The diatom genus Ctenophora: A discussion on its morphology, relationships, and some species Author Williams, David M. 0000-0002-0584-307X The Natural History Museum, London, UK. d.m.williams@nhm.ac.uk Author Vijver, Bart Van De Research Department, Meise Botanic Garden, Meise, Belgium. & Department of Biology - ECOBE, University of Antwerp, Wilrijk, Belgium. text Phytotaxa 2023 2023-12-27 632 1 1 26 https://phytotaxa.mapress.com/pt/article/download/phytotaxa.632.1.1/51385 journal article 10.11646/phytotaxa.632.1.1 1179-3163 10435352 Ctenophora pulchella (Kütz.) D.M.Williams & Round ( Figs 1–31 ) Basionym: Synedra pulchella Kütz. 1844: 68 , pl. 29, fig. 87 (see Figs 1, 2 ) Synonyms: Exilaria pulchella Ralfs ex Kütz. 1844: 68 , nom. nud. Ctenophora pulchella Bréb. ex Kütz. 1849 : nom. nud. Ctenophora pulchella (Kütz.) H.Schönf. 1907: 104 , 248 Fragilaria pulchella (Kütz.) Lange-Bert. 1980: 749 Registration: http://phycobank.org/104119 ( type ) Valves lanceolate, gently tapering towards sub-capitate poles; length ca. 48–59μm, width ca. 2–4μm ( Figs 4–11 ). Sternum very narrow, but linear, regular, slightly narrowing towards poles ( Figs 17–19 ). Sternum meets at roughly square to broadly circular-oblong shaped ‘central area’, buttressed either side of valve ( Figs 4–11 , 19 ; arrow in 27 and 30); buttressing composed of modified virgae enclosing clear hyaline area (= ‘central area’), ‘ghost striae’ barely visible ( Figs 4–11 , 19 , 27, 30 ). Sternum meeting and coalescing with virgae, both ca. same size, vimines reduced in size relative to virgae ( Figs 17–19 , 25, 26 ), appearing as mesh-work with ca. 4–8 strutted closing plates. Striae (= virgae+vimines) 13–14 (?) in 10μm, areolae ca. 20 (?) in 10μm, regularly spaced, parallel ( Figs 25, 26 ), extending onto mantle, in 2–4 ‘rows’ ( Figs 17–19 , 29 ). Apical pore field as ocellulimbus (sunken pore field), composed of 6 x 8 rows/ columns of pores, situated entirely on valve mantle ( Figs 16 , 24, 25 ). Marginal spines absent, but faint thickenings overhanging ocellulimbus ( Figs 16 , 25 ). Rimoportulae simple, composed of (internally) paired lips situated on or adjacent to virga, externally occurring between virgae, one at each pole ( Figs 16 , 18 , 22–25 ). Irregularly spaced, uneven silica plaques situated on mantle edge ( Figs 16 , 27 , dashed arrow, 29). Girdle composed of two (?) open bands, VC plus one C ( Figs 14 , 20, 21 , 28, 29, 31 ); VC plain, pi with crenulated edge to fit virgae, central smooth area to fit ‘central area’ ( Fig. 31 ); pe separated with ridge, ca. four times larger than pars interior ( pi ) ( Figs 29, 31 ). Open portions of VC meet at pole, aligned horizontally ( Figs 14 , 20, 21 , 28 ). FIGURES 1–12: Ctenophora pulchella . Fig. 1, reproduction of the original drawing of Synedra pulchella from Kützing (1844 : pl. 29, fig. 87); Fig. 2, reproduction of the original description of Synedra pulchella from Kützing (1844: 68) ; Fig. 3, reproduction of de Brébisson’s note on ‘ Exilaria licmoidea ’ from ( Brébisson 1838: 41 ); Figs 4–11, LM micrographs of type specimens of Synedra pulchella (Figs 4–7, BM 18310, Figs 8–10, BM 18309, Fig. 12, colony from BM Adams Eul. 38. Scale bars = 10μm. FIGURES 13–16: Ctenophora pulchella (Ralfs, BM herb.). SEM micrographs, Fig. 13, external