revision of the genus synedra ehrenb

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REVISION OF THE GENUS SYNEDRA EHRENB a

David M. Williams & Frank E. Round

b

a

Botany Department, British Museum (Natural History), Cromwell Road, London, SW7 5BD, United Kingdom b

Department of Botany, University of Bristol, Woodland Road, Bristol, BS8 1UG, United Kingdom Available online: 31 Oct 2011

To cite this article: David M. Williams & Frank E. Round (1986): REVISION OF THE GENUS SYNEDRA EHRENB, Diatom Research, 1:2, 313-339 To link to this article: http://dx.doi.org/10.1080/0269249X.1986.9704976

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Diatom Research (1986) Volume 1 ( 2 ) , 313-339

REVISION OF THE GENUS SYNEDRA EHRENB. David M. Williams Botany Department, British Museum (Natural History), Cromwell Road, London S W7 SBD, United Kingdom.

Frank E. Round Department of Botany, University of Bristol, Woodland Road, Bristol BS8 1 UG, United Kingdom.

A large number of species originally assigned to Synedru have been investigated mainly by scanning electron microscopy. Most are marine or brackish in distribution and structurally they differ considerably from Synedru as defined from the freshwater species and hence we have been able to recognise five new generic taxa - Catacombus, Hyalosynedru, Tabularia, Ctenophora and Neosynedru. The characters used for their distinction are discussed.

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INTRODUCTION

MATERIALS A N D METHODS

All previous classifications of Synedva Ehrenb. and Fvagilavia Lyngb. have expressed diversity in relation to colony formation. Where linear colonies are formed the species were assigned to Fragilaria whilst if the diatom is solitary or lives on mucilage pads in fanshaped or branched colonies, it was assigned to Synedva. Suggestions for improvement of this system have ranged from division of Synedra into subgenera (Kiitzing 1844; Frenguelli 1929) to the recent classification of all the common freshwater species in Fragilavia (Lange-Bertalot 1980). Neither solution has been successful and consideration has been given instead to generic separation (Round 1984). Colony formation is not always important in predicting the boundaries of taxa (Williams 1986). Once this criterion is disregarded Synedva can be defined with respect to other characters, but this leaves many species, previously classified in Synedra, without characterisation, and it leaves all the species of Fvagilaria in need of re-definition. We have examined many species formally allocated to Synedva and have assigned some to five new genera: Catacombas nov.gen., based on Synedva gaillonii (Bory) Ehrenb.; Hyalosynedva nov. gen., based on Synedva laevigata Grun. ; Tabulavia (Kiitz.) nov. stat., based on Synedva bavbatula Kiitz.; Ctenophova (Grun.) nov. stat., based on Synedva pulchella Ralfs ex Kiitz.; and Neosynedva nov.gen., based on Synedva pvovincialis Grun. During our separate investigations of many of the classical Synedva species we independently came to the conclusion that several generic taxa were involved. Whilst searching the literature we have discovered that many of our conclusions, derived from scanning electron microscopical observations, were foreshadowed in proposals by earlier light microscopist’s, stretching back to Kutzing (1844) and Grunow (1862). All too frequently their observations on live material were over-ridden by later considerations based on examination of cleaned material alone. The question of relationships between the new and the re-defined older genera has been deferred to a later paper.

The material that has been examined is noted in the species descriptions. Most of this material is located in the British Museum (Natural History) (BM). Scanning electron microscopy (SEM) was performed on a Hitachi S800 field emission electron microscope (BM) or a Philips 501 (Botany Department, Bristol University). The terminology used in this paper is principally that of Ross et al. (1979) with a few additions from recent proposals. In particular we have used the term sternum for the axial area (Mann 1978; Round 1979), ocellulimbus for the inset apical pore-field (Williams 1986) and closing plate for the valve areolae occlusions. We have also used the distinctions and nomenclature of von Stosch (1975) for girdle band identification, bearing in mind the additional notes in Mann (1982).

SYSTEMATIC OBSERVATIONS Catacombas Williams and Round, nov.gen. Valves linear, sometimes tapering towards the poles. Valve surface areolate, with regularly spaced, branched closing plates between transapical ribs. Areolation terminates a t the f a d m a n t l e junction and then continues again on the valve mantle. Mantle is turned at right angles to the valve face with each rib inter-connected at the junction. Valve constructed of two layers inter-connected by transapical ribs. Sternum distinct, central. Rimportulae at each pole, close to the polar pore field. The pore-field is of the ocellulimbus type and a few small spines overhang it. Girdle of four bands, all incomplete and ligulate. Valvocopula and copula non-areolate. Valvocopula attaching to the valve by a continuous, smooth lip. The two pleurae are areolate, with a single row of pores. Chromatophores are numerous, small and discoidal. Valvae lineares interdum ad polos angustatae. Pagina valvae areolata lamellis claudentibus ramosis inter costas transapicales regulatim dispositis. Areolatio in junctura superficiei palliique terminata tum in pallio valvae continuata. Pallium superficiale valvae ad angulum


Revision of Synedra

90" observa, quaque costa in junctura interconnexa. Structura valvae bistrata stratis costis transapicalibus interconnexis. Sternum distinctum centraleque quaque valva birimoportulata, rimoportulis polaribus prope agrum pori polaris ocellulimbularis sitis. Spinae parvae paucae lamellam pori imminentes. Cingulum ex quatuor redimiculis incompletis ligulatis constanti. Valvocopulae et copulae haud areolatae. Valvocopula valvae labio laevi continuo affixa. Pleurae duae areolatae serie pororum singulari ornatae. Chromatophora numerosa parva discoidea. Type species: Navicula gaillonii Bory (1827) p.564. Ehrenberg (1838) indicated that his species, S. balthica Ehrenb. was synonymous with S . gaillonii (Bory) Ehrenb. Previously he had transferred Navicula gaillonii to Synedra and this taxon should have become the type for the genus Synedra. However, 'Synedra' would be better conserved for species having the type of structure in Synedra ulna (Williams 1986, Ross in prep.) This means that S. gaillonii, if used as the type of a new genus, would need a new generic name. One other name which has been suggested for this taxon at subgeneric level, is Echinaria Kutz. Frenguelli (1929) proposed a subgeneric classification for Synedra, with Echinaria typified by S . gaillonii. However, when Echinaria was first proposed as a subgenus of Synedra by Kutzing (1844) he did not include S. gaillonii in his list of species. In addition the name Echinaria has been used twice before and is now conserved for a genus in the Gramineae, hence this name cannot be used at generic level for S. gaillonii. Thus a new name is proposed for this group of species. Two species, S. gaillonii and S . camtschatica Grun., have been assigned to this genus from the material that we have had available. Both species have previously been classified in Synedra but are distinct by virtue of three characters: (1) The appearance of the junction between valve face and mantle; (2) the nature of the chambering in the valve; and (3) the possession of areolate pleurae. Several other species of Synedra may belong here, e.g. Synedra tabulata var. obtusa Pant. (see p.90).

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Catacombas gaillonii (Bory) Williams and Round. comb.nov. Basionym: Navicula gaillonii Bory (1827), p.564. Synonyms: Synedra gaillonii (Bory) Ehrenb. (1830) p.129; S. baltica Ehrenb. (1832) p.87; S. capensis Grun. in Van Heurck (1881) p1.42, fig.1; S. gaillonii var. elongata H. & M. Perag; (1900) p.315, p1.80, fig.6; S. gaillonii var. gigantea Tempere & Peragallo (1909) p.156; Fragilaria gaillonii (Bory) Lange- Bertalot (1980) p.751. Type locality: ". . .Dieppe.. .[nous avons depuis retrouvk cette tspece en abondance sur les Ulves et les Achnantes des CBtes du Calvados]. . ." Type slide: MusCum d'Histoire Naturelle, Paris (not seen). Material studied: Shanklin, Isle of Wight, collected by Dr. Norkett. Wembury, S.Devon, epiphytic on Ectocarpus and Ceramium (F.E.R.). Valves linear, tapering slightly towards the poles (Fig. l ) , measuring 110-170 pm by 811 pm (according to Hustedt, 1932). The valve structure is complex, consisting of an inner and outer layer separated by transapical ribs (Figs 6,7). In the outer layer there is a series of areolae, each of which is occluded by a complex, branched closing plate supported from the adjacent transapical ribs (Figs. 2,3,9). This pattern is present on both valve face and mantle (Figs 4,9) but there is a distinct junction between these two parts of the valve (Figs 4,9). The inner layer of the valve is a smooth silica sheet perforated only below the valve face-mantle junction (Figs 6-8). Each pole has an ocellulimbus which extends around the polar mantle area (Figs 2-4,8,9). A single rimoportula occurs at each pole. It is somewhat proud from the valve interior and more stalked than is usual for araphid diatoms (Fig. 8). The girdle consists of four bands, all incomplete and ligulate (Fig. 4). They can be divided into a valvocopula, a copula and two pleurae (Fig. 4). The valvocopula and copula are non-areolate, with the valvocopula attached to the valve by a continuous, smooth lip, while each pleura has a single row of pores (Fig. 4). Reports in Karsten (1899) and Mereschkowsky (1902) indicate the


