Fragilaria fusa (R.M. Patrick) Wengrat, C.E. Wetzel & E. Morales, 2016

Wengrat, Simone, Morales, Eduardo A., Wetzel, Carlos E., Almeida, Pryscilla D., Ector, Luc & Bicudo, Denise C., 2016, Taxonomy and ecology of Fragilaria billingsii sp. nov. and analysis of type material of Synedra rumpens var. fusa (Fragilariaceae, Bacillariophyta) from Brazil, Phytotaxa 270 (3), pp. 191-202 : 194-196

Fragilaria fusa (R.M. Patrick) Wengrat, C.E. Wetzel & E. Morales , comb. et stat. nov. ( Figs 2–21 )

Basionym: Synedra rumpens var. fusa R.M. Patrick in Proceedings of the Academy of Natural Sciences of Philadelphia 62: 218, pl. 8: figs 6–8. 1940.

Valves are narrow and lanceolate, with attenuated and subcapitate apices ( Figs 2–14 ). Length 29.0–97.0 μm, width 2.5–3.0 μm. The central valve margin is inflated on both sides ( Figs 2–14 ). The axial area is lanceolate, with clear fascia at the central area ( Figs 4–6, 8–12, 14 ). Striae are distinct, parallel and alternate throughout the valve, 15–16 in 10 μm ( Figs 4–6, 8–14 ). Ghost striae faint ( Figs 4–6, 8–14 ). Areolae not discernible in LM. Ribbon-like colonies were not observed. SEM: External SEM images show striae composed of rounded areolae toward the apices and elongated areolae toward the valve center and on the mantle ( Figs 17, 18 ). Striae are interrupted by spines and continue onto the mantle ( Figs 16, 17 ), composed of a single areola at the apices, increasing up to five areolae toward the middle of the valve ( Fig. 15 ). Costae are wider than the striae and are raised ( Figs 15, 18 ). Spines are sharp cones ( Figs 15–18 ) located closer to the valve face/mantle junction ( Figs 15–18 ). Apical spines are absent or little developed ( Figs 15–18 ). Well-developed apical pore fields of the ocellulimbus type are located on the mantle at both valve ends ( Figs 16–18 ). Plaques are present along the abvalvar margin of the mantle ( Figs 16, 19 ). The cingulum is composed of three open copulae ( Figs 16–17 ) each with a single row of poroids on the pars interior that are partially obscured by overlapping copulae ( Figs 16, 17, 19 ). Girdle bands barely touching at open end ( Figs 16, 17 ). Internal SEM images show raised costae and sunken striae. There is one well-developed rimoportula, heavily silicified and slightly inclined with respect to the apical axis, and located on the axial area ( Fig. 21 ). Abvalvar side of mantle thick at valve apices ( Fig. 21 ).

Type:— BRAZIL. Ceará: Municipality of Maranguape, margins of ‘Açude São Bento’, F. Drouet (D) 5 August 1935 (holotype ANSP!, population on slide A-25422 illustrated here in LM as Figs 2–14 . Isotype ANSP!, population in material A-25079 illustrated here in SEM as Figs 15–21 ).

Distribution and ecology:— Fragilaria fusa has only been reported with illustrations from the type locality, ecological conditions of which are unknown.

Remarks:— Fragilaria fusa may be distinguished from the type of Fragilaria rumpens ( Kützing 1844: 69) G.W.F. Carlson ( Tuji & Williams 2006a: figs 1–18) by a combination of characters ( Table 2). Fragilaria fusa is narrower (2.5–3.0 μm), has lower stria density (15–16 in 10 μm), subcapitate apices, central area inflated on both sides, absent or little developed apical spines located near the junction between valve face and mantle, a well-developed rimoportula, heavily silicified and barely inclined with respect to the apical axis, girdle bands that are barely touching at open ends and with a thickened abvalvar side of mantle at valve apices. In contrast, F. rumpens produces ribbon-like colonies with linking spines, is wider (3–4 μm), has denser striae (18–20 in 10 μm), rostrate apices, a central area unilaterally or bilaterally gibbous, apical spines present and a well-developed, small rimoportula, less silicified and inclined at a wider angle with respect to the apical axis. Additionally, F. rumpens presents the terminations of girdle bands overlapping at open ends and the abvalvar side of its mantle has the same thickness as the rest of the mantle. Fragilaria fusa can also be misidentified as F. parva (Grunow in Van Heurck 1881: pl. 40: fig. 15) Tuji & D.M. Williams (2008: 29, pl. 2: figs 13–28) and F. pararumpens Lange-Bertalot et al. in Hofmann et al. (2011: pl. 8: figs 4–10), however F. fusa has lower stria density than both species ( Table 2). Fragilaria fusa also may be distinguished from F. tenera (W. Smith 1856: 98) Lange-Bertalot (1980: 746 , pl. 2: figs 1–6, pl. 4: figs 1–6) by some characters: F. fusa is wider (2.5–3.0 μm), has lower stria density (15–16 in 10 μm), apical spines absent or little developed and the rimoportula is well developed.

Figures

FIGURES 2–14. Type material of Fragilaria fusa. All LM pictures taken from the holotype population (A-25422). Light microscopy showing variation in size and valve outline. 4. Holotype specimen illustrated in Kingston (2003: fig. 12c). Scale bar = 10 μm.

FIGURES 15–21. Type material of Fragilaria fusa. All SEM pictures taken from the isotype population (A-25079). 15. External view of entire valve showing striae structure. 16–18. External view of girdle bands, spines and pore fields. 19. View of the mantle. 20, 21. Internal view of areolae and rimoportula. 16, 17, 19. Arrows indicate a single row of poroids on the pars interior of each copulae; poroids are partially obscured by overlapping copulae.