Table 5. Comparison of Pseudostaurosira occulta sp. nov. with morphologically similar species within the genus. Features in bold italic font are defining for each taxon. Feature/speciesP. polonica (Witak & Lange-Bertalot) E. Morales & M.B. EdlundP. occulta sp. nov.P. oliveraiana Grana, E. Morales, Maidana & EctorP. subsalina (Hustedt) E. MoralesP. zolitschkae M.L. García, S. Bustos, Maidana & E. MoralesValve dimensions (µm)L: 8-23 W: 3-4L: 6.7-35.6 W: 3.3-3.8L: 19.0-39.5 W: 3.5-5.5L: 10-36 W: 4.0-5.3L: 8.5-28.0 W: 3.5-5.0Stria density (in 10 µm)13-1514-1611-1713-1411-14Valve outline; axial area; virgaeBroadly elliptic, rarely clavate, broadly rounded apices, larger specimens slightly constricted in the middle; lanceolate, at same level as virgae in both external and internal views; wider than striaeLanceolate with subrostrate, squarish, broadly rounded apices; lanceolate, faintly depressed with respect to virgae in external and internal view; wider than striaeLanceolate with subcapitate to cuneate ends; broadly lanceolate, at same level as virgae in both external and internal views; wider than striaeLanceolate with parallel sides and subrostrate apices; linear to narrowly lanceolate, faintly depressed with respect to virgae in external and internal view; wider than striaeLanceolate with subrostrate apices, smaller valves biconvex with cuneate, pointy ends; broadly lanceolate, at the same level as virgae in external view, slightly depressed in internal view; much wider than striaeAreolae; volae; striaeWide, elliptic; well-developed, originating from longer areolar axis, and forming a tight mesh in internal view; rarely formed by more than 3 areolae, larger on valveNarrow, round to elliptic; developed, originating from the inner areolar periphery, forming a tight mesh-like structure visible internally; with up to 4 areolae on valve face and up to 2 on valve mantle, usually larger near valve face/mantle transitionNarrow, elliptic to trapezoid; developed, originating from longer axis of areolae; with up to 3 areolae, larger on valve faceNarrow, round to elliptic; poorly developed, originating from inner areolar periphery and projecting inwards; with up to 5 areolae, decreasing in size towards the axial area, a single larger areolae present on valve mantleNarrow, elliptic to 8-shaped, trapezoid on valve mantle; developed and forming a mesh-like pattern in inner view; with 2 areolae of about the same size on face and mantleSpines; stipules; flapsHollow, with elliptic base, narrower than basal vimen, flattened body with very openly concave sides, spatulate tips with somewhat straight bifurcate projections; present but poorly developed; poorly-developed on valve face and mantleSolid, with elliptic to rectangular base, as wide as basal vimen, cylindrical body with open concave sides, with spatulate tips that bear two lateral projections and serrate borders; incipient, subtending a circular depression on spine body; poorly developed on valve face, well-developed on valve mantle, spatulateSolid, round to elliptic base, as wide as basal vimen, flattened body and tips with an overall inverted trumpet shape, tips bifurcate once or twice; absent; absentSolid, round to elliptic base, as wide as basal vimen, flattened body with somewhat straight but flaring sides and spatulate tip bearing two small lateral projections with serrate borders, with an overall ice cream cone shape; incipient; poorly developedHollow, with round to elliptic base, narrower than basal vimen, with flattened body and typically T-shaped tips; well-developed and lobed; developed on valve mantle, lobedApical pore fields; mantle abvalvar blistersSomewhat developed, with a few, large, round pores, sunken into an irregular depression at the valve apex, internally opening into a small roundish depression; well-developed, apparently not present at apicesDeveloped, externally covered by contorted flaps in external view, internally opening in a single ca. elliptic depression, revealing several rows of round poroids; well-developed, also present at valve apicesSomewhat developed, externally sunken into an elliptic depression at the valve apex, internally opening into a ca. elliptic depression with an elevated central area, and showing several round poroids; developed but absent from apicesSomewhat developed, sitting on a step-like transition between valve face and mantle, externally large roundish pores lie in an irregular depression, internally, the narrow, round pores open into a single roundish depression; developed but present at apicesSmall, externally reduced to large pores with cavernous appearance, internally, small round pores lie in a roundish depression; developed, absent from apicesReferencesMorales & Edlund (2003)This studyGrana et al. (2018)Cejudo-Figueiras et al. (2011)García et al. (2021)

Published as part of Morales, Eduardo A., Wetzel, Carlos E. & Ector, Luc, 2021, New and poorly known " araphid " diatom species (Bacillariophyta) from regions near Lake Titicaca, South America and a discussion on the continued use of morphological characters in " araphid " diatom taxonomy, pp. 23 in PhytoKeys 187 on page 23, DOI: 10.3897/phytokeys.187.73338