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chromatophores are discoid and dispersed randomly throughout the cells. It is apparently cosmopolitan in distribution, although most records to date are from the Mediterranean and Adriatic. Several varieties of this taxon have been described, all of which would repay further study. For instance, inspection of Kutzing’s type material of S. gaillonii var. minov Kutz. (BM 18312, Peru 218) reveals that his taxon is probably Tabulavia investiens (W.Sm.) Williams and Round (= Synedva investiens W. Sm.). Catacombas camtsckatica (Grun.) Williams and Round, comb.nov. Basionym: Synedva camtsckatica Grunow (1862) p.404, p1.8, fig. 6. Synonyms: ?S. karntsckatica var. minov Grun. in Cleve & Grunow (1880) p.106; ?S. kamtsckatica var. intevmedia Grun. in Cleve & Grunow (1880) p.106, p1.6, fig.111; ?S. kamtsckatica var. kjellmani Grun. in Cleve & Grunow (1880) p.106, $6, fig.10; ?S. kamtsckatica var. connectens Grun. in Cleve & Grunow (1880) p.106; ?S. kamtsckatica var. finnmavckia Grun. in Cleve & Grunow (1880) p. 106, p1.6, fig. 112; Fvagilavia camtsckatica (Grun.) Poulin, Berard-Therriault & Cardinal (1984) p.351. Type locality: “Habitat in mari camtschatico. ” Type slide: Naturhistorisches Museum Wein (not seen). Material studied: “Les Escoumains”, Co. Duplessis, Quebec. 20kms east of the Saguenay fjord in the maritime part of the St.Lawrence Estuary. 10th July 1979. Provided by Dr. A. Cardinal. BM 12767. Cleve and Moller slide no.23. Finmarken, Maaso. Coll. R.F. Kjellman.

Figs 1-9. Catacombas gaillortii. Figs 1-3, 5-8 Shanklin, Isle o f Wight, collected by Dr. Norkett. Figs 4-9 Wembury, FER Fig.1. External view of whole valve, Bar=hO pm. Figs 2 & 3. Detail of external view of ocellulimbus and adjacent rimoportula, cribra can be clearly seen, Bar=3.0 pm. Fig.4. Frustule with mature epicingulum. Four bands arc present, Bar=8 pm Fig.5. Detail of outer valve wall

Probably type material for the Cleve and Grunow varieties above. As C . gaiflonii but measuring 120-230 pm by 7-8 p m in our specimens - for details see Figs 10-16. Towards the centre of the valve only thickened wall remains (Figs 10,14); in the light microscope this gives a brighter outline and is a distinctive feature for identification of this species (Fig. 10). A single rimoportula occurs at each pole but it is not so well developed as that in C. gaillonii (Fig.13). Girdle as in C. gaillonii. This species is so distinctive in the light microscope that it is unlikely to be confused with any other. Several varieties have been identified but most authors consider these as minor variations in size and shape and not indicative of separate taxa. The apparent doubling of the striae count in S. kamtsckatica var. finnmavckia is due to focusing through the double valve layer and resolving the detail of the underlying striae. Hyalosynedva Williams and Round, nov. gen. Valves linear, tending to be capitate, with a distinctive narrow sternum. Striae very dense with small areolae extending across the valve face to the narrow sternum and opening into transapical chambers. Closing plates complex, their supporting struts aligned in the transapical plane. The mantle edge is wide, distinct and swollen. Ocellulimbus with the pore plate sunk into the polar valve mantle. A few spines overhang the pore plate. Internally the valve is featureless except for the small openings between the valve face and mantle. Rimoportulae present at each pole adjacent to the pore field. Girdle consisting of three bands: a non-arcolate valvocopula, copula and single pleura each with a row of pores in the pars media.

illustrating cribra, Bar=3.0 p m . Fig.6. Broken cross-section o f valve revealing two layers. The highly silicified sternum and struts o f the cribra can be seen clearly, Bar=3.0 p i . Fig.7. Detail of above, Bar=1.36 pni. Fig.8. Internal view of polar aspect of valve, showing ocellulimbus and stalked rimoportula, Bar=2.3 pm. Fig.Y. Detail of external view of ocellulimbus. Note the non-occluded pores nearest the pore-field and the few spines above the plate. Bar=5 pm.


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& F.

E. Round

Valvae a forma lineare ad formam capitatum sternum distinctum praeditae. Striae densissimae areolis parvis trans superificies valvae ad sternum angustatum extenditibus et in loculus transapicales ingredientibus. Lamellae claudentes complexae tigillis fulcrantibus in superificie transapicales positis. Ocellulimbus spinis paucis im pendentibus praeditus. Valvae interior sine proprietatibus praeter foramina parva inter valvae superficies et pallium posita. Rimoportulae in polo quoque juxta polar agrum pori positae. Cingulum trivittatum ex haud areolata et copula et pleura singulari constans, vitta quaque serie pororum in parte media inserta ornata. Type species: Synedra laevigata Grunow (1877) p.166, p1.193, fig.3. The detailed structure of the valve and girdle is extremely difficult to observe in the LM, most observers therefore describe this species as being devoid of structure. However, SEM reveals a complex and elaborate valve. The obscurity of the striae, in LM, is due to the narrow and dense structure which in turn serves to highlight the central stern m The openings of the chambers into 7 . t k valve of Hyalosynedra laevigata are situated in the corner of the mantle/face and are obscured by the upper rim of the mantle. Initially, Catacombas and Hyalosynedra were considered to be synonymous but closer inspection revealed several distinct characters for Hyalosynedra, most noticeably the uninterrupted striae at the valve face/mantle junction, the construction of the valve chambers and the three band cingulum. All these characters are difficult to observe in the LM. It is possible to discern the chambered structure in Catacombas in the LM and use this feature for identification purposes. In Hyalosynedra (in the LM), one has to rely on the density of the striae, the thin sternum and I

Figs 10-16. Catacornbas carntschatica. Fig.10. In mare arcticum, H.L. Smith 561. Figs 11-16 Co. Duplessis, Quebec, Dr. A. Cardinal.

Fig. 10. LM. Specimen length 150 pm. Figs 11 & 12. External view illustrating ocellulimbus and rimoportulae, Bar=S.O pm. Fig. 13. Internal polar view illustrating ocellulimbus and rimoportula,

the plain valve apices (see illustrations in Hustedt, 1932). Having established these distinctions, it is possible to deduce that Synedra distinguenda Hust. is a species of this genus and Synedra platensis (Freng.) Freng. is a species of Catacombas. In the original description of Synedra platensis, Frenguelli indicates that his species is identical to specimens on slide no. 354 of Tempkre & Peragallo (1909). However, without material for SEM we are reluctant to make the transfer on the basis of cleaned LM material only. Records of H . laevigata from the tropics might refer to Synedra platensis. Hyalosynedra laevigata (Grun.) Williams and Round, nov.comb.

Basionym: Synedra laevigata Grunow (1877) p.166, pl.193, fig. 3. Synonym: Fragilavia laevigata (Grun.) LangeBertalot (1980) p. 752. Type locality: " ...I have seen this diatom from various localities (Honduras, Mauritius, Samoa Islands). . ." Grunow (1877), p.166. Type: Naturhistorisches Museum Wein (not seen). Material studied: Epiphytes on Seagrass. Canigaran beach, north of Puerto Princesa City, Philippines. Nov. 30th 1978. T.B.B. Paddock. North and northwest side of Island on coral reef. Collected on the Philippine Isles at Station no. 9. P.S. Moreland [sometime between 24th February 1973 and 10th March 19731. Valves linear with rounded or tapered poles (Figs 17,18), measuring 100-240 pm by 5-7 pm in our specimens. Striae with evenly spaced areolae extending in unbroken rows to the mantle margin (Figs 19,23). There is no abrupt angle at the junction of the face and mantle but merely a gentle curve towards the

Bar=2.7 pm. Fig.14. Internal view of central thickened area, Bar=6.0 pm. Fig.15. External polar view showing complete epicingulum. Note also ocellulimbus, closing plate structure and unoccluded pores nearest ocellulimbus, Bar=2.5 pm. Fig. 16. Broken cross-section of valve showing double layer, Bar=2.0 pm.


