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 itapariensis A.C. Pereira, J.T.S. Alves, J.P. Kociolek & S. Melo , sp. nov . (LM: Figs 19–25 ) Individuals examined for morphological analyses: 15 Valves linear-elliptical to elliptic-lanceolate with slightly undulate margins, middle inflated, with strongly protracted capitate apices ( Figs 19–25 ). Valve length 59.56–66.30 µm (average 64.01 µm; standard deviation ± 2.13 µm) and breadth 13.4–15.1 µm (average 14.00 µm; standard deviation ± 0.52 µm). Axial area narrow, linear from center to apex, length/breadth ratio 3.19–4.12. Central area transapically elliptical to rhombic in shape. Raphe filiform, external proximal raphe endings recurved in opposite directions and distal raphe endings appearing bifurcate formed by triangular laciniae ( Figs 24–25 ). Striae ( 19–20 in 10 μm) radiate to slightly oblique at the center becoming slightly convergent slightly towards the apices. One or two Voigt faults present on the secondary side of the valve are clearly recognizable by a single row of areolae separated from the striae ( Figs 21–23 ). Areolae evenly spaced, rounded to elongate linear-elliptical in shape. Each row with density of 8–9 areolae in 5 µm. One wide longitudinal canal is present along each valve margin. Type: — BRAZIL . Pará : Tapari Lake 02º26’22”S , 54º53’37”W , 16 December 2018 , Pereira, A.C.P. , sediment, station 1, ( Holotype HSTM –Algas slide no 16827!, here illustrated as Figure 23 , row sample; isotype HAS 6897 ! here illustrated as Figure 22 ) . Etymology: —The specific epithet is dedicated to study area from which it was collected, Itapari Lake. Itapari has the origin in the Nheengatu indigenous language of the Amazonian region, that means ita= stone + pari= surrounded, in other words, surrounded by stones. Observations: — Neidium itapariensis shares features with two species: Neidium borari and Neidium vandusenense Hamilton et al . (2019: 48) . Neidium vandusenense , described from Livingstone Lake in Vancouver, Canada , differs from N. itapariensis by its greater length and width, finer striae density in 10 µm, apiculate extended apices and three or more longitudinal canals. Neidium itaparienses resembles N. borari with respect to general valve outline, length, axial and central area, and longitudinal canals. However, N. borari is broader and differs by having straight, drop-like shaped proximal raphe endings as well as parallel striae at the center. We summarize the differences between the new species and the most similar taxa in Table 3 .