 22-23).

Most of the above cited taxa (see further comments below), have been described with a fascia (or

stauros), particularly on their raphe valve, and have poor original descriptions. Although several studies

have contributed to a better understanding of these taxa, unresolved problems still remain, while other

studies have provided revised descriptions that did not include observations on the types (e.g. about

C. dirupta'. Hustedt 1931-1959; Foged 1978; Kobayasi & Nagumo 1985; Sar et al. 2003; Riaux-Gobin

r

et al. 2011; Lobban et al. 2012; about C. diaphana'. Alvarez-Bianco & Blanco 2014; about C. molesta

var. crucifera : De Stefano et al. 2000; Sar et al. 2003).

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RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dirupta

We here examine several original materials that were cited in the protologues in order to discriminate

different taxa, clarify their definitions and resolve their nomenclatural issues, including synonymies,

confirmation of types and designation of a lectotype for Cocconeis diaphana.

Material and methods

Materials used in this study derived from several sources:

(1) Friedrich Traugott Kiitzing collection, no. 259, type material of Cocconeis molesta Kiitz., from

Venedig, collector F.T. Kiitzing; herbarium specimen (BM 000905975) with raw material in mica;

slide (BM 18381 made from the same 259 material) in collection, both housed in the Natural History

Museum, London (BM). This material is type material. Fig. 9.

(2) Henri Ferdinand Van Heurck collection, slide IX-43-A13 labelled Cocconeis molesta Kg

Mediterranee Kiitzing no. 259, probably mounted by H. Van Heurck from the collection no. 259

of Kiitzing, collected on Callithamnium cruciatum , housed in the Van Heurck collection, Botanic

Garden Meise (BR). The slide BM 18381 (see above) was also made using the Kiitzing type material

(no. 259); Van Heurck’s slide is an isotype. Fig. 10.

(3) William Smith collection, no collection number (mounted in 1887, unknown mounter), Pontac,

Jersey, Aug. 1852, type material of Cocconeis diaphana W.Sm.: slides BM 23161 (Fig. 11) and

BM 23162, all housed in BM.

Figs 1-8. Original drawings. 1. Cocconeis molesta Kiitz. (Kiitzing 1844, pi. 5, fig. 7). 2-3. Cocconeis

diaphana W.Sm. (Smith 1853, pi. 30): 2. var. (3. 3. type C. diaphana war. diaphana. 4 . Cocconeis dirupta

W.Greg. (Gregory 1857, pi. 9). 5-8. Cocconeis molesta var. crucifer a Grunow ex Cleve (Van Heurck

1880-1885, pi. 30): 5-6. f. minor. 7-8. f. major.

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European Journal of Taxonomy 204: 1-18 (2016)

(4) Freeman Clarke Samuel Roper collection, no. 1212, material of Cocconeis diaphana W.Sm. (with

an almost illegible round red label), Sidmouth (the inscription “WS 254” written by diamond pen in

reference to fig. 254 of the W. Smith Synopsis). Collector W. Smith, slide BM 19589 housed in BM.

Fig. 12. This material is assumed to be a syntype.

(5) Henri Ferdinand Van Heurclc collection, no. VI-45-B10 (housed in BR, Fig. 13), W. Smith material

mounted by W. Smith's nephew, Charles Coppock. Determined by W. Smith as Diatomaceae,

Cocconeis diaphana (written on a round red label). The inscription “WS 254” (see above) was

written by diamond pen on the slide: (3, Sidmouth, along with the mention. Collector “Miss Cutler,

communicated by Dr Greville” (Catherine Cutler of Sidmouth (1784-1866) was a distinguished

algologist). This slide is considered to be an isosyntype.

(6) Robert Kaye Greville collection, material of Cocconeis dirupta W.Greg., from Arran 56: slide BM

1420, Fig. 14 (no diamond ringed specimens). Type specimens were neither indicated by W. Gregory

or R.K. Greville since this was not required at that time; a curator of BM (see label on the left side

of the cover slip; specimen probably identified by Robert Ross) assumed this to be an isotype of

Cocconeis dirupta ; in fact this is a syntype.

