Envekadea metzeltinii, Lee & Tobias & Vijver, 2013

Lee, Sylvia S., Tobias, Franco A. C. & Vijver, Bart Van De, 2013, Envekadea metzeltinii sp. nov., a new diatom (Bacillariophyta) species from the subtropical karstic wetlands of the Florida Everglades, U. S. A., Phytotaxa 115 (1), pp. 15-24 : 18-19

Envekadea metzeltinii sp. nov. ( Figs 2–15 )

Type: — Everglades National Park , Florida, U.S.A. , 25°28.935, -81°2.907, sample CERP 254 865 1 19, leg. Evelyn Gaiser, coll. date 3 rd of November 2011, slide no. BR-4310 (holotype National Botanic Garden of Belgium), slide no. PLP-225 (isotype University of Antwerp , Belgium), ANSP GC 58995 (isotype Academy of Natural Sciences of Philadelphia, Pennsylvania, U.S.A.) .

Frustules rectangular in girdle view. Valves linear with almost parallel margins, slightly gibbous in the central part, and broadly rounded apices. Valve length 31–70 µm, valve width 8–11 µm. Axial area narrow, linear. Central area almost absent. Raphe sigmoidal with small, straight proximal raphe endings. Distal raphe fissures are hooked, ‘golf club–like’, towards opposite sides widening to their ends. Transapical striae radiate throughout, weakly geniculate, 18–19 in 10 µm. Complex pattern of shortened central striae present. Near the apices, clear shift in stria orientation visible.

Ecology and Distribution: — Envekadea metzeltinii has so far been found in Florida (Everglades coastal marine and brackish wetlands), Mexico (Yucatan) and the Bahamas ( Hein et al. 2008). The new Envekadea species was present in low numbers (<1% relative abundance) in a brackish location with 3900 µS cm –1 conductivity, 6.5 pH, and 270 µ g g – 1 total phosphorus. Accompanying taxa include Envekadea pseudocrassirostris , Fragilaria synegrotesca , Mastogloia lanceolata , M. calcarea (Lee et al. submitted), and Diploneis oblongella .

Etymology: —The species is named in honor of our dear colleague and friend Mr. Ditmar Metzeltin (Hofheim, Germany) who was the first to recognize the peculiar nature of the new species.

Observations: — LM ( Figs 2–7 ): Valves linear with parallel margins. Central valve part gibbous in larger specimens, slightly convex in smaller valves. Valve dimensions (n=20): length 31–70 µm; width 8–11 µm, length:width 3.5–6.5 ( Table 2). Axial area narrow, less than 1/9 of the total valve width, linear, widening very slightly near the central area. Two ribs bordering the axial area clearly visible. Central area almost nonexistent. Fascia always absent. Raphe filiform, branches straight with weakly expanded, straight proximal raphe endings. Distal raphe fissures ‘golf club-like’, i.e., hooked towards opposite sides widening to their ends. Transapical striae slightly geniculate and clearly radiate, equidistant throughout the entire valve, 18–19 µm. In the central area, several irregularly shortened striae inserted in the normal striation pattern. Near the apices, a sudden shift in stria orientation present. Several very short striae inserted near the axial area. Areolae weakly discernible. SEM ( Figs 8-15 ): Striae uniseriate, composed of areolae showing a wide variability in size and shape ( Figs 8, 10, 11 ). Most areolae apically elongated, rectangular ( Fig. 12 ). Near the central area and the apices, areolae very irregular in shape, showing a higher density than in the rest of the valve ( Figs 9, 10, 11 ). Short silica outgrowths present inside the areolae ( Fig. 10 ). Enlarged hyaline zone separating the striae on the apices, delimited by the external distal raphe branches ( Fig. 11 ). External hymenes never observed due to severe oxidizing of the valves. Striae continuing uninterrupted onto the mantle ( Fig. 12 ). Narrow hyaline zone present near the mantle edge ( Fig. 12 ). External raphe branches running in a rather deep, narrow groove, straight to very weakly undulating ( Fig. 8 ). Proximal raphe endings straight, terminating in a depression, bordered by four slightly raised plates ( Fig. 9 ). Inside the depression, a raised nodule visible on which the proximal endings terminate ( Fig. 9 , arrow). Distal raphe endings forming a hooked widening groove ( Fig. 11 ). Raphe branch, however, diverging from the external groove, continuing on a straight course ( Fig. 11 ). External distal endings terminating in opposite directions at the two poles, giving the raphe a sigmoid path ( Fig. 8 ). Internally, striae located between clearly raised virgae, composed of rounded, unoccluded areolae ( Figs 13, 15 ). Near the central area, striae diminishing in width towards the axial area ( Figs 13, 14 ). Internal raphe branches situated on a raphe sternum between two clearly raised, narrow costae running from apex to apex ( Figs 13, 14 ). At the central area, area between costae slightly widening ( Fig. 14 ). Near the apices, costae diverge, forming a plate-like, rounded, hyaline zone, showing the sigmoid course of the raphe ( Fig. 15 ). Proximal internal raphe endings hooked ( Fig. 14 ). Distal raphe endings terminating on short, simple helictoglossae ( Fig. 15 ).

Due to the rarity of the new taxon and the severe cleaning procedure, no frustules in girdle view have been observed. Details on the girdle are therefore lacking.

Figures

FIGURES 2–7: Envekadea metzeltinii. LM images. Fig 2: Specimen from Water Conservation Area 3A, Florida, U.S.A. (25°52.761, -80°41.476) collected by F. Tobias on November 17, 2009 (refer to Fig. 1). Figs 3–7: Specimens from holotype material. Scale bar represents 10 µm.

FIGURES 8–12: Envekadea metzeltinii. SEM images. Fig. 8: External view of an entire valve showing wide variability in size and shape of the areolae and the sigmoid course of the raphe. Fig. 9: Detail of external central area showing the proximal raphe endings, terminating in a depression, bordered by four slightly raised plates. The arrow highlights the raised nodule. Fig. 10: Detail of external valve apex showing irregularly-shaped areolae with short silica outgrowths inside. Fig. 11: Detail of the distal raphe fissure and enlarged hyaline zone. Fig 12: Detail of external valve mantle showing uninterrupted striae and a narrow hyaline area near mantle edge. Scale bar represents 10 µm in Fig. 8 and 1 µm in Figs 9–12.

FIGURES 13–15: Envekadea metzeltinii. SEM images. Fig. 13: Internal view of valve showing axial costae and unoccluded areolae. Fig. 14: Detail of internal central area showing slight widening of axial costae. Fig. 15: Detail of internal valve apex showing divergence of axial costae and simple helictoglossae. Scale bar represents 10 µm in Fig. 13 and 1 µm in Figs 14–15.