“Rediscovery” of Encyonema Ratpanati Sp. Nov. (Bacillariophyta, Cymbellaceae) in Victoria Falls, Namibia “Redescubrimiento” De Encyonema Ratpanati Sp
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Bol. R. Soc. Esp. Hist. Nat., 115, 2020: pediente de paginación “Rediscovery” of Encyonema ratpanati sp. nov. (Bacillariophyta, Cymbellaceae) in Victoria Falls, Namibia “Redescubrimiento” de Encyonema ratpanati sp. nov. (Bacillariophyta, Cymbellaceae) en las Cataratas Victoria, Namibia Adrián Llamazares, Eloy Bécares & Saúl Blanco Laboratorio de diatomología. La Serna 58, 24007, León, España. [email protected] Recibido: 17 marzo de 2021, Aceptado: 27 de abril de 2021. Publicado electrónicamente: 1 de mayo de 2021. Keywords: Diatom, New species, Taxonomy, Namibia, Africa. Palabras clave: Diatomea, Nueva especie, Taxonomía, Namibia, África. ABSTRACT An Encyonema population collected in the Zambeze River near the Victoria Falls, Namibia, is here described and illustrated in detail with the aid of LM and SEM microscopy. This taxon had already been presented in the literature under the name E. volkii, the reasons leading to treat this species as a new, independent taxon are here discussed. Encyonema ratpanati sp. nov. can be easily distinguished from E. volkii by its more linear outline (length-to-width ratio up to 4.3 vs. up to 3.5 in E. volkii), its lower degree of dorsiventrality, lack of rostrate apices throughout the whole diminution series, wider axial area and denser areolation (>26 lineolae per 10 µm and not 20–22 as in E. volkii). RESUMEN Se describe una población de Encyonema recogida en el río Zambeze, cerca de las cataratas Victoria, Namibia, y se ilustra en detalle con la ayuda de microscopía óptica y electrónica. Este taxón ya había sido presentado en la literatura bajo el nombre de E. volkii, se discuten aquí las razones que llevan a tratar esta especie como un nuevo taxón independiente. Encyonema ratpanati sp. nov. Puede ser fácilmente diferenciado de E. volkii por su contorno más lineal (cociente largo/ancho de hasta 4.3 vs. hasta 3.5 en E. volkii), su menor grado de dorsiventralidad, la ausencia de ápices rostrados a lo largo de toda la serie decreciente, el área central más ancha una areolación más densa (>26 lineolas cada 10 µm y no 20–22 como en E. volkii). 1. INTRODUCTION The genus Encyonema Kützing, 1834 is a relatively diverse group of freshwater diatoms, with about 300 species currently accepted in the scientific literature G( UIRY, 2021), most of them transferred from the genus Cymbella C.Agardh, 1830 or described as new species in the monograph by KRAMMER (1997). This group of biraphid diatoms is mainly characterized by a more or less developed degree of dorsiventrality, external terminal raphe endings bent towards the ventral side, and—generally—lack of stigmata or apical pore fields. Despite having been already proposed as a distinct genus in the XIX century (KÜTZING, 1833), most subsequent authors treated Encyonema taxa within Cymbella, merely distinguished by their their ability to form colonies in mucilage tubes. However, this feature is actually present in few Encyonema species, most of them living in mucous coatings on plants, wood or stones. It was not until 1982 when Encyonema was resurrected first as a subgenus K( RAMMER, 1982) and then recognized again as a genus, with an emended description (ROUND et al., 1990). The generitype E. paradoxum Kützing, 1834 resulted to be a later taxonomic synonym of E. leibleinii (C.Agardh) W.J.Silva et al., 2013, which retains nomenclatural priority (SILVA et al., 2013). Despite constituting a strongly supported monophyletic group (KERMARREC et al., 2011), there is a large heterogeneity among Encyonema members in terms of morphology as well as growth habit (LIU et al., 2021), so that taxonomy has undergone many changes doi: 10.29077/bol.115.ce03.llamazares ISSN: 2659-2703 -5- A. LLAMAZARES, E. BÉCARES & S. BLANCO (SILVA & SOUZA, 2015). Despite molecular data suggested a closer connection to the gomphonemoid clade (BRUDER & MEDLIN, 2007), the emplacement of Encyonema in the Cymbellaceae is now considered clear (NAKOV et al., 2014), in any case phylogenetically more primitive than other cymbelloid forms (PappaS, 2005). Prof. Ditmar Metzeltin (in LANGE-BERTALOT, 1993: pl. 134, figs 4-10) illustrated an Encyonema population collected in Kunene River (Namibia/Angola), assigned in that reference to the taxon Cymbella volkii Rumrich et al., 1993. In his reappraisal of the cymbelloid diatoms, KRAMMER (1997) reconsiders this population under the name “Encyonema sp.”, separated or, at least, doubtfully conspecific with (see the question mark in pp. 80) E. volkii (Rumrich et al.) Krammer, 1997. Here we present evidences supporting this segregation, describing and illustrating Encyonema ratpanati as a new species from samples collected near the Victoria Falls, Namibia. 