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edge of the valve (Figs 19,23). The striation stops short of the mantle leaving a clear space (Fig.20). Each areola is occluded by a small closing plate with struts orientated in the transapical plane (Fig. 19; Fig.23 has the closing plate missing). A central sternum is present externally extending the full length of the valve (Figs 19,23). At the poles a few unoccluded pores occur (Figs 19,21). There are usually between three to nine rows of evenly distributed poroids in the ocellulimbus; 3-4 short spines overhanging the uppermost portion of the pore-field (Fig. 19). Internally, the valve is smooth and structureless (Figs 1720,22), except towards the junction ofthe face and mantle, where there is a series of apertures passing into the valve chambers (Figs 17-20, 22; Fig.23 arrow indicates opening). A rimoportula is situated at each pole close to the ocellulimbus (Figs 17-20). In some respects the rimoportula is similar to that of Thalassionema Grun. ex H u t . in that the pairs of lips have an inner and outer component, with the outer component curved around the inner (Figs 17-20; see Hallegraeff 1986). The cingulum consists of only three bands: a valvocopula, a copula and a pleura. They form a series of alternating, incomplete, ligulate bands (Fig.21). The valvocopula is plain, underlapping the valve and connecting to the valve edge by a continuous, smooth flap (Fig.19). The copula is identical in structure, but shorter; the pleura has a large ligula to compensate for the reduced size of the copula (Fig.21). The pleura is much narrower and has a single row of poroids (Fig. 21). Tabularia (Kiitz.) Williams and Round, nov.stat. Basionym: Subgenus Tabularia Kiitzing (1844) p.67. Figs 17-23. Hyalosynedra laevigata. Figs 17,18 2022 Philippines, Canigaran Beach, T. B.B. Paddock. Figs 19,23 Philippines, P. S. Moreland. Figs 17 & 18. Internal polar views, edge of ocellulimbus is just visible along with the unequal rimoportula, Bar=4.3 prn. Fig. 19. Separated frustule with both inner and outer parts of valves illustrated. Three bands in cingulum, Bar=1.76 pm. Fig.20. Internal view of valve with

Valves elongate, usually linear, rarely capitate. Striae more or less parallel, separated internally by distinct ribs. Areolae cribrate, extending from valve face to mantle or separated into discrete valve face and valve mantle series. Areolae biseriate or separated by conspicuous bars. The inner edge of the mantle forms a lip from which ribs extend towards the sternum. Ocellulimbus small, with few poroids per plate. A single rimoportula is situated close to one ocellulimbus, or slightly to one side, and set obliquely. The cingulum consists of a few open, ligulate bands. The valvocopula is plain and attaches to the valve by a stepped pars interior folded to coincide with the ribs of the valve; it is not perforated. Copulae and pleurae with a single central to sub-central row of poroids. Type species: Synedra barbatula Kiitzing (1844) p.68, pl.15, fig. 4. Kiitzing (1844) used Tabularia as a subgenus within Synedra. His description was short and concentrated on the living condition: “Stipiti horizontaliter crescenti affixae, tabulatium disruptae. He included 11 species and all may be members of Tabularia as now conceived, viz. S. familiaris, S. arcus, S . barbatula, S . fasciculata, S . tabulata and S. affinis. It was decided to typify this genus with S. barbatula Kiitz., since type material was available and has been studied by us using LM and SEM. Furthermore, although Tabularia is a variable genus, S. barbatula is one of the most representative species, taking into account the morphological groups indicated below. T .fasciculata (=Synedra fasciculata (Ag.) Kiitz.) has such a confusing taxonomy that it is not suitable for the typification of a genus. Although there are three variants of valve structure in the genus, we have not accorded ”

I

openings and smooth internal surface, Bar=2.5 pm. Fig.21. Detail of cingulum, pores in pleura just visible. Note also the unoccluded series of pores just before the ocellulimbus, Bar=2.0 pm. Fig.22. Partly fractured valve showing double layer construction, Bar=l.2pm. Fig.23. Obliquely fractured valve cut across the chambers of the valve. In the corners can be seen the internal openings, arrowed, Bar=3.8 pm.


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them taxonomic status since there are many unifying features. However, we fully appreciate that subsequent investigations of these taxa may reveal further divisions. (1) The first type encompasses a group of species having biseriate striae with simple closing plates, a single rimoportula, probably several copulae in the cingulum and generally measuring around 20-50 pm along the apical axis. Examples are Tabularia barbatula (Kutz.) Williams and Round nov. comb. and T . parva (Kutz.) Williams and Round, nov.comb. This morphology is so far restricted to species present in European waters. However, this apparent narrow distribution may be due to difficulties encountered in identifying these species using LM only. (2) The second type has cribra with heavily silicified cross-members and several copulae. An example we have studied is T . investiens (W.Sm.) Williams and Round nov.comb. (see also Holmes and Croll, 1984). (3) The third type has the complex, cribrate closing plate exemplified in T.fasciculata (Ag.) Williams and Round, nov. comb. and its allies (see also Lange-Bertalot, 1980). All the above groups share distinctive characters of the girdle, a branched closing plate and usually a single rimoportula. -There is some confusion as to the morphology of the chromatophores. Notwithstanding the difficulties of current nomenclature, many reports of S. afinis (possibly equal to T . fasciculata) and its varieties are misleading. Synedva affinis has been reported with several oval plates (Karsten, 1899; and Gemeinhardt, 1926); Synedra afinis var. parva, S. afinis var. fasciculata and Synedra fasciculata as having two plates (Pfitzer 1871; Mereschkowsky 1902); and finally Synedra afinis var. gracilis and Synedra gracilis as having 8-10 small plates (Pfitzer 1871; and Mereschkowsky 1902). We have made no attempt to analyse the seemingly disparate observations here but will

do so in a later paper (Williams and Round, in prep.). All species included in this genus are in need of revision and some taxa placed as infraspecific entities of Tabularia may need to be located elsewhere. An example is Synedra tabulata var. obtusa. This was illustrated by Gemeinhardt (1926) as having many chromatophores and in Hustedt (1932) appears with distinct marginal striae. These observations suggest to us a species of Catacombas rather than Tabularia.

Figs 24-32. Kutzing.

Fig.28. Detail of internal view of sternum, ribs and mantle, Bar=0.86 pm. Fig.29. Girdle view of frustulc showing different bands, Bar=3.0 pm. Fig.30. Detail of external view of biseriate striae showing closing plate struts and sternum, Bar=1.2 pm. Figs 31 & 32. Detail of valvocopula showing crenulated pars interior, Bar=1.36 prn.

Fig.24.

Tabularia barbatula. Type material,

Internal

view

of

whole

valve,

Bar=l2.0 pm. Figs 25 & 26. Detail of valve poles note rimoportula in Fig.26 only, Bar=2.0 pm. Fig.27. Detail of central areolation, Bar=l.2 pm.