The diatoms on the permanent slides were observed with (1) an Olympus BX51 microscope, equipped

with a colorview camera (National Botanic Garden, Meise, Belgique) and (2) a Zeiss Axiophot 200

microscope with differential interference contrast (DIC, obj. 100 x 2.5) and photographed with a Canon

PowerShot EOS1000D digital camera (CRIOBE, Perpignan, France). A comparison of morphological

features and biometric data of the type slide taxa are provided in Table 1.

Figs 9-14. Illustration of the type slides. 9. Cocconeis molesta Ktitz.: F.T. Kiitzing collection, no. 259,

BM 18381.10. Cocconeis molesta: H.F. Van Heurck collection, no. IX-43-A13.11. Cocconeis diaphana

W.Sm.: W. Smith collection, “Jersey, Pontac” August 1852, BM 23161. 12. Cocconeis diaphana:

F.C.S. Roper collection, “Sidmouth”, no. 1212, BM 19589. 13. Cocconeis diaphana: H.F. Van Heurck

collection, “Sidmouth”, no. VI 45B10. 14. Cocconeis dirupta W.Greg.: R.K. Greville collection, Arran

56, BM 1420.

4

Table 1 . Comparison of morphological features and biometric data of the examined type slide taxa.

RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dinipta

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European Journal of Taxonomy 204: 1-18 (2016)

Terminology and abbreviations

For the description of the frustule, terminology follows Anonymous (1975), Ross et al. (1979) and

Round et al. (1990). As previously proposed, in particular by Riaux-Gobin et al. (2013), we designate

the valve with a raphe as the raphe valve (RV) and the valve without a raphe as the sternum valve (SV).

Since some of the original raw material used by F.T. Kiitzing has been found, whereas the same was not

possible for W. Smith, R.K. Greville and W. Gregory, scanning electron microscope (SEM) observations

have been made on only one type material. Nevertheless, modern light microscopy allows the striation

and other valve features to be observed on the type slides, so that the original description can be emended.

Results

Class Bacillariophyceae Haeckel emend. Medlin & Kaczmarska (Medlin & Kaczmarska 2004)

Subclass Bacillariophycidae D.G.Mann in Round et al. (Round et al. 1990)

Family Cocconeidaceae Kiitz. (Kiitzing 1844)

Cocconeis molesta Kiitz. (Kiitzing 1844)

Figs 1, 15-20, Table 1

Cocconeis molesta var. crucifera Grunow ex Cleve (1895: 174). Type: pi. 30, fig. 23 in Van Heurck

(1880-1885).

Original description

Kiitzing (1844): 71, pi. 5, fig. 7. 1-2, reproduced in Fig. 1

“C. minuta, elliptico-oblonga, densissime aggregata, laevissima; limbo nullo. An Callithamnion

cruciatum in den Lagunen von Venedig ! (Laguna Veneta, Italy) - Lange 1/150-1/140”. - “fig. 1.

gegliiheten Exemplare, fig. 2. aufgeweichte Exemplare”.

Emended description by Van Heurck

Van Heurck (1896: 290, pi. 29, fig. 823) after observation of the original specimen (F.T. Kiitzing no. 259

in Van Heurck collection): “valves small, elliptic, finely striate; transverse striae about 40 in 1 c.d.m.,

reaching to the raphe, formed of puncta, distant and consequently capable of forming longitudinal lines

undulate or decussate (according to the direction of the illumination). Raphe robust; central nodule

elongated into a narrow acute stauros. Length, 1.5 to 2 c.d.m. Breadth, 1 c.d.m. Marine. North Sea”.

Type material

“An Callithamnion cruciatum in den Lagunen von Venedig” (Kiitzing 1844: 71; Kiitzing 259, Herbarium

sheet BM 000905975, BM 18381, holotype); BR slide IX-43-A13 (Van Heurck collection, Kiitzing 259,

isotype).

Notes

Van Heurck (1896) after studying material from F.T. Kiitzing, emended the description and stated that

the observed specimen “corresponds to the var. crucifera of Grunow (H.V.H. Atl.: pi. 20, fig. 20)”

(Van Heurck 1880-1885: pi. 30, fig. 20) and added “it appears to me right to consider it as the type

form”.

