Neidium muyrakytan A.C. Pereira, J.P. Kociolek & S. Melo, 2023

Pereira, Andreia Cavalcante, Alves, Jannah Thalis Da Silva, Vidal, Regiane Gabriele Rocha, Kociolek, John Patrick, Torgan, Lezilda Carvalho & Melo, Sérgio, 2023, Taxonomy of three new Neidium Pfitzer species of the Arapiuns and Tapajós Rivers Basin (Santarém, Pará, Brazil), Phytotaxa 606 (3), pp. 185-200 : 191-196

Neidium muyrakytan A.C. Pereira, J.P. Kociolek & S. Melo , sp. nov. (LM: Figs 26–32 , SEM: Figs 33–39 )

Individuals examined for morphological analyses: 15

Valves linear to linear-lanceolate, margins parallel, slightly convex in the center with acute rounded apices ( Figs 26–32 , 33 ). Valve length 73.99–115.10 µm (average 86.45 µm; standard deviation ± 12.13 µm) and breadth 15.22– 20.77 µm (average 18.25 µm; standard deviation ± 1.66 µm). Axial area narrow, almost linear from center to apex, length/breadth ratio 3.92–5.75. Central area transapically rounded to elliptical in shape. In SEM, raphe lateral, external proximal raphe endings deflected hooks, bent at approximately 90 o angles in opposite directions from one another, and distal raphe endings bifurcate formed by broad triangular laciniae that extend to the base of the valve apex ( Figs 34–35, 36 ). Internally, each proximal helictoglossa forms two loosely ribbed nodules interconnected by a thin bridge of silica ( Fig. 39 ). Distal helictoglossae form prominent thickened nodules near the apices ( Figs 37–38 ). Striae (15–17 in 10 μm) oblique at the center becoming slightly convergent at the apices ( Figs 26–32 , 34–35 ). Externally, 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 26, 30–31 ). Areolae evenly spaced, rounded to elongate linear-elliptical in shape, appearing more elliptical closer to the longitudinal canal. Each stria with 4–5 areolae in 2 µm. Two or three wide longitudinal canals are present along each valve margin, and they are accompanied by irregularly-shaped pores at the apices of the valves ( Figs 33–34, 37 ).

TABLE 3. (Continued)

Type: — BRAZIL. Pará: Arapiuns River 02º20’01”S, 54º02’01”W, 15 December 2018, Pereira, A.C.P., plankton, station 1, (Holotype HSTM –Algas slide no 16828 !, here illustrated as Figure 26 , row sample; paratype HAS 6898 ! Verde Lake 02°26’21.7”S 54°56’23.3”W, 11 December 2012, Pereira, A.C.P., plankton, here illustrated as Figure 29 ) .

Etymology: —Muyrakyt„ (muiraquit„ in Portuguese) means “knot of trees” in Tupi language. It is the name given to various types of old artefacts of Amazonian indigenous origin that belong to Tapajó culture. They are carved in stone (green jade) or wood represented by frogs and often used as amulets. A noun in apposition.

Observations: — Neidium muyrakytan is morphologically similar to N. convolutum Liu & Kociolek in Liu et al. (2020: 172), N. rolandschmidtii Metzeltin & Lange-Bertalot (2007: 177) , N. sacoense Reimer in Patrick & Reimer (1966: 402) and N. sterrenburgii Metzeltin & Lange-Bertalot (2007: 180) by sharing several features: valve outline, axial area, central area and longitudinal canals. Neidium muyrakytan has a valve outline very similar to those observed in N. convolutum , N. rolandschmidtii and N. sterrenburgii . Recently, N. convolutum was described by Liu et al. (2020) from one sample collected from a wet wall of the hill near a stream in Shiwan Mountains National Forest Park, China. Neidium muyrakytan differs from N. convolutum mainly by their smaller dimensions and striae density. Another difference with N. convolutum is with respect to striation pattern at the apex which is more convergent in N. convolutum than N. muyrakytan . Furthermore, N. convolutum can be distinguished by the presence of some areolae positioned at the axial area next to the raphe and by being more rounded in outline than N. muyrakytan . Neidium rolandschmidtii was described from fossil sediments in Calado Lake, Amazon state. This taxon shares several features with our new species but differs by the larger morphometric dimensions, shape of the apices, striation pattern (more convergent towards the apex), the smaller number of striae in 10 μm, and lower density of areolae. Nedium sacoense is shorter (60–80 µm) and wider (19–25 µm) and differs by having a straight raphe (not lateral). Moreover, N. sacoense is different from N. muyrakytan by having parallel and radiate striation patterns at the center and a smaller number of longitudinal canals along each valve margin. Neidium muyrakytan can be easily distinguished from N. sterrenburgii by having a noticeable difference in striation pattern, number of striae in 10 μm, shape of the apices, and morphometric dimensions ( Table 3 ).

Figures

FIGURES 19–32. LM valve views. Figs. 19–25. Neidium itapariensis. Fig. 23, holotype. Fig. 22, isotype. Figs. 26–32. Neidium muyrakytan. Fig. 26, holotype. Fig. 29, paratype. Scale bar = 10 μm

FIGURES 33–39. Neidium muyrakytan in SEM. Fig. 33. General external valve view. Figs. 34, 35. External view showing proximal raphe deflected hooks forming bent at approximately 90o. Fig. 36. Triangular lacinia that cover the distal raphe endings. Fig. 37. General internal valve view. Fig. 38. Internally, distal raphe endings showing a prominent thickened nodule. Fig. 39. Proximal raphe endings form loosely interconnected ribbed nodules. Scale bars: Figs. 33, 37 = 10 μm; Figs. 34–36, 38, 39 = 2 μm.