Group 1 Tabularia barbatula (Kutz.) Williams and Round, nov. comb. Basionym: Synedra barbatula Kutzing (1844) p.68, p1.15, fig.4. Synonym: Synedra gracilis Kutzing (1844) p.64, p1.14, 11, b; p1.15, VIII, 1 non p1.3, fig. 14. Type locality: “An Conferven auf Helgoland in Meere.” Type slide: BM 18314 Valves linear-elliptical, tapering towards each pole, measuring 20-28 pm by 4-5 pm (Figs 24-26). Striae fine, 15-18 in 10 pm (all measurements taken from Kutzing’s specimens.) The ribs are opposite, evenly spaced and parallel thoughout the length of the valve (Figs 24-28,30). Internally the striae continue close to the edge of the valve margin which is thickened (Fig.28). The sternum is narrow and of uniform width and all elements of the valve are interconnected with no further differentiation (Figs 24-28,30). The striae are biseriate. The circular, opposite areolae are covered by cribra suspended between 5-8 irregular struts (Figs 27,28,30). A singlc rimoportula is situated at a pole, close to the occllulimbus (Figs 24,26). The ocellulimbus is composed of 6-8 rows of 7 poroids, and is


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enclosed by a small rim (Figs 25,26,29). The girdle has four bands (Fig.29) with the valvocopula a non-areolate open band with an interior flap which adheres to the valve mantle margin (Figs 31,32). The pars interior is slightly crenulated to fit over the valve ribs (Figs 31,32). The copulae are open ligulate bands with a single irregular row of poroids more or less along the centre of the band (Fig.29; poroids arrowed). The pleura is not easily recognised and is often missing from cleaned valves. When present it can be distinguished by its relatively smaller size and the depth of the ligula (Fig.29). Synedva gvacilis Kiitz. has become entangled within the nomenclature of S . barbatula. In the protologue to S. gvacilir, Kiitzing (1844) gives two localities: “An Seealgen im mittellandischen Meere bei Genua!” and “in der Nordsee!” Cells from the first locality, illustrated by Kiitzing as Taf.3, fig. XIV is considered a separate taxon by some authors. Those from the second locality, illustrated by Kiitzing as Taf.14, IIb and Taf.15, VIII 1 (BM 18199) are considered to be synonymous with S. barbatula. S. gracilis has been used in several different senses by different authors including Brun (1880), Grunow in Cleve & Grunow (1880), W. Smith (1856) and Lagerstedt (1876). All of these authors appear to be dealing with specimens that are probably Tabulavia species, with the exception of Smith, whose specimens are Ctenophova pulrhella (Ralfs ex Kiitz.) Williams and Round, nov.comb. Tabulavia pavva (Kiitz.) Williams and Round, nov.comb.

Basionym: Synedva pavva Kiitzing (1849) p.46. Synonym: Synedva pavvula Kiitzing (1844) p.67, p1.15, fig.IV, non Synedva pavvula Kiitzing (1844) p.64, pl. 14, fig.1; S. tabulata var. pavva (Kiitz.) Hustedt (1932) p.219; Fvagilavia tabulata var. pavva (Kiitz.) LangeBertalot (1980) p.750. Figs 33-38. Tabulavia pavva. Figs 33-37 Hannover, Jamaica, Dr. A.C. Podzorski. Fig.38. BM 18359. Type slide. Fig.33. Internal view of whole valve, Bar=lO pm. Figs 34 & 35. Detail of valve poles

Type locality: “An Callitkamnion Borrevi bei Trieste. Type slide: B M 18359 (Fig.38). Material studied: Hannover, Orange River Estuary; Scrapings from rocks, Jamaica. A. C. Podzorski, 7th Oct. 1978. Valves linear-elliptical, tapering towards each pole and measuring 20-35 pm by 4-6 p m (Fig.33). The ribs evenly spaced and parallel along the length of the valve (Figs 33-35). Internally the striae taper towards the sternum and continue almost to the edge of the valve. The sternum is wide centrally but tapers towards the apices (Figs 33-35). All elements are interconnected with no further differentiation (Figs 33-35). Striae biseriate, the areolae being opposite and covered by cribra suspended between 5-8 struts (Fig.36). A single rimoportula is situated at a pole close to the ocellulimbus (Figs 33,35). The girdle is only partially known; the valvocopula is an open, non-areolate band with an interior flap which underlaps the valve mantle margin (Fig.37). The copulae are all open bands with a single row of poroids on the pars interior (Fig.37). This species has previously been considered as part of the T . fasciculata complex. SEM investigations reveal that it is more closely related to those species with the biseriate type of morphology. ”

Group 2 Tabulavia investiens (W.Sm.) Williams and Round, nov.comb. Basionym: Synedva investiens W. Smith (1856), p.98. Synonym: Fvagilavia investiens (W.Sm.) A. Cleve-Euler (1953), p. 44, fig.354. Type locality: “Marine, thickly covering an Ectocavpus. Kirkaldy, Fifeshire, March, 1854. Dr. Greville.” Type slides: BM 23798-23800 (and BM 1133). note rimoportula in Fig.35 only, Bar=2.3 pm. Fig.36. Detail of biseriate striae showing closing plate construction, Bar=0.5 pm. Fig.37. Girdle of partial epicingulum; note also view ocellulimbus, Bar=1.76 pm. Fig.38. LM of type specimen, valve length 30 pm.


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Material studied: Heard Island, material from Jan Mercer. Epiphytic material from Wembury and Plymouth, South Devon collected by F.E. Round. Valves linear-elliptical, tapering towards rounded poles, measuring 25-35 pm by 24 pm (Figs 39,41). Hustedt (1932) gives the wider range, 15-50 pm. The ribs are evenly spaced and parallel, extending the length of the valve (Figs 39,42,43, 45). Internally the striae continue up to the edge of the valve (Figs 40,41). The sternum is distinctive and rather wide and can occupy at least one-third of the valve surface (Figs 39,42, 43,45). The striae are parallel with prominent cross-bars set in the depressions between the transapical ribs, delimiting longitudinally elongate areolae containing cribra (Figs 39-43). A single rimoportula is situated at a pole adjacent to the ocellulimbus (Figs 39,40). The ocellulimbus is composed of 6-8 rows of 7 poroids, and is enclosed by a small rim (Figs 40,41, 43). The girdle has 6-8 bands (Fig.45 shows 7). The valvocopula is a non-areolate open band with an interior slightly crenulate flap (Fig.44, arrowed). The copulae are open ligulate bands, each with a single row of irregularly placed poroids more or less at the pars media (Figs 44,45). Holmes & Croll (1984) illustrated this species and suggested that their specimens had only between two to four bands in the cingulum - further material should be investigated to check variability in girdle structure. The final 2 bands in the epicingulum are possibly better interpreted as pleurae as the ligulae differ in size (Fig.45). A marine species, predominantly attached by one pole, although short, linear colonies have been reported (Cleve-Euler 1953). Group 3 Tabularia fasciculata (Ag.) Williams and Round, nov.comb. Basionym: Diatoma farciculatum Agardh (1812), p.35. Figs 39-45. Tabularia investiens. Fig.39 Wembury, Fig.45 Plymouth, F. E. Round. Figs 4044 Heard Island, Dr. J. Mercer. of whole valve, Fig.39. Internal view Bar=5 pm. Figs 40 & 41. Detail of valve poles; rimoportula in pole of Fig.40 only and external

Synonyms: ? Exilaria fasciculata Greville (1824) p1.16, figs 1-3, vo1.5, pl.298, fig.3; D i a t o m a tabulaturn Agardh (1832) p.50; Synedra affinis Kutzing (1844), p.68, pl. 15, fig.11, XI, p1.29, fig.I,5; S . fasciculata (Ag.) Kutzing (1844), p.68, pl.15, fig. V, p1.16, fig.VI, figs 1-3; S. tabulata (Ag.) Kutzing (1844), p.86, pl. 15, fig.X, 1-3; S . affinir var. fasciculata (Ag.) Grunow in Van Heurck (1881), p1.41, fig.15; S . affinis var. tabulata (Ag.) Juhlin-Dannfelt (1882), p.43, p1.3, fig.27; S . tabulata var. acuminata (Grun.) Hustedt (1932), p.219, fig.710 e,f; S . tabulata var. fasciculata (Ag.) Hustedt (1932), p.218, fig.710, i-1; S . fasciculata var. truncata (Grev.) Patrick in Patrick & Reimer (1966), p.142, p1.5, fig.16. Type locality: “In plantis marinis ad Bastad hieme. Type slide: Ag.-Herb. 4185a Bastad (See Patrick and Reimer, 1966, p1.5, fig.17. Isotype.) Not seen. Material studied: Heard Island, J. Mercer. “Les Escoumains”, Co. Duplessis, Quebec. 20kms east of the Saguenay fjord in the maritime part of the St.Lawrence Estuary. 10thJuly 1979. Provided by Dr. A. Cardinal. There is considerable confusion over the identity and nomenclature of this species; several taxa are probably involved. It is such an important species that it would be unwise to omit it simply because of species ambiguities. We have chosen to follow the most recent discussion in Archibald (1983), adopting his synonymy. Valves linear, slightly tapering at the apices (Fig.46). The sternum is distinctive and usually broad, interconnecting with the ribs, which are parallel except at the poles, where they radiate slightly (Figs 46-48). In crosssection the ribs can be seen to interconnect the valve margin with the sternum (Fig.50). The ribs are widely spaced and between them are complex closing plates (Figs 46-52). In our specimens there are 6-7 small, evenly spaced struts on either side of the ribs and these ”

view of ocellulimbus in Fig. 41, Bar=1.20 p m . Figs 42 & 43. Detail of external view of valve showing areolae construction, Bar=1.20 pm and 1.76 pm respectively. Fig.44. Detail of polar view of epicingulum. Valvocopula pars interior arrowed, Bar=3.0 pm. Fig.45. Frustule with a probably complete epicingulum, Bar=5 pm.