LM examination of the type material and completed description

Cf. Riaux-Gobin & Compere (2008): figs 56-57; Figs 15-17 from BM 18381, Figs 18-20 from slide

IX-43-A13.

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RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dirupta

The frastule is small (ca. 16.4 pm long, 9.7 pm wide) and strongly arched (RV concave, SV convex).

The RV striation is hardly discernible, with ca. 30 striae in 10 jam (Fig. 18, arrowhead). The SV

areolae are arranged along axial rows in a zig-zag pattern (22-23 rows in 10 pm. Figs 16, 17, 20). The

helictoglossae are close to the margin and deflected in opposite directions (Fig. 15), the raphe is straight.

The SV sternum is narrow and straight, with a small oblong central area. The RV fascia is narrow and

half a valve in length.

SEM examination of the Herbarium sheet BM 000905975

The material is very poor and only a broken S V of Cocconeis molesta was observed, with the following

morphometries and features: estimated valve length (> 17 pm), SV stria density (40-42 in 10 pm.

Figs 15-20. Cocconeis molesta Kiitz. 15-17. From BM 18381 (15-16: holotype illustration);

helictoglossae deflected in opposite directions (15, arrowheads), SV axial rows in a zig-zag pattern

(16-17). 18-20. From IX-43-A13 (H.F. Van Heurck collection), RV striation often difficult to observe

(18, arrowhead), RV fascia (19, arrowheads), SV axial rows in a zig-zag pattern (20). Scale bars =

10 pm.

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European Journal of Taxonomy 204: 1-18 (2016)

areolae small and transversely oblong), apical SV row of areolae, in a zig-zag pattern (27.5 in 10 pm),

SV sternum narrow and thickened in internal view, central area slightly enlarged.

Cocconeis diaphana W.Sm. (Smith 1853)

Figs 2-3, 21-34, Table 1

Cocconeis molesta var. amygdalina Grunow ex Cleve (1895: 174).

Cocconeis amygdalina Breb. ex Grunow in Van Heurck (1880-1885: pi. 30, figs 22-23), nom. inval.

Original description

Smith (1853): 22, pi. 30, fig. 254, reproduced in Figs 2-3.

“Cocconeis diaphana , n. sp. V. elliptical, scarcely siliceous, diaphanous; striae obscure. Length .0012”

to .0018” (30.48 to 45.72 pm), v.v. (3 Nodule dilated into a Stauros. Marine. Sidmouth, Miss Cutler,

communicated by Dr. Greville. Pontac, Jersey, Aug. 8, 1852, W. Sm. Supp. Plate XXX. 254”.

Type material

“Marine. Sidmouth, Miss Cutler...” “Pontac, Jersey... W. Sm.”, syntypes; “Pontac, Jersey... W. Sm.”,

BM 23161, here designated as lectotype; BM 23162, isolectotype; The other syntype, BM 19589, from

Sidmouth, belongs to C. dirupta Gregory.

Notes

When W. Smith introduced C. diaphana , he also proposed an unnamed variety (3 characterized by

“the nodule dilated into a stauros”. This variety, mostly represented in the Sidmouth gathering,

though originally a syntype must be excluded from this species. It will be here treated as belonging to

C. dirupta W.Greg. (see further comments under this species). The original drawings of C. diaphana

(Smith 1853, fig. 254) show relatively oblong valves, one without any stauros, the other, marked (3, with

a distinct stauros on the RV.

Van Heurck (1896: pi. 29, fig. 823bis) reports Cocconeis molesta var. amygdalina as a “synonym of

C. diaphana W.Sm. partim , S.B.D., i., p. 22, pi. 30, fig. 254; H.V.H. Atl., pi. 30, figs 5 and 35”, and

comments that it is: “much larger in size, 3.5 to 4.5 c.d.m. (35 to 45 pm). Central nodule rounded,

surrounded by small hyaline area. Marine [...] Jersey (W.Sm.)”.