view of whole valve; Fig. 14, external view of portion of valve, to the right a portion of the VC with undulating pi and plain ‘space’ for the attachment at ‘central area’; Fig. 15, details of stria structure showing shape of areolae, virgae and portion of sternum; Fig. 16, external view of pole, with ocellulimbus and rimoportula. Scale bars = 1μm (Figs 15, 16), = 2μm (Fig. 14), = 10μm (Fig. 13). FIGURES 17–21: Ctenophora pulchella (Ralfs, BM herb.). SEM micrographs, Fig. 17, internal view of entire valve with VC at one side; Fig. 18, detail of pole, internal view showing rimoportula, virgae, vimines and sternum; Fig. 19, detail of central with enlarged (or modified) and (in this specimen) a vague appearance of ‘ghost striae’; Fig. 20, entire VC; Fig. 21, detail of 2 nd (?) band (copula) with ‘areola’–like ornamentation along its length. Scale bars = 2μm (Figs 18, 19, 21), 10μm (Figs 17, 20). FIGURES 22–26: Ctenophora pulchella . SEM micrographs, Fig. 22, external view of whole valve; Fig. 23, internal view of whole valve; Fig. 24, detail of pole, internal view showing, virgae, vimines and sternum; Fig. 25, details of pole, external view of ocellulimbus, rimoportula and areolae; Fig. 26, detail of striae, external view of virgae, vimines, sternum and closing plates. Scale bars = 1μm (Figs 24–26), 10μm (Figs 22, 23). FIGURES 27–31: Ctenophora pulchella (“ Exilaria licmoidea Breb. , Exilaria pulchella Ralfs ?! 160”, BM herb. Diat. 2542!). SEM micrographs, Figs 27 and 30, detail of central area showing buttressed central area (arrows); one plaque in the series indicated with dashed arrow. Fig. 28, details of pole with VC in situ , arrow indicated where arms meet; Fig. 29, detail of VC, white arrows indicating area of attachment to valve, irregular plaques indicated by dashed arrow; Fig. 31, detail of VC with attachment points to valve, undulating to fit virgae, plain to fit central area (arrows). Scale bars = 1μm (Fig. 28), = 2μm (Figs 27, 29, 30, 31). TYPE:— ENGLAND , Penzance , [John] Ralfs ( BM 18310 ! [Kützing 193], lectotype designated here, https://data.nhm.ac.uk/object/ 9545df61-a24c-4fa8-a796-e11279a9e9f4; BM 18644 ! (Kützing 360 [ March 1844 ] ; BM s.n.! and BM Adams Eul. 38! = Eulenstein, Diatomacearum species typicae no. 38 , “b) Penzance, Angl. In aqua dulci ” […] b) Spec. originale. Ktz. Bac. tab. 29. fig. 87 = Fig. 12 ]; “ Exilaria pulchella n. sp. , on aquatic plants, Penzance, Feb., 1840, J. Ralfs”, BM herb. Diat. 2536!; “ Exilaria pulchella . Kutz. Kies. Bacil. t. 29. f. 87, Penzance” [ British Algae , dried specimens of marine and freshwater algae, including the Desmidieae and Diatomaceae , volume 1, no. 34, 1850, see Ann. Mag. Nat. Hist. 2 (7), 412, 1850–1?, for date see Ann. Mag. Nat. Hist. 2 (7): 412, 1851 and Sayre 1969: 971 , “ Exilaria pulchellum ”]; “Penzance, Mr. Ralfs”, Diat. Herb. diat. 2534!, W. Smith, BM 23735–6!; L4020117!, Penzance, Herb. Lenormand https://data.biodiversitydata.nl/naturalis/specimen/L.4020117, FH : J. W. Bailey coll. E337 (http://www2.huh.harvard.edu/diatom/baileycat.htm), and ANSP : Febiger 3049, ‘ Exilaria pulchella Ralfs ex Kutzing’ (I = isotype ). 