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support a cribrum (Figs 46-52). The striae pattern is present on the mantle but with a definite border between valve face and mantle (Figs 49-52). The valve mantle has scattered plaques along its edges (Fig.49; arrowed). Externally, the valve areolae do not reach to the poles but finish just short with a single row of unoccluded pores (Fig.52). The ocellulimbus is sunk into the polar valve mantle with a slightly thickened rim (Fig.52) and contains 9-15 rows of 6-8 poroids (Fig.52). In some of our specimens there appears to be a single rimoportula at each pole, closely associated with the pore field (Figs 46,47); in other specimens there is a single rimoportula at one pole. The phylogenetic significance of this will be discussed in a later paper (Williams & Round, in prep.). The cingulum is of a simple openbanded, ligulate type with three bands (Figs 51,52). The valvocopula is plain and has a simple continuous edge slightly indented to accomodate the valve ribs (Figs 51,52). The valve mantle has an internal margin to which the valvocopula attaches (Fig.50). The copula has a single row of poroids situated slightly off-centre and towards the pars interior - they are obscured by other bands in situ. The pleura is very much thinner and lacks pars interior structure along the length of the band; it has a larger ligula than that of the copula and an indented pars interior at the apex (Fig.51, arrowed; Fig.52). Some of the taxa associated with T . fasciculata may probably have to be redistributed into other marine genera or be treated as distinct species of Tabulavia. Further confusion remains between taxa identified in the literature as Synedva a f j n i s and S . tabulata and their associated varieties. All species require close examination and we would not be at all surprised if other genera and many more species were discovered in this complex. Archibald (1983) has made a detailed revision of T . fasciculata based on his South African

specimens. The closing plates in particular were very variable, with specimens having from 4-10 struts and lacking the branching component in some cases (Archibald, 1983, p1.33, figs 561-3). In other specimens there were as few as 2-3 struts with no branched plate and the central interconnecting bar was more silicified than the remaining plate structure (p1.33, figs 562-3). Archibald considered this sufficient enough evidence to recognise a separate taxon, Synedra fasciculata f. densistviata. An alternative conclusion, based on the presence of cross-bars, is a close relationship with T . investiens rather than T .fasciculata. In the recent revision of Fvagilavia by Lange-Bertalot (1980) he illustrated several specimens in different stages of errosion and with closing plates having 3-5 struts. However, he also included SEM’s of type specimens of Fvagilavia fonticola Hust. in which there was a closing plate with 11 struts uniformly arranged around the longitudinal valve bars. In addition, the branched arrangment inside the plate was different (Taf.16, figs 277,278). No other details of the structure were illustrated, making it difficult to compare these specimens with ours. We do not feel a colonial form of Tabulavia is impossible but reserve judgement in this case as there are certain similarities between Fvagilavia fonticola and species of Stauvosiva Ehrenb. (Williams & Round, in prep.). Frenguelli (1942) made similar comments on specimens of Fvagilavia fonticola from South America. Finally, Cholnoky (1963) described a species of Fvagilavia, F . giesekii Choln., from brackish waters of South Africa which is similar to F . fonticola. We have examined specimens of F . giesekii in the LM from type material (BM Cholnoky N.G.4) and again it is difficult to be certain of this taxon. Cholnoky, in the legend to the figure of this species indicates “Fvagilavia (Synedva?)”.

Figs 46-52. Tabularia fasciculata. Figs 46-50 Co. Duplessis, Quebec, Dr. A. Cardinal. Figs 51 & 52 Heard Island, Dr. J. Mercer.

m. Fig.49. External view of valve areolation; mantle plaques arrowed, Bar=l.O pm. Fig.50. Broken part of valve showing cribra structure and mantle structure, Bar=1.2pm. Figs 51 & 52. Dismantled frustule showing the three bands. In Fig.51 the small pleura is arrowed. Fig.52 shows the large ligula of the pleura. Note also the rimoportula, Bar=3.0 pm and 2.5 pm respectively.

Fig.46. Internal view of whole valve, Bar=20 pm. Fig.47. Detail of pole containing single, oblique rimoportula, Bar= 1.5 pm. Fig.48. Internal view of sternum and striation, Bar=1.5 p


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Ctenophora (Grun.) Williams and Round, nov.stat. Basionym: Subgenus Ctenophova Grunow (1862) p.385. Valves linear to lanceolate, with weakly capitate or rounded poles, uniseriate striae and branched closing plate. There is a prominent, plain central area with a heavily silicified border and “striae-like’’ indentations are present internally. A single rimoportula is present at each pole, usually positioned transapically but on occasions obliquely. The rimoportulae are diagonally placed relative to the sternum. An ocellulimbus is present at each pole. The girdle is incompletely known. The valvocopula is a non-areolate open band; the pars interior is crenulated, corresponding to the striae and additionally has a larger central modification to fit the central area of the valve. At either pole the bands taper towards the valve. Type species: Synedva pulchella Ralfs ex Kiitzing (1844), p.68, p1.29, fig.87. Ctenophora has been proposed to accommodate a single species. Grunow (1862) originally used the name Ctenophora for a “Gruppe” in his subdivisions of Synedva. In this group he included several species that all appeared to have a distinct central area. Later, von Schonfeldt (1907) used the same subdivisions but did not place all of Grunow’s species in them. C . pulchella appeared in both classifications, and when Frenguelli (1929) used Ctenophova for a subgenus of Synedva he typified it with Ctenophova pulchella. In Grunow’s description of Synedva pulchella, he refers to the name Ctenophova pulchella BrCb. but it seems this combination was never validly published. Von Schonfeldt (1907) referred to this species as a Synedva within the sub-group Ctenophova Grun. However, on p.248 of this work in the “Register der Gattungen und Arten”, he indexed the species under the name Ctenophova pulchella, but Figs 53-61. Ctenopkora pulckella. Figs 53,54 Bucket Rock, T.B.B. Paddock and P.A. Sims. Figs 55,58,60,61 Type material ex Kutzing. Fig.56 Mull, Fig.57 Wembury, Fig.59 Mull, F.E.Round. Fig.53. External view of whole valve, Bar=lO pm. Fig.54. Internal view of whole valve, Bar=lO pm. Fig.55. Detail of internal view of

referred to it in the description of his illustration as Synedva. Again this cannot be considered a valid combination. Although at present we have only included one species, the large and complex synonymy for C . pulchella suggests that several new taxa will be uncovered when a more critical study is completed. Ctenophova pulchella (Ralfs ex Kiitz.) Williams and Round, nov. comb. Basionym: Synedva pulchella Ralfs ex Kiitzing (1844), p.68, pl. 29, fig.87. Synonyms: S . aciculavis W.Smith (1853), p.70, non S . aciculavir Kiitzing (1844), p.63; S . rmithii Ralfs in Pritchard (1861), p.756. Type locality: “An Conferven in England. Original exemplare wurden mir von dem Hrn. Berkeley mitgetheilt.” Type slide: BM 18310. Material studied: Epiphytes on Aspeuoccus. Bucket Rock, Berwick-upon-Tweed. T.B.B.Paddock and P.A.Sims, 23, 26th Aug. 1972. Epiphytic on Cevamium from Wembury, S.Devon and in cultures from epiphytes collected in Plymouth Sound. F.E. Round. Valves linear to lanceolate, with weakly capitate or rounded poles, 30-150 pm by 58 pm (Figs 53,54). Striae relatively dense, up to 15 in 10 pm, and conspicuously punctate in the LM (Figs 53-59). The sternum extends the length of the valve. The central area is distinct in the LM, since the thicker silicification around it gives a brighter appearance (Figs 5356); Faint in-filled striae are visible here (Fig.55). In the SEM the valve is seen to have uniseriate striae (Figs 53-59). The areolae are occluded by simple porate plates (Figs 56,57; also Granetti, 1984, p1.10, fig.4). A single ‘rimoportula is present at each pole, usually situated transapically, but in some valves obliquely, and they are diagonal to each other (Figs 54,58,59). An ocellulimbus is present a t central area, Bar=3.0 pm. Fig.56. Detail of central area and cribra, Bar=5 pm. Fig.57. Detail of cribra, Bar=5 pm. Fig.58. Internal view of pole with rimoportula, Bar=S.O pm. Fig.59. Internal view of ocellulimbus and oblique rimoportula, Bar=1.5 pm. Figs 60 & 61. Details of valvocopula, Fig.60 shows central area attachment and Fig.61 shows closed end of band, Bar=3.0 pm.