Description of specimens from “Jersey, Pontac”, after LM examination of the type material

BM 23161 (Figs 21-26) contains oblong-elliptical, thinly silicified and diaphanous valves, 33—42 pm

(38 pm ± 2.5 a) long, 21-26 (23 pm ± 2.2) wide, 1/L 1.65 ± 0.2, with 26 ± 2.2 SV striae in 10 pm,

25 ± 0.7 RV striae in 10 pm, and ca. 23 axial SV rows in a zig-zag pattern (Fig. 26). The SV sternum is

straight and narrow, the central area very reduced (Figs 23-24). The RV has clearly identifiable striae,

with 25 areolae in 10 pm. The RV fascia is short and quite high, with the aspect of an elliptic central

area more than a real fascia. The helictoglossae are straight and off the margin (Fig. 24). As this slide

(BM 23161) contains the specimen best matching the original description, we here designate it as the

lectotype of C. diaphana W.Sm.

Remark

Thanks to the kindness of Bart Van de Vijver we have received several SEM photographs of the

isolectotype of Cocconeis diaphana deposited in the Van Heurck collection in Meise (BR). This material

is epiphytic on marine Rhodophyceae, and is present on a mica labelled “ Cocconeis diaphana n.sp.,

Jersey, Aug. 14. 1852”, preserved in the W. Smith collection, vol. I, p. 33. These SEM photographs

(Figs 39—44) are a perfect match for the LM figures in this paper and support our emended description.

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RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dirupta

Figs 21-26. Cocconeis diaphana W.Sm. var. diaphana from BM 23161, “Jersey, Pontac”. 23. Lectotype

illustration. SV sternum narrow and straight (21-22), SV central area small (21, arrow), SV axial rows

in a zig-zag pattern (21-22, 26). RV striation easily discernible and beaded (23, arrowhead), RV central

area transapically enlarged but short (24, arrows), proximal raphe endings robust and close (25). Scale

bars = 10 pm (21-25), 5 pm (26).

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European Journal of Taxonomy 204: 1-18 (2016)

Figs 27-34. Cocconeis diaphana W.Sm. “Sidmouth” (var. P). 27-32. From VI-45-B10 (H.F. Van

Heurck collection). One SV stria lacking on one side, or both sides (27, arrow, 28-29), RV fascia narrow

and extended (30, arrowheads), raphe slightly sigmoid (31, arrowhead), proximal raphe endings robust

(30-32). 33-34. From BM 19589, SV sternum in two lanceolate parts (33, arrowhead), helictoglossae

deflected in opposite directions (34, arrowheads). Scale bars =10 pm.

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RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dirupta

Description of specimens from “Sidmouth”, after LM examination of the type material

The Van Heurck collection (VI-45-B10, Figs 27-32) has specimens that are 15-24 pm (20.5 ± 3.2 o)

long, 14-18.3 (16 ± 2.4) wide, 1/L 1.28 ± 0.1, with 18.7 ± 1.1 SV striae in 10 pm, and 22.7 ± 2.2 RV

striae in 10 pm. Slide VI-45-B10 only shows the var. (3.

The W. Smith collection (BM 19589, Figs 33-34) has specimens that are 19-26 pm (22 ± 2.9 o) long,

16-20 (18.6 ± 2) wide, 1/L 1.19 ± 0.05, with 20 ± 1.4 SV striae in 10 pm, and 22 ± 0.5 RV striae in 10 pm.

Valves round-elliptical, relatively small. The SV is coarsely striated and punctuated, usually with no

axial rows of areolae. The SV sternum is large and composed of two lanceolate parts (Figs 27-29,

33), one median SV stria lacking on one side (Fig. 27, arrow) or both (Fig. 33). The RV has coarsely

punctuated striae, strongly radiate. The RV fascia is narrow and wide (often more than half a valve

in length). The raphe is often slightly sigmoid with helictoglossae deflected towards opposite sides

(Fig. 34). Slide BM 19589 only shows the variety (3.

The two examined slides of “C. diaphana Sidmouth” (VI-45-B10/BR and BM 19589) show valves

with similar characteristics (Figs 27-34, 33-34), close to those of Cocconeis dirupta W. Gregory

(Figs 35-38, see below). Therefore, var. [3 is here excluded from C. diaphana and considered as a

synonym of C. dirupta.

Cocconeis dirupta W.Greg. (Gregory 1857)

Figs 4, 35-38, Table 1

Cocconeis diaphana W.Sm. var. p (“Sidmouth material”).