1 The History of the Collections contained in the Natural history departments of the British museum [...], cited by Sayre (1969: 175) , notes “c. 1850”. ADDITIONAL MATERIAL:— ENGLAND , Ilfracombe , Ralfs ( BM 18575 ! [Kützing 947]) WALES , Bangor , Aug. 1841 , J.R. [alfs], herb. Diat. 2536 ! FRANCE , Falaise ( BM 18308 ! [Kützing 1731]); BM 18309 ! , BM 18913 !, Mortain, “ Ctenophora pulchella Breb. Synedra Kg. ” (Kützing 1571 [Brébisson 407] [= Ctenophora pulchella Bréb. in litt. ] ; BM 2533 ! “ Ctenophora pulchella Bréb. | Exilaria Ralfs. Mortain ”, J. W. Bailey Coll. E338 (http://www2.huh.harvard.edu/diatom/baileycat.htm) . The protologue for Synedra pulchella notes for the locality that only “Originalexemplare wurden mir von dem Hrn. Berkeley mitgeteilt [Original specimens were given to me by Mr. Berkeley]” ( Kützing 1844: 68 ) and adds the name “ Exilaria pulchella Ralfs ! (ex specimen)”. Further details were provided in Kützing (1849: 46) : “ Ad Conferveas in aqua dulci Angliae et Galliae.—Specimina communicaverunt cl. Ralfs et De Brebisson. (v. s.) ”. In BM , four slides are listed as having specimens of Synedra pulchella (there are no species catalogued under the name Ctenophora ) in Kützing’s collection: BM 18308–18311 (there are a number of other Ralfs’ slides in BM other than in Kützing’s collection). BM 18310 (‘Kützing 193’) is described in the unpublished notebook to the collection as ‘ Exil. pulchella Ralfs Penzance (Ralfs hand)’. There are no notes for BM 18308, 18309 or 18311 (‘Kützing 1340’, ‘Kützing 1571’ or ‘Kützing 1731’, respectively) but all three were acquired from de Brébisson: two from Falaise, the third from Vire, both localities in Normandy , France (summarised in Table 1 ). TABLE 1: The four slides in BM catalogued for Synedra pulchella .

BM no.	Kützing no.	Locality	Collector	Taxon name
18308	1731	Falaise, France	Brébisson	Synedra pulchella [ pulcherimma ]
18309	1571	Mortain, France	Brébisson	Synedra pulchella
183101	193	[Penzance]	Ralfs	Synedra pulchella
18311	1340	Vire, France	Brébisson	Synedra pulchella [ Exilaria licmoidea ]

1 With an extra label on the reverse of the slide: “ Synedra pulchella Kg. det. R. Patrick” In addition, the notebooks list Kützing’s collection numbers 943–954 as being from ‘Berkeley’, presumably meaning Miles Joseph Berkeley (1803–1889), the donator of the ‘Originalexemplare’ noted in the protologue for Synedra pulchella . There are no specific comments in the notebook for ‘Kützing 948’ ( BM 17938, the slide label indicates the presence of Diatoma vitreum Kütz. ) or ‘Kützing 949’ ( BM 19285, the slide label indicates the presence of Striatella unipunctata (Lyngb.) C.Agardh ). For ‘Kützing 946’ (of which there is no prepared BM slide), ‘ Gomphonema dichotomum , Penzance, J. Ralfs’ is recorded and for Kützing 947 ( BM 18575) ‘ Encyonema prostratum , Berkeley Kg. ms (?) Ilfracombe Ralfs’ is recorded. The latter series of specimens and names is included here to demonstrate that collection numbers ‘Kützing 943–954’ were actually from Berkeley. ‘Kützing 948’ and ‘Kützing 949’ are marine samples, neither having any specimens of Synedra pulchella ; ‘Kützing 946’ and ‘Kützing 947’ are freshwater samples, but neither of those have any specimens of Synedra pulchella either (summarised in Table 2 ). Further material from Penzance in the BM is summarised in Table 3 . TABLE 2: Slides from Miles Joseph Berkeley in Kützing’s collection.