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each pole (Fig.59). The girdle is incompletely known. The valvocopula is a non-areolate open band with a crenulated edge on the pars interior corresponding to the striae, with a larger space corresponding to the central area (Figs 60,61). At either pole the bands taper towards the valve (Fig.61). Reports of the chromatophores of Ctenophora pulchella state that two plates are present. C. pulchella is cosmopolitan and common in brackish water. It is an attached species usually forming small, branched colonies with each frustule attached to the substrate at only one pole. Neosynedra Williams and Round, nov.gen.

Valves elongate, with a slightly expanded portion at the centre and slightly capitate to rounded poles. Sternum conspicuous and well developed. Areolation of evenly spaced, uniseriate rows continuing down the valve mantle; areolae occluded by cribra on the outer surface. Apical pore fields extend onto the valve face and consist of elongate pores, separated laterally by long bars; there are intermittently spaced shorter cross-pieces which link the bars. A rimoportula is situated adjacent to the apical pore-field. Girdle of up to six bands, all incomplete and ligulate. Each band has two separate rows of areolation, one on the pars interior and one on the pars exterior; each pore is closed by a cribrum. There is no distinction between bands except for a decrease in width in the abvalvar direction. The valvocopula is identical to the other bands except that the pars interior has a simple lip to attach to the valve. Valvae elongatae in centrale leviter expansae in polis leviter capitatae vel rotundatae. Sternum conspicuum bene evolutum. Areolatio aequaliter dispostita in pallium uniseriate deorsum extensa; areolae in pagina exteriori cribris occultae. Agri polorum apicali in superficiem Figs 62-67. Neosynedra provincialis. Fig.62 Majorca, F.E.Round. Figs 63-67. Bohuslan, Dr. M. Kuylenstierna.

of whole valve, Fig.62. Internal view Bar=lO pm. Fig.63. Detail of striae and pore-field, note also external aperture of rimoportula, Bar=l.O pm. Fig.64. Polar view of cingulum, note

valvae extendententes, poros elongatos transtris longis lateraliter segregatos, formantes. Rimoportula juxta agrum polorum apicalem. Cingulum sexvittatum vittis omnibus in completis ligulatis. Vittae quaque seriebus duabus areolarum separatis ornata, cujuoque areolae una serie praeditis parte interiori et parte exteriori; polo quoque areolae per cribrum clauso. Vittae inter s e x haud distinctae praeter contractionem latitudinalem in directione exabvalvari. Valvocopula vittis aliis simillima praeter partem interiorem labio simplici in valva affixo. Type species: Synedra provincialis Grunow (1877), p.187. This genus is characterised by the compound, slit like apical pore-fields which resembles those of Cyclophora Castr., except that in Cyclophora the pore-field is divided into two parts by a plain central region (Navarro 1982). There are certain similarities with Protoraphis Simonsen in pore-field structure and girdle structure (Gibson 1979). Neosynedra provincialis (Grun.) Williams and Round, nov.comb. Basionym: Synedva pvovincialis Grunow (1877), p.166, p1.193, fig.6. Type locality: “Habitat in mari Meditteraneo ad oras Galliae prope Cette (Leg L. Lindig)”. Type slide: The pages of Grunow’s diary indicate two slides that Grunow used for the description. Both of these slides were made from identical material. Grunow slide no. 1039 (Cette leg. Lindig no.100), Grunow slide no. 1040 (Cette leg. Lindig no. 101). These slides are located at Naturhistorische Museum Wien. Grunow slide no.1039 is designated as lectotype. Material studied: Bohuslan, Roro, August 1981, D r . M. Kuylenstierna. Epiphytic on seaweeds from Majorca. F.E. Round.

identical bands and the pars interior of- the valvocopula, arrowed, Bar=2.3 pm. Fig.65. Internal view of pore-field and rimoportula, Bar=1.2 pm. Fig.66. Detail of cribra and sternum, Bar=l.O pm. Fig.67. Internal view of cribra struts taken from a central portion of valve, Bar=O.75 pm.


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Valves elongate, slightly expanded at the centre and with slightly capitate to rounded poles (Fig.62), 65-110 pm by 4-7 p m (according to Hustedt, 1932). The sternum is conspicuous and well developed (Figs 62,66); The areolae are evenly spaced, in uniseriate rows (Figs 63,66,67). Striae are occluded by' cribra on the outer surface (Figs 63,65-67). Areolation continues down the mantle but leaves a plain, narrow mantle edge (Fig.63). Pore fields occur at both apices and extend onto the valve face; they consist of long bars intermittently separated by shorter crosssections (Figs 63-65). A rimoportula is situated adjacent to the apical pore field (Figs 63,65). It has an unusual structure in that the inner lip is smaller than the outer lip (Fig.65; see also Hyalosynedva laevigata, Figs 17-19). The girdle consists of up to six bands, all incomplete and ligulate (Fig.64). Each band has two separate rows of areolae, one on the pars interior and one on the pars exterior, each pore closed by a cribrum (Fig.64). There is no distinction between bands except for a decrease in width in the abvalvar direction (Fig. 64). The valvocopula is identical to the other bands except that the pars interior has a simple lip to attach to the valve (Fig.64, arrowed). This species is usually figured as hyaline, un-ornamentated valves (e.g. Hustedt 1932). However, SEM examinations have revealed a detailed valve structure which distinguishes it from Synedva sensu stvicto and all the new genera described above. Neosynedra tovtosa (Grun.) Williams and Round, comb. et stat. nov. Basionym: Synedra provincialis var. tortosa Grunow (1877), p. 166, $193, fig.7. Type locality: Upolu, Samoa Islands, leg Dr. Graeffe. Type slide: Naturhistorische Museum Wien (not seen). Material studied: North and northwest side of island on coral reef. Collected on the Philippine Isles at Station no. 9. P.S. Moreland [sometime between 24th February 1973 and 10th March 19731. Epiphytic on algae from coast of Queensland, Australia. F.E. Round. with a distinct Valves elongate, undulating outline and slightly capitate to

rounded poles (Fig.68). The sternum is conspicuous and well developed (Figs 68-71); the areolae are evenly spaced in uniseriate rows (Figs 69-71). Striae are occluded by cribra on the outer surface (Figs 69-71). Areolation continues down the mantle but there is a plain mantle edge (Fig. 69). Apical pore fields as in previous species. A rimoportula is situated just in front of the apical pore field (Fig.71). The girdle consists of at least four bands, of similar structure to those in the previous species (Fig.69). This species is distinguished by the frequency of cross-member divisions in the apical pore field. It is easily identified by its undulating outline.

DISCUSSION Without repeating the arguments already put foward by Round (1984) concerning diversity, it seems clear to us that the araphid diatoms are more diverse than current classifications allow; there has been a tendency to unite them because they share a few characters with all other araphid diatoms. Under the light microscope much of the detail is difficult to resolve in these needle-like species. Many of the new genera that we have recognised had previously been suggested in some form by earlier diatomists who worked with live material as well as cleaned. Characters examined: (1) Valve striation. Each new genus described above has a unique component to its valve structure differentiating it from Synedva senm stvicto. Catacombas, Hyalosynedva and Neosynedra have been misunderstood when light microscopy alone was used. Hyalosynedva and Neosynedva were misinterpreted as so little of the valve fine structure is apparent in the light microscope and the two genera have been assumed to be closely related merely from the lack of structural detail - hardly a valid taxonomic criterion. However, in the SEM the valve structure of each is quite different. In Neosynedva the impression of a structureless inner surface, or at least that of very delicate striae, is due to the closeness of the striae and the nature of the closing plates. However, in Hyalosynedra, the inner surface is

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Revision of Synedra

Neorynedra tortosa.. Figs 68-70. Figs 68-71. Philippines, P. S . Moreland. Fig.71 Queensland, Australia. F.E. Round.