Original description

Gregory (1857): 491, 492, pi. 9, fig. 25 reproduced in Fig. 4.

“Broad short oval to orbicular. Length 25.4 to 61 pm; breadth 17.8 to 53.3 pm”. “Valve thick. Median

line irregular, like a slit. Wavy longitudinal striae, except the slit. Fine transverse striae. Appearance of

a long stauros, which, under a higher power, disappears as such. The striated surface seems to be Torn

asunder in the middle’. Vertical striae about 26, transverse striae about 60 in 1 c.d.m.”.

Type material

Lectotype, designated here: slide BM 1420, labelled “Arran 56” in Greville collection, the only syntype

found in BM.

Notes

Several localities (Glenshira sand, Mr Miles’s Corallina gathering and several dredgings) cited by

Gregory in the original description could contain syntypes, but only the one designated as lectotype was

found in BM. According to W. Gregory “C. diaphana [...] which was found occurring with C. dirupta

[...] may perhaps be an imperfect form of C. dirupta [...] or possibly [...] the lower valve’ of the

latter”, with some further notes that “it is, however equally probable that these forms belong to different

species”.

LM examination of the type material and completed description

Figs 35-38, from BM 1420: n = 16, valves are 18.3-36.5 (20 ± 6) pm long, 17.2-30.8 (26.6 ± 4.7) pm

wide; with 13.5-19.5 (16.6 ± 2) SV striae in 10 pm, and 16-23 (18.9 ± 1.9) RV striae in 10 pm. L/l:

1.12 ± 0.06. Valves thick, round-elliptic to almost discoid. Valves rarely found separate, appearing dark-

brown. S V with coarse radiate striae, equidistant, composed of transapically oblong areolae arranged in

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European Journal of Taxonomy 204: 1-18 (2016)

a zig-zag pattern along longitudinal lines, areolae smaller near the margin. One median stria often shorter

on one side of the central area (Figs 35-36, arrows). Presence of intercalary short striae near the margin.

SV sternum relatively large, fusiform (rarely constricted in its mid-part) with apices often deflected in

opposite directions (not illustrated). RV with delicate but clearly identifiable striae, equidistant, strongly

bent at the apices, with frequent intercalary short striae near the margin. Raphe almost straight to slightly

sigmoid (Fig. 37). RV axial area narrow. Distal raphe fissures close to the margin. Helictoglossae often

clearly deflected in opposite directions (Fig. 37, arrowheads); presence of a large and narrow transverse

fascia (never reaching the margin, formed by one or two shorter striae. Fig. 38, arrows); proximal raphe

endings coarse and relatively close.

Figs 35-38. Cocconeisdirupta^N. Greg. fromBM 1420.37. Lectotype illustration. SV sternum lanceolate

with apices slightly bent in opposite directions (36), one SV stria lacking on one side (35, 36, arrow), RV

striae strongly radiate, RV fascia narrow and extended (38, arrows), helictoglossae deflected in opposite

directions (37, arrowheads) and raphe slightly sigmoid (37). Scale bars = 10 pm.

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RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dirupta

Figs 39-44. Cocconeis diaphana W.Sm. isolectotype SEM illustration. Mica labelled as “ Cocconeis

diaphana n.sp., Jersey, Aug. 14. 1852”, deposited in the Van Heurck collection in Meise (BR). SV external

view with a reduced central area (39, arrow) and striae composed of transversally elongated alveoli (39).

SV internal view (40). Note the SV valvocopula (SVVC) with a smooth edge (40, arrowhead). Detail

of the SV apex (41). Detail of a broken SV showing the double layered structure of the alveoli (42).

RV external view with the central oblong-elongate central area reaching less than !4 of the valve width

(43, arrow). RV internal view with a low and straight helictoglossa (44, arrow) and the RV valvocopula

(RVVC) with a smooth edge (44, arrowhead). Scale bars =10 pm (39, 40, 43-44), 2 pm (41), 1 pm (42).

