Pseudostaurosira crateri sp. nov. (Fragilariaceae, Bacillariophyta), a new small araphid, fossil diatom species from the Pleistocene (Atlantic Forest, Brazil) Author Marquardt, Gisele C. 0000-0002-2721-1487 Universidade Guarulhos, Centro de Pós-Graduação, Pesquisa e Extensão CEPPE, Praça Tereza Cristina 88, 07023070 Guarulhos, SP, Brazil. & giselecmarquardt @ gmail. com; https: // orcid. org / 0000 - 0002 - 2721 - 1487 giselecmarquardt@gmail.com Author Bicudo, Denise C. 0000-0002-4248-3261 Instituto de Botânica, Department of Ecology, Av. Miguel Estéfano 3687, 04301 - 012 São Paulo, SP, Brazil. & denisecbicudo @ gmail. com; https: // orcid. org / 0000 - 0002 - 4248 - 3261 denisecbicudo@gmail.com Author Bicudo, Carlos E. De M. 0000-0003-4030-9961 Instituto de Botânica, Department of Ecology, Av. Miguel Estéfano 3687, 04301 - 012 São Paulo, SP, Brazil. & cbicudo @ terra. com. br; https: // orcid. org / 0000 - 0003 - 4030 - 9961 cbicudo@terra.com.br Author Ledru, Marie-Pierre 0000-0002-8079-9320 ISEM, Université Montpellier, CNRS, EPHE, IRD, F- 34095, Montpellier, France. & marie-pierre. ledru @ ird. fr; https: // orcid. org / 0000 - 0002 - 8079 - 9320 marie-pierre.ledru@ird.fr Author Ector, Luc 0000-0002-4573-9445 Luxembourg Institute of Science and Technology (LIST), Environmental Research & Innovation (ERIN) Department, 41 rue du Brill, L- 4422 Belvaux, Luxembourg. & luc. ector @ list. lu; https: // orcid. org / 0000 - 0002 - 4573 - 9445 luc.ector@list.lu Author Wetzel, Carlos E. 0000-0001-5330-0494 Luxembourg Institute of Science and Technology (LIST), Environmental Research & Innovation (ERIN) Department, 41 rue du Brill, L- 4422 Belvaux, Luxembourg. & carlos. wetzel @ list. lu; https: // orcid. org / 0000 - 0001 - 5330 - 0494 carlos.wetzel@list.lu text Phytotaxa 2021 2021-04-12 496 2 105 120 http://dx.doi.org/10.11646/phytotaxa.496.2.1 journal article 10.11646/phytotaxa.496.2.1 1179-3163 5423536 Pseudostaurosira crateri Marquardt & C.E.Wetzel , sp. nov. ( Figs 1–57 ) Description :—LM ( Figs 1–47 ): Frustules rectangular in girdle view ( Figs 40–46 ), sometimes forming short chains with two frustules bound together ( Fig. 47 ). Valves isopolar, lanceolate to rhomboid, narrowly rounded to cuneate apices in larger specimens becoming elliptical with broader rounded apices in smaller ones ( Figs 1–39 ). Sternum wide and lanceolate ( Figs 1–39 ). Striae very short, alternate, parallel in the valve center to slightly radiate toward the apices ( Figs 1–47 ). Dimensions (n = 50): length 3.1–16.6 µm; width 2.2–3.2 µm; striae 18–20 in 10 µm. SEM ( Figs 48–57 ): Valve mantle steep with edge parallel to valve face/mantle junction ( Figs 49–52 ). Siliceous plaques absent. Striae uniseriate, uninterrupted from the face to the valve mantle ( Figs 49–57 ), composed of one round to slightly square areolae on the valve face ( Figs 48–51 ) and two to three on the valve mantle ( Figs 49–52 ). Internally, areolae open into a single depression running from valve face to mantle ( Figs 53, 54 ). Inner areolar openings covered with siliceous material depositions on the volae ( Figs 50, 51 ) in the form of two superimposed concentric disks of different diameter ( Figs 54–57 ). Incipient and rudimentary spines occasionally located on raised virgae at the valve face/mantle junction, sometimes two per virgae or even absent ( Figs 51, 52 ). Virgae slightly raised with respect to striae ( Figs 48–51 ). Apical pore fields composed of small poroids placed within cavernous troughs carved deep into the valve present at both apices, more or less developed and positioned at the valve face/mantle junction ( Figs 48–57 ); internal openings arranged in discernible rows ( Figs 53–57 ). Rimoportula absent. Girdle bands composed of several open copulae without perforations ( Fig. 52 ). Valvocopula are wider than other copulae ( Fig. 52 ). Plastids not observed. FIGURES 1–47. LM micrographs of Pseudostaurosira crateri Marquardt & C.E.Wetzel sp. nov. from type material (holotype SP365.548) sampled from Colônia Basin, São Paulo, Brazil. (1–39) Valvar view. (40–47) Frustules in girdle view. Figure 47 shows two neighboring frustules in girdle view. Scale bar 10 µm. Type :— BRAZIL . São Paulo (SP), Parelheiros District : Colônia crater, from 4376– 77 cm depth (~1.4 Ma) in the COL17–3 sediment core, 23°52’ S , 46°42’20” W . 900 m asl , M.-P. Ledru & A.O. Sawakuchi , August 2017 ( holotype : SP!, slide SP365.548, here depicted in Figs 1–57 . The holotype specimen is shown in Fig. 12 . Isotype: BR ! slide BR- 4582) . Etymology :—The Latin name crateri refers to the Colônia Basin geomorphological structure where the sample was collected. Associated flora :— Pseudostaurosira crateri sp. nov. was abundant in the holotype slide (30% relative abundance). The taxon was associated with a high abundance of an unidentified genus (43.2%) followed by Achnanthidium sp. (11%), Aulacoseira ambigua (Grunow) Simonsen (1979: 56) (3.8%), Planothidium sp. (3.7%), and Staurosirella sp. (3.3%). Recent research in São Paulo State reservoirs found that A. ambigua was abundant in colder (winter), slightly acid waters ( Bicudo et al. 2016 ) and correlated to the total nitrogen (NT) vector, as well as the lowest conductivity and Secchi disk values through unimodal-based method based on Detrended Correspondence Analysis (DCA) ( Marquardt et al. 2018 ). Notwithstanding, studies on the identity of co-occurring species and inferences on the ecology of the new species are yet to be developed.