2. MATERIALS AND METHODS A sample of epilithic algae was collected on littoral rocks in the Zambeze River, Zambia/Zimbabwe/Namibia border (17.92° S, 25.85° E, Figure 1), 50 m away from Victoria Falls. The sample fixed with weak formalin (about a 0.5% final concentration of formaldehyde) to stop biological activity in the sample. A suspension of clean diatom frustules was obtained from that sample in the laboratory by oxidation with hot (70–90 °C) hydrogen peroxide (30% v/v). Some drops of hydrochloric acid (3 M) were added to remove calcium carbonate inclusions. Light microscopy (LM) slides were mounted using Naphrax®. The identification of the diatom species were carried out at 1000× magnification using a DIC light (LM) Olympus BX60 microscope equipped with an OPTIKA camera. A subsample was analyzed by scanning electron microscopy (SEM) at the Electron Microscopy Unit (University of Jaen, Spain), by placing a drop of the cleaned sample on a conductive metal structure and allowing it to dry at room temperature. The samples were subsequently coated with a 10 nm thick gold layer using a modular high vacuum metallization system Figure 1. Type locality of E. ratpanati sp. nov. in the Zambeze River, (QUORUM Q150T ES). SEM images Namibia. were obtained using a MERLIN (Carl Zeiss) microscope operating at 20 kV. Images were processed with GIMP software (CHASTAIN & PFAFFMAN, 2006). 3. RESULTS Classification: Phylum Bacillariophyta Class Bacillariophyceae Order Cymbellales Family Cymbellaceae Encyonema ratpanati sp. nov. (Figures 2, 3). = Encyonema volkii pro parte (excl. typus) sensu LANGE-BERTALOT (1993, as “Cymbell volkii”, figs 139: 4–10),sensu KRAMMER (1997, as “Encyonema sp.”, fig. 69: 15),sensu KRAMMER (1997b, as “Encyonema volkii”, figs 191: 1, 2?, 3–5). -6- Comunicaciones especializadas “REDISCOVERY” OF ENCYONEMA RATPANATI SP.NOV. (BACILLARIOPHYTA, GOMPHONEMATACEAE) Diagnosis: valves lanceolate to subrhombic, somewhat dorsiventral, with a ventral margin less arched than the dorsal and slightly protruded (Figure 2). Apices acutely rounded, not protracted. Valve size (median [quartiles]): length 37.3 [37.1–37.8] µm, width 10.7 [10.5–10.9] µm. The axial area is widely lanceolate, broadening at midvalve but with no distinct central area (Figure 2). Stigmae or stigmoids absent. Raphe branches filiform near valve apices, broader in median portion (Figure 3A). Terminal raphe fissures Figure 2. Encyonema ratpanati sp. nov. LM. Individuals from the type externally curved towards the ventral population in valve view. Scale bar: 10 µm. margin, sometimes ending in valve mantle (Figure 3B). Central pores slightly bent dorsally, with a T-shaped intermissio (Figure 3C). Transapical striae subradiate, 5.8 [5.3–6.0] in 10 µm, equally spaced throughout the valve, formed by elongated lineolae (Figure 3), 27 [26–29] in 10 µm. Type: NAMIBIA: Zambeze River, near Victoria Falls, on rocks. Coll. E. Bécares, 10-VIII-2018. Holotype: LEB! DIATOMEA-29. Etymology: named after Ratpanat Expeditions SL, who organized the trip. Accompanying taxa: Encyonema ratpanati occurred along with Cavinula Figure 3. Encyonema ratpanati sp. nov. SEM. Individuals from the type scutelloides (W.Smith) Lange-Bertalot, population. A. Complete frustule in external oblique view. The striae continue throughout the mantle. The valve/mantle transi- 1996, Mastogloia danseyi (Thwaites) tion is soft. The raphe slit is wider in midvalve. B. Detail of the Thwaites, 1856, Placoneis apicalicostata apex and the valvocopulae. The distal raphe fissure is curved Metzeltin & Lange-Bertalot, 2002, towards the ventral side and ends externally in the mantle. C. Internal valve view of a theca. Note the T-shaped intermissio. D. and Sellaphora americana (Ehrenberg) Habitus. Note the perforated copula in the ventral side (frustule D.G.Mann, 1990. on the left). Differential diagnosis: best distinguished from Encyonema volkii by its more linear outline (length-to-width ratio up to 4.3 vs. up to 3.5 in E. volkii), its lower degree of dorsiventrality, lack of rostrate apices throughout the whole diminution series, wider axial area and denser areolation (>26 lineolae per 10 µm and not 20–22 as in E. volkii). The central protrusion is more evident also in E. ratpanati. Other Encyonema taxa with overlapping morphometric data include E. alpinum (Grunow) D.G.Mann, 1990, with a more elliptic outline (broader apices) and E. lacustre (C.Agardh) Pantocsek, 1901 (less dorsiventral, with radiate striae). Of interest is also comparison with similar Encyonopsis Krammer 1997 species such as Encyonopsis apiculata (Hustedt) Da Silva & Menezes, 2016 (with protracted apices), E. mendosa (Van Landingham) Da Silva & Menezes, 2016 (15 µm wide), E. lanceoelliptica Krammer, 1997 (less dorsiventral, wider axial area) or E. dubitata (Cholnoky) Krammer, 1997 (larger length-to-width ratio). Bol. R. Soc. Esp. Hist. Nat., 115, 2021 -7- A. LLAMAZARES, E. BÉCARES & S. BLANCO 4. DISCUSSION LANGE-BERTALOT et al. (1993) described Cymbella volkii from a sample collected in 1988 by Dr. O.H. Volk in algal crusts on mica rocks at Gross Barmen, Namibia. The type (‘Praep. Af-Fensteralgen 113 in Coll. Lange- Bertalot, Botan. Institut Universitat Frankfurt a.M.’) is illustrated in the same work (figs 134: 1–3), showing three individuals of an encyonemoid diatom that fits well with the description provided. In the same plate, another population collected at Kunene (Namibia/Angola border, figs 134: 4–10) is presented which, although identified also as C.