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European Journal of Taxonomy 204: 1-18 (2016)

The complete frustules appear obscure while the separate RV and S V appear translucent, which probably

justifies W. Gregory’s hesitation about the existence of a second taxon (C. diaphana W.Sm.) in his

material. On the other hand the R.K. Greville drawing (Gregory 1857: fig. 25) probably superimposed

the two valves. Contrarily to the latter drawing (Gregory 1857, fig. 25 reproduced in Fig. 4), the fascia

does not reach the valve margin in the many specimens observed in this study.

The slide BM 1420 from Arran 56 (Gregory in Greville collection) is designated here as the lectotype,

since nothing else has been traced that could be considered as original material studied by W. Gregory.

Discussion

Ambiguities and synonymies

The type of Cocconeis molesta has unique features and morphometries (as discussed above) that cannot

be confused with those of C. diaphana. Cocconeis molesta has small dimensions, a wide fascia, RV

striae that are hardly discernible ( ca. 30 in 10 pm), and helictoglossae close to the margin and bent in

opposite directions.

Nevertheless, several recent papers refer to Cocconeis molesta as C. cf. molesta (e.g. Bruder & Medlin

2007; Baldi et al. 2011) which shows the difficulty in accurately defining this taxon. Although Cocconeis

molesta is rarely illustrated in publications, ambiguities have been noticed when analyzing some of the

images: da Silva (1946, fig. 91) presents a drawing of a large RV fascia; an SV is seen in the LM (at

http://www.diatomloir.eu/Site%20Diatom/Sardiadeux.html ). with a much bigger one corresponding to

the RV; Majewska et al. (2014, pi. 2, fig. 13) showed the species in SEM with morphometries (from

fig. 13: ca. 57 pm long, 30 pm wide, with ca. 18 striae in 10 pm) but it might be Cocconeis diaphana

var. diaphana.

On the other hand, the taxon Cocconeis molesta var. crucifera has been abundantly illustrated in both

EM and SEM (e.g., Kobayasi & Nagumo 1985; De Stefano et al. 2000; Sar et al. 2003) though the type

material for this taxon has apparently not been checked nor compared with that of C. molesta.

Therefore, it is very likely that the images and illustrations in these references actually belong to

Cocconeis molesta , with C. molesta var. crucifera being a synonym.

The specimens of Cocconeis diaphana from “Jersey, Pontac” (Figs 21-26) and from ‘Sidmouth’

(Figs 27-34) obviously pertain to two distinct taxa. Smith (1853) originally stated that there were two

forms, but without indicating their respective origins. The present study shows that the specimens

found in the “Jersey, Pontac” sample do fit the concept of Cocconeis diaphana var. diaphana (oblong

shape, reduced RV transverse central area), while the specimens from “Sidmouth” (with a round to

sub-orbicular shape and a wide fascia) belong to the unnamed variety p which was later included as a

synonym of C. dirupta by several authors (e.g., Cleve 1895; Hustedt 1931-1959). Cocconeis diaphana

var. (3 and C. dirupta have very similar features (Figs 27-38), except for the general shape of the valve

illustrated in the original drawings, with C. diaphana var. (3 being more elliptical. The conspicuous striae

characterizing C. dirupta were not illustrated in the original drawing of C. diaphana var. [3 (Fig. 2), but

the two taxa may still be conspecific.

In the original drawings and descriptions of Cocconeis dirupta and C. diaphana var. (3 there was no

indication of a sigmoid raphe, which slightly contradicts our own observations on the original material

of C. dirupta and C. diaphana var. [3 (as discussed above).

r

Recently, Alvarez-Bianco & Blanco (2014) proposed that C. dirupta and C. molesta var. crucifera are

synonymous with C. diaphana , not by examining the type material, but based on the fact that the raphe

14

RIAUX-GOBIN et al ., Cocconeis molesta, Cocconeis diaphana and Cocconeis dirupta

is straight in all of the original illustrations of these taxa. However, after type examinations, Cocconeis

dirupta has a slightly sigmoid raphe. Furthermore, Cocconeis dirupta , C. molesta and C. diaphana

var. diaphana seem distinct taxa, while C. molesta var. crucifera is herein considered a synonym of

C. molesta.

Allied taxa

Some small Cocconeis species that have been recently described (Suzuki et al. 2001,2008,2012; Suzuki

& Tanaka 2006) from the Japanese coast, appear to share similarities with C. molesta and C. diaphana ,

particularly concerning their SV (on LM): e.g. C. churalis Hid. Suzuki, C. nagumoi Hid.Suzuki,

C. shikinensis Hid.Suzuki and C. baikalensis (Skvortzov & Meyer) Skvortzov. Nevertheless, these taxa

have no fascia on their RV and possess several features which allows them to be easily differentiated in

the SEM. Amongst the newly described taxa from Japan, Cocconeis tortilis Hid.Suzuki (Suzuki et al.