Fig.68.

External

view

of

whole

valve,

Bar=23 pm. Fig.69. Polar view of cingulum, Bar=3.8 pm. Fig.70. Detail of broken valve showing inter-connections, Bar=1.5 pm. Fig.71. Detail of polar pore-field note many crossmembers, Bar=3 pm.


336


structureless. Here, in LM, with good resolution and focusing through the inner layer, the striae can be seen faintly. SEM observations of the outer wall of the valve reveal a series of distinct striae with an unusual closing plate. Catacombas also has a doublelayered structure but has a more complex areolar system that can be seen clearly in the LM. The obvious difference between Hyalosynedva and Catacombas is that in the latter the striae are more robust and hence visible through the featureless inner wall. The valve mantle in Hyalosynedva is not distinct from the valve face and there is no break in the rows of areolae. In Catacombas the mantle is precisely at right-angles to the valve face with the striation broken at the junction and then continuing on the mantle. In cross-section it is seen that this sharp differentiation is caused by inter-connections between the transapical ribs. This results in the chambered appearance when the valve is seen in cross-section. In Tabulavia there are three different types of valve structure. Nevertheless, they all share the complex closing plate, albeit occupying varying degrees of the valve surface, plus a range of complexity in cribral structure. Ctenophova has a more conventional valve structure of almost equal sized valve ribs and cross-members. It differs primarily from Synedva sensu stvicto in the size of the pores and in the structure of the closing plate which is similar to that of the Catacombas and Hyalosynedva (See Granetti 1984, pl. 10, fig.4). (2) Apical Pore fields. It was previously considered that only two distinct type of porefield were present in Synedva. In the first the pore-field is formed by a reduction in size of the transapical ribs of the valve; the pores extending part way onto the valve face. The second type was termed the ocellulimbus and was thought to be restricted to various subgroups of Synedva (Williams 1986). Catacombas, Hyalosynedva, Tabulavia and Ctenophova all share the ocellulimbus. This structure was defined as “...composed of a plate set into the polar valve mantle”. Neosynedva has a pore-field that occupies the polar valve mantles and part of the adjacent valve face. In general it is composed of a series of rows of horizontal bars and apertures which very occasionally are interrupted by smaller cross-members. There are no occlusions between these bars. A

somewhat similar type of pore field is present in Protoraphis Hustedt and Krasske (Gibson 1979) and in Cyclophova (Navarro 1982; Round, Crawford and Mann, in prep.). The latter has a vertical silica bar which divides the pore-field in two parts. ( 3 ) Rimoportulae. All the genera described above have rimoportulae. Catacombas, Hyalosynedva, Ctenophova and Neosynedva have a single rimoportula at each pole adjacent to the pore-field. Tabulavia has only a single rimoportula situated near one of the porefields. However, the occasional specimen has been recorded with two per valve and then the additional process is located adjacent to the opposite pore-field (e.g. Synedva fasciculata var. pavva and S. investiens in Poulin et al. 1984). The rimoportulae differ slightly in their morphology. Catacombas has the process extended on a slight stalk proud of the internal surface of the valve, whilst in Neosynedva and Hyalosynedva the inner lip is in the form of a simple notch and the outer lip is curved around it. Externally it is simply a small perforation in the valve structure. This type of rimoportula is present in Thalassionema (Hallegraeff 1986) and so far appears to be confined to marine genera.

Catacombas, Hyalosynedva, (4) Girdle. Tabulavia and Ctenophova all share a similar type of girdle construction, with Neosynedva being distinct from all of these. In all the genera the girdle is composed of open, ligulate bands. In Catacombas, Hyalosynedra, Tabulavia and Ctenophova all the valvocopulae are plain bands with no perforations. The mode of attachment to the valve is distinctive. Catacombas and Hyalosynedva have a smooth, continuous edge which folds slightly under the rim of the valve mantle. The pars interior does not extend any distance into the valve interior and so is unaffected by the inner valve structure. In Tabulavia and Ctenophova there is a continuous pars interior to the valvocopulae but the edges are slightly crenulated to accord with the valve rib structure.

The distinction of copulae is problematical. In Catacombas and Hyalosynedra the band which directly follows the valvocopula is distinctive enough to be differentiated morphologically. It is much


Revision of Synedra

larger with a deeper ligula but is still nonareolate. This could be considered as a single copula. In Tabulavia and Ctenophova the copulae are distinguished by the presence of a single row of poroids along the upper part of the pars interior. Finally, Catacombas and Hyalosynedra have two and one pleurae respectively, distinguished by the presence of a single row of poroids along the inner edge of the bands. Tabularia has possibly a single pleura distinguished by the size and general structure of the ligulae. It is not certain whether Ctenopkora has this final pleural band. In contrast Neosynedra is quite different. There are up to six bands, all identical and all with two rows of poroids along the pars interior and pars exterior. The areolation of the bands occupies a large area; the cribra are similar in structure to those of the valve. The valvocopula is distinguished only by its position. There is a slightly curved internal edge which facilitates attachment to the valve. The girdle of Neosynedva bears a close resemblance to that of Protoraphis (Gibson 1979) rather than to those of the other genera described above.

(5) Chromatophores. Information on chromatophore distribution is not complete and needs further study. It has been well documented that Catacombas gaillonii has many small plates (Karsten 1899). Ths chromatophore structure of Hyalosynedra is unknown except for a report from Mereschkowsky (1902) of four plates for a species that he tentatively identified as Synedvu laevigata. The situation is somewhat confusing in Tabularia with both small plates and large plates being recorded. However, it is clear that regardless of the number of chromatophores, they are all still plates of one sort or another. In Catacombas there are discoid chromatophores similar to some other marine araphids such as Thalussiothrix Cleve & Grunow (Karsten 1899). T w o plates have been recorded for Ctenopkora pulckella (Pfitzer 1871). The ultrastructure of the above genera indicates quite clearly that not all former Synedra species are closely related. From the data above it is considered that Catacombas, Hylaosynedra, Tabularia and Ctenopkora share certain features, in particular the ocellulimbus,

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details of girdle structure and closing plate. The relationships of the genera with an ocellulimbus will be discussed in greater detail in a further paper (Williams and Round, in prep.). However, Neosynedra is quite different in all the above respects and shares very few characters with the other genera. It seems that Neosynedra shares more distinctive features with Protoraphis than with the other taxa: However, this has not been studied in detail; the comparison may also extend to Pseudohimantidium (Rivera, Gonzales and Barrales 1986). Araphid diatom taxonomy has yet to progress further than the descriptive phase and in some publications the diversity of these taxa is being de-emphasised due to the possession of a few common features. Previously it has been shown that Ardissonia and T o x a r i u m are quite distinct marine genera (Round 1979) and that Synedra should be restricted to a group of freshwater species (Williams 1986). Thalassiotkrix, Tkalassionema and Synedrosphenia have all been previously separated and considered quite distinct (Cleve and Grunow, 1880; H. and M. Peragallo, 1897-1900). The problem of the overlap between some of the Synedra species (e.g. Synedra rumpens Kutz.) with some of the Fragilaria species (e.g. Fragilaria vauckeriae (Kutz.) Petersen) will be dealt with in a further paper. We have not been able to study in detail all of the described Synedra species, a task far too great for just two authors. However, we do suggest that the genera above studied give a preliminary indication of the diversity that exists within the Synedroid taxa.

ACKNOWLEDGMENTS We would like to thank the following for providing us with material used in this study: A. Cardinal, J. Mercer and M. Kuylenstierna. Dr. N.K.B. Robson and Marion Short gave invaluable assistance with the latin descriptions.

