Taxonomy of three new Neidium Pfitzer species of the Arapiuns and Tapajós Rivers Basin (Santarém, Pará, Brazil) Author Pereira, Andreia Cavalcante Author Alves, Jannah Thalis Da Silva Author Vidal, Regiane Gabriele Rocha Author Kociolek, John Patrick Author Torgan, Lezilda Carvalho Author Melo, Sérgio text Phytotaxa 2023 2023-07-31 606 3 185 200 http://dx.doi.org/10.11646/phytotaxa.606.3.2 journal article 10.11646/phytotaxa.606.3.2 1179-3163 8202586 Neidium borari A.C. Pereira, S. Melo, L. Torgan, R.G.R. Vidal, J.P. Kociolek & J.T.S. Alves , sp. nov . (LM: Figs 2–11 , SEM: Figs 12–18 ) Individuals examined for morphological analyses: 30 Valves linear-elliptical to elliptical with strongly attenuated apices ( Figs 2–11 ). Valve length 52.15–67.90 µm (average 59.23 µm; standard deviation ± 3.37 µm) and breadth 15.36–17.75 µm (average 16.60 µm; standard deviation ± 0.74 µm). Axial area narrow, linear from center to apex, length/breadth ratio 3.19–4.12. Central area transapically rounded to rhombic in shape. In SEM, raphe filiform, external proximal raphe endings straight with drop-like shaped and distal raphe endings bifurcate formed by a broad triangular lacinia that extent to the base of the valve apex ( Figs 12–14 ). Each proximal helictoglossae forms two loosely interconnected ribbed nodules by a thin bridge of silica ( Figs 16, 18 ). Distal helictoglossae form prominent thickened nodules near the apices ( Figs 15, 17 ). Striae ( 16–18 in 10 μm) parallel at the center becoming slightly convergent at the apices. One or two Voigt faults present on the secondary side of the valve and clearly recognizable by a single row of areolae separated from the striae ( Figs 7–11 , 13 ). Areolae evenly spaced with rounded to linear-elliptical shaped, appearing more elliptical closer to the longitudinal canal. Each row with density of 5–7 areolae in 2 µm. One wide longitudinal canal is present along each valve margin that terminates at the valve apex ( Figs 13–14 ). Internally, areolae are covered by a hymen. Renilimbi are evident around areolae along the axial area and longitudinal canal regions, with 2–4 renilimbi. Renilimbi can be found randomly spread around areolae on the valve interior ( Figs 16–17 ). FIGURES 2–11. LM valve views of Neidium borari . Fig. 2, holotype. Fig. 5, paratype. Scale bar = 10 μm FIGURES 12–18. Neidium borari in SEM. Fig. 12. General external valve view. Fig. 13. Triangular lacinia that cover the distal raphe endings. Fig. 14. External view showing proximal raphe endings straight with drop-like shaped. Figs. 15, 17. Internally, distal raphe endings showing a prominent helictoglossae. Fig. 16. Proximal raphe endings form loosely interconnected ribbed nodules and evident renilimbi around areolae (arrows). Fig. 18. General internal valve view. Scale bars: Figs. 12, 18 = 10 μm; Figs. 15 = 5 μm; Figs. 13, 14, 16, 17 = 2 μm. Type: — BRAZIL . Pará : Jurucuí Lake 02º32’52”S , 54º58’21”W , 04 October 2016 , Pereira, A.C.P. , plankton, station 1, ( Holotype HSTM –Algas slide no 16826 !, here illustrated as Figure 2 , row sample; paratype HAS 6896 ! Verde Lake 02°29’34.9”S 54°56’51.5”W , 29 December 2016 , Pereira, A.C.P. , plankton, here illustrated as Figure 5 ) . Etymology: —The specific epithet is dedicated to indigenous people who live in lower Tapajós and Arapiuns Rivers region. A noun in apposition. Observations: — Neidium borari shares features with two known species: N. angustirostratum Lange Bertalot et al . (2003: 85) and N. statuarium Hamilton & Siver in Siver & Hamilton (2005: 364) . Lange-Bertalot et al . (2003) described N. angustirostratum from Sardinia and N. statuarium Hamilton & Siver (2005) was originally described from the Cape Cod peninsula in Massachusetts , USA . They both have smaller morphometric dimensions and higher numbers of striae in 10 μm ( Table 3 ) than N. borari . The similarity of N. borari with these species is in the valve outline, even though it is easily separated from both species which have curved proximal raphe endings. Neidium borari , on the contrary, has straight external proximal raphe fissures. Furthermore, N. angustirostratum differs by having a subparallel and moderately oblique striation pattern and central area that is rather small and obliquely elongated towards the margins. The most prominent feature in N. statuarium is seen in SEM, where surface depressions covering the longitudinal canal and central area can be seen. Comparison of N. borari to similar taxa is presented in Table 3 .