2014) has some morphological affinities with C. molesta , except for the RV fascia reaching the valve

margin and the SV sternum being larger than in C. molesta. The spiral aspect of Cocconeis tortilis may

be due to the ecology of the taxon (found as an epiphyte on Codium intricatum Okamura). Suzuki et al.

(2014: 223) also stated that Cocconeis molesta var. crucifera (synonym of C. molesta ) has no stauros,

but a wide fascia.

Conclusions

Our study stresses the importance of checking all possible original materials (especially types) in order to

make an improved species definition. Thus, the name Cocconeis molesta var. crucifera Grunow ex Cleve

could have been avoided. However, H. Van Heurck (1896), by examining Ktitzing’s original material

showed that there were no differences between the type of Cocconeis molesta and A. Grunow’s variety.

Our observations of these type materials corroborated H. Van Heurck’s supposition that C. molesta var.

crucifera is a synonym of C. molesta var. molesta. [Incidentally, it should be noted that C. molesta var.

crucifera Grunow was not validly published in 1880, since it was not accompanied by a description or

an illustration, but only by the mere mention of included subordinate taxa: cf. McNeill et al. (2012),

art. 36.1(d); only f. major Grunow and f. minor Van Heurck were illustrated and thus valid. The first

valid publication of var. crucifera is probably by Cleve (1895: 175). The same situation occurs for

C. amygdalina (in Van Heurck 1880-1885) since only f. minor Van Heurck and f. major Grunow were

illustrated; the first valid publication of the epithet amygdalina is also by Cleve (1895)].

Similarly, our examination of the original material of Cocconeis diaphana W.Sm. allowed us to point

out the differences between the two syntypes, which indeed belong to different taxa. Tectotypes have

been designated here for C. diaphana and C. dirupta.

From this study, three species have been recognized: Cocconeis molesta Kiitz., C. diaphana W.Sm.

and C. dirupta W.Greg. Cocconeis diaphana var. (3 is considered to be a synonym of C. dirupta and

C. molesta var. crucifera a synonym of C. molesta var. molesta.

Acknowledgments

We wish to pay tribute to our co-author Pierre Compere who was an excellent taxonomist and

enthusiastic collaborator with a great knowledge, particularly on the rules of botanical nomenclature.

We acknowledge Bart Van de Vijver (Botanic Garden Meise, Meise, Belgium) for allowing us to use

the Van Heurck slide collection facilities and for providing SEM photographs of the original material

of Cocconeis diaphana , Friedel Hinz (AWI, Bremerhaven, Germany) for her bibliographic help and

Peter Esteve (USR 3278, CRIOBE, Perpignan, France) for his help about iconography. Two anonymous

reviewers are greatly acknowledged for their constructive remarks. The Labex CORAIL, USR 3278

15

European Journal of Taxonomy 204: 1-18 (2016)

(CNRS-EPHE, CRIOBE) is acknowledged for funding the CORDIA program (COral Reef DIAtoms)

in the South Pacific.

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Manuscript received: 22 August 2015

Manuscript accepted: 4 February 2016

Published on: 14 June 2016

Topic editor: Koen Martens

Desk editor: Natacha Beau

Printed versions of all papers are also deposited in the libraries of the institutes that are members of the

EJT consortium: Museum national d’Histoire naturelle, Paris, France; Botanic Garden Meise, Belgium;

Royal Museum for Central Africa, Tervuren, Belgium; Natural History Museum, London, United

Kingdom; Royal Belgian Institute of Natural Sciences, Brussels, Belgium; Natural History Museum of

Denmark, Copenhagen, Denmark.

18