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REFERENCES AGARDH, C.A. (1812). Dispositis Algarum Suecae. Lund: Litteris Berlingianus. AGARDH, C.A. (1832). Conspectus Criticus Diatomacearum. Lund, part 4, pp. 48-66 ARCHIBALD, R.E.M. (1983). The diatoms of the Sundays and Great Fish Rivers in the Eastern Cape Province of South Africa. Bibliotheca Diatomologica, 1. 362pp. J. Cramer, Vaduz. BORY DE SAINT-VINCENT, J.B.M. (1827). EncylopCdie MCthodique Histoire Naturelle des Zoophytes, ou Animaux RayonnCs, faisant suite a I’histoire naturelle des vers, de Bruguikre. [Par: M.M. Lamaroux, Bory de Saint-Vincent et End. Deslongchamps]. Paris, Agasse, Imprimeur-Libraire, rue des Poitevins no.6. pp. 377-819 BRUN, J. (1880). Diatomtes des Alpes et du Jura et de la Rtgion Suisse et Francaise des environs de Genkve. 146pp., 9 pls. C. Schuchardt, Geneve CHOLNOKY, B.J. (1963). Ein Beitrag zur Kenntnis der Diatomeenflora von HollandischNeuguinea. N o v a Hedwigia, 5, 157-198 CLEVE, P.T. & GRUNO.W, A. (1880). Beitrage zur kenntniss der arctischen Diatomeen. K.svenska Vetensk.-Akad.Handl., 17, 121 pp. CLEVE-EULER, A. (1953). Die Diatomeen von Schweden und Finnland. K.svenska Vetensk.Akad.Handl., 4(5), 1-225 EHRENBERG, C.G. (1830). Beitrage zur Kenntnis der Organisation der Infusorien und ihrer geographischen Verbreitung besonders in Sibirien. Ab.Akad.wiss., Berlin, 1832, 1-88 EHRENBERG, C.G. (1832). Uber die Entwicklung und Lebensdauer der Infusionsthiere; nebst ferneren Beitragen zu einer Vergleichung ihrer Organischen Systeme. Ab.Akad.wiss., Berlin, 1832, 1-154. EHRENBERG, C.G. (1838). Die infusionsthierchen als vollkommende Organsimen. 548pp., 64 pls. Leopold Voss, Leipzig. FRENGUELLI, G. (1929). Diatomee fossili delle conche saline del desert0 Cileno-Boliviano. Boll.Soc.geo/.ital., 47, 185-236 F.RENGUELL1, J. (1942). Diatomeas del Neuquten (Patagonia). Revta Mus. L a Plata, secc.Bot., 5, 73-219 GEMEINHARDT, K. (1926). Die Gattung Synedva in systemischer, zytologischer und okologischer Beziehung. Pflanzenforschung, 6, 88 PP. GIBSON, R.A. (1979). Pvotovaphis atlantica sp. nov., a new marine epizoic diatom. Bacillaria, 2, 109-126 GRANETTI, B. (1984). Le diatomee del lago Trasimeno: Sistematica ed Ecologia. Riv.ldvobiol., 23, 3-112

GREVILLE, R.K. (1824). Scottish Cryptogamic Flora. Vol. 2, 61- 120, Edinburgh and London GRUNOW, A. (1862). Die osterreichischen Diatomeen nebst Anschluss einiger neuen Arten von ,, andern Lokalitaten und einer kritischen Ubersicht der bisher bekannten Gattungen und Arten. Erste Folge. Epithemieae, Meridioneae, Diatomeae, Entopyleae, Surirelleae, Amphipleureae. Vevh.zoo1 .-bot. Ges. Wien, 12, 315-472 GRUNOW, A. (1877). New diatoms from Honduras. Mon.Microsc.J., 18, 165-186 HALLEGRAEFF, G.M. (1986). Taxonomy and Morphology of the Marine Plankton Diatoms Thalassionema and Thalassiothvix. Diatom Research, 1(1), 57-80 HOLMES, R.W. & CROLL, D.A. (1984). Initial observations on the composition of dense diatom growths on the body feathers of three species of diving seabirds. In : Pvoceedings o f t h e Seventh International Diatom Symposium (D.G. Mann, ed.), 265-277. Otto Koeltz, Koenigstein. HUSTEDT, F. (1932). Die kieselalgen Deutschlands, Osterreichs und der Schweiz unter Berucksichtigung der ubrigen Lander Europas sowie der angrenzenden Meeresgebiete. In: Dv.L. Rabenhorst’s Kvyptogamen-Flora von Deutschland, Osterveich und dev Schweiz, 7: 2(2), 177-320 JUHLIN-DANNFELT, H. (1882). O n the diatoms of the Baltic Sea. Bih.K.svenska Vetensk.Akad.Handl., 6 (21), 52 pp. KARSTEN, G. (1899). Die Diatomeen der Kieler Bucht. Wiss. Meevesunters. (Kiel), 4, 19-205 KUTZING, F.T. (1844). D i e Kieselschaligen Bacillarien odev Diatorneen. Nordhausen, 152 pp., 30 pls. KUTZING, F.T. (1849). Species Algavum. F.A. Brockhaus, Lipsiae, 922pp. LAGERSTEDT, N.G.W. (1876). Saltvattens Diatomaceer frin Bohuslan. Bih. K m e n s k a Vetensk.-Akad.Handl., 3(15), 66pp. LANGE-BERTALOT, H. (1980). Zur systematischen Bewertung der Bandformigen Kolonien bei Navicula und Fragilavia. N o v a Hedwigia, 33, 723-787 MANN, D.G. (1978). Studies in the family Ph.D. Nitzschiaceae (Bacillariophyta). Dissertation, University of Bristol MA”, D.G. (1982). Structure, life history and systematics of Rhoicosphenia (Bacillariophyta). I. The vegetative cell of R h . cuvvata. ].Phycol., 18, 162-176 MERESCHKOWSKY, C. (1902). Les types de Scvipta l’endochrome des diatomkes. Bot.Horti. Univevs. Imp .Petyopol., 21, 107-193 NAVARRO, J.N. (1982). A survey of the marine diatoms of Puerto Rico. IV. Suborder


Revision of Synedra

Araphidineae: Families Diatomaceae and Protoraphidaceae. Botanica mar., 25, 247-263 PATRICK, R. & REIMER, C.W. (1966). The diatoms of the United States. Monogr.Acad. Nat.Philadelphia, 13(1), 686 pp. PERAGALLO, H. & M. (1897-1908). Diatomees Marines de France et des Districts Maritimes Voisins. Micrographie-Editeur, Grez-surLoing. PFITZER, E. (1871). Untersuchungen iiber Bau und Entwicklung der Bacillariaceen (Diatomaceen). Bot.Abhand1. Morphologie Physiologie, 2 (ed. Hanstein), 189 pp. POULIN, M., BERARD-THERRIAULT, L. & CARDINAL, A. (1984). Les diatomees benthiques de substrats durs des eaux marines et saumitres du Quebec. 3. Fragilaroideae (Fragilariales, Fragilariaceae). Naturaliste can., 111, 349-367 PRITCHARD, A. (1861). A History of Infusoria. 4th ed. 968 pp., 40 pls. Whittaker and Co., London. RIVERA, P.S., GONZALES, H.E. & BARRALES, H.L. (1986). Cingulum and valve morphology of Pseudohimantidium Hustedt and Krasske (Bacillariophyceae). Phycologia, 25, 19-27 ROSS, R., C O X , E.J., KARAYEVA, N.I., MA", D.G., PADDOCK, T.B.B., SIMONSEN, R. & SIMS, P.A. (1979). An

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amended terminology for the siliceous components of the diatom cell. Nova Hedwigia, Beih., 64, 513-533 R O U N D , F.E. (1979). The classification of the genus Synedra. Nova Hedwigia, Beih., 64, 135146 R O U N D , F.E. (1984). The circumscription of Synedra and Fragilaria and their sub-groupings. In : Proceedings of the Seventh International Diatom Symposium (D.G. Mann, ed.), 241-253. Otto Koeltz, Koenigstein. SCHONFELDT, H. von (1907). Diatomaceae Germaniae. 263 pp., 19 pls. W. Junk, Berlin SMITH, W. (1853-56). Synopsis of the Britirh Diatomaceae. Vols 1 & 2, 89pp. & 107pp., pls 160; 61-62; A-E. John Van Vorst, London STOSCH, H.A. von (1975). An amended terminology of the diatom girdle. Nova Hedwigia, Beih., 53, 1-35 TEMPERE, J. & PERAGALLO, H. (1909). Diatomtes du Monde Entier. Edition 2, Arcachon, Grez-sur-Loing. Fasc. 8-12, 113208 VAN HEURCK, H. (1881). Synopsis des Diatomtes de Belgique. Atlas, pls 37-77. Ducaju et Cie, Anvers. WILLIAMS, D.M. (1986). Comparative morphology of some species of Synedra with a new definition of the genus. Diatom Research, 1(1), 131-152