BM no.	Kützing no.	Locality	Collector	Taxon name
None	946	Penzance	Ralfs	Gomphonema dichotomum
18575	947	Ilfracombe	Ralfs	Encyonema prostratum
17938	948	Penzance	Ralfs	Diatoma vitreum
19285	949	Penzance	Ralfs	Striatella unipunctata

TABLE 3: Slides in Kützing’s collection from Penzance.

BM no.	Kützing no.	Locality	Collector	Taxon name [date from catalogue]
18644	360	Penzance	Ralfs	Gomphonema dichotomum [March 1844]
18670	377	Penzance	Ralfs	Gomphonema minutum [1842]
18953	479	Penzance	Berkeleya fragilis [March 1843]
19284	729	Penzance	Striatella unipunctata [Nov. 1842]
19301	744	Penzance	Rhabdonema arcuatum
17883	1347	Penzance	Striatella

With respect to the two names ‘ Exilaria pulchella ’ and ‘ Ctenophora pulchella ’, the following are relevant to their status: ‘ Exilaria pulchella Ralfs’, invalid (herbarium name): As noted above, several slides in BM (and elsewhere) can probably be considered part of Ralfs’ original material. These are all from Penzance, Cornwall , with Ralfs acknowledged as collector; some were acquired from Joseph Berkeley, others from de Brébisson. A packet of material in BM has the following on its herbarium label: “ Exilaria pulchella n. sp. , on aquatic plants, Penzance, Feb., 1840, J. Ralfs”. There is also material from Ralfs’ British Algae , dried specimens of marine and freshwater algae, including the Desmidieae and Diatomaceae ( Ralfs 1850 ) for “ Exilaria pulchella ” (no. 34; see Sayre 1969: 97 ). The name “ Exilaria pulchella (Ralfs) ” appears in Pritchard (1852: 482) , but in spite of numerous references to ‘ Exilaria pulchella Ralfs ex Kützing’ in much of the subsequent literature, most citations of this name are to the unpublished basionym for Ctenophora pulchella . As far as can be established, the name Exilaria pulchella has never been validly published by Ralfs or anyone else. ‘ Ctenophora pulchella Brébisson’ invalid (herbarium name): Kützing referred to ‘ Ctenophora pulchella Brébisson in litt. ’, based on specimens received from de Brébisson ( Kützing 1849: 46 , as does Smith 1853: 70 ). As noted above, in BM there are several possible sources for these specimens. The most likely ‘type’ (original, or more appropriately, ‘intended type’) specimens are those from Mortain, Normandy , France , labelled as “ Ctenophora pulchella Breb. ” (‘Kützing 1571’) (BM 18309, BM 18913, raw material in a packet on herbarium sheet ‘diat. 2533’, ‘Mortain’) [= ‘ Ctenophora pulchella Brébisson in litt. ’]. There is also material from Vire (‘Kützing 1340’) (BM 18311), labelled “ Exilaria licmoidea Breb. , Exilaria pulchella Ralfs ?! 160” (BM herb. Diat. 2542!), which is most likely the ‘intended type’ specimens of Exilaria licmoidea Bréb. ‘ Exilaria licmoidea ’ Brébisson 1838: 41 , invalid (no description, no illustration): Exilaria licmoidea first appeared in print as just a name and locality (“ EXILARIA LICMOÏDEA Nob. Vire ” Brébisson 1838: 41 , see Fig. 3 ). It was noted again, just with its name, in Brébisson (1839: 275) and Kützing (1844: 69) but has never been validly published. Material exists in BM ( FRANCE : Vire, “160 Synedra | Exilaria licmoidea Breb. , Exilaria pulchella Ralfs ?!”, ‘Kützing 1340’, BM 18311, see https://data.nhm.ac.uk/object/e2293b3c-8eee-423d-8815-ef57b85e2f12), which are specimens intended as types for Exilaria licmoidea . Inspection of this material yielded three different species, including what would be referred to as Ctenophora pulchella . Without a description or illustration, there is no rational way of deciding which of these three de Brébisson was referring to with his name Exilaria licmoidea .