Pseudostaurosira crateri Marquardt & C.E.Wetzel, 2021

Marquardt, Gisele C., Bicudo, Denise C., Bicudo, Carlos E. De M., Ledru, Marie-Pierre, Ector, Luc & Wetzel, Carlos E., 2021, Pseudostaurosira crateri sp. nov. (Fragilariaceae, Bacillariophyta), a new small araphid, fossil diatom species from the Pleistocene (Atlantic Forest, Brazil), Phytotaxa 496 (2), pp. 105-120 : 107-108

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.

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.

Figures

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.

FIGURES 48–57. SEM micrographs of Pseudostaurosira crateri Marquardt & C.E.Wetzel sp. nov. from type material (holotype SP365.548) sampled from Colônia Basin, São Paulo, Brazil: (48–51) Overall characteristics of the outer surface of the valve face. Notice an apical pore field on each valve end and striae each composed of one areola on valve face and two to three on mantle (50, 51). Arrow 1 points to the volae in the inner perimeter of the areolae (50). Arrow 2 points to the rudimentary or incipient spines located on the virgae (50–52). Girdle view of a frustule showing characteristics of the cingulum. Notice (arrow 3) open girdle bands (52). Detail of the areolae open into a single depression (arrow 4) running from valve face to mantle (53). Inner valve surface showing absence of rimoportulae and areolae characteristics (55–57). Notice internal detail (arrow 5) of superimposed disks formed by depositions of siliceous material on the volae (57). Detail (arrow 6) of apical pore field (57).