Two new species of Achnanthidium Kützing (Achnanthidiaceae) from the Quaternary sediments of the Colônia basin, Southeast Brazil Author Marquardt, Gisele C. Universidade Federal do Paraná, Departamento de Botânica, Setor de Ciências Biológicas, P. O. Box 19031, 81531 - 980 Curitiba, PR (Brazil) giselecmarquardt @ gmail. com (corresponding author) giselecmarquardt@gmail.com Author Bicudo, Denise C. Instituto de Pesquisas Ambientais, Biodiversity Conservation Department, Avenida Miguel Estéfano 3687, 04301 - 012 São Paulo, SP (Brazil) Author de M. Bicudo, Carlos E. Instituto de Pesquisas Ambientais, Biodiversity Conservation Department, Avenida Miguel Estéfano 3687, 04301 - 012 São Paulo, SP (Brazil) Author Ledru, Marie-Pierre ISEM, Université Montpellier, CNRS, EPHE, IRD, F- 34095 Montpellier (France) Author Wetzel, Carlos E. Luxembourg Institute of Science and Technology, Environmental Research & Innovation Department, 41 rue du Brill, L- 4422 Belvaux (Luxembourg) text Cryptogamie, Algologie 2023 2023-09-27 20 6 111 126 https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/algologie2023v44a6.pdf journal article 10.5252/cryptogamie-algologie2023v44a6 fec7f7bd-731e-4e8e-9be3-6ee703d9c57c 1776-0984 8399144 Achnanthidium ectorianum Marquardt & C.E.Wetzel , sp. nov. ( Figs 1-4 ) HOLOTYPE . — Brazil . São Paulo , SP, Parelheiros District , Colônia crater, 23°52’S , 46°42’20”W , 900 m a.s.l. , from sample 4268- 69 cm liner depth ( c . 1.37 Ma; 4311 composite depth) of the COL17-3 sediment core, VIII.2017 , M.-P. Ledru & A.O. Sawakuchi (SP[ SP365.548 ]!). ISOTYPE . — Same data as holotype ( BR [ BR4582 ]!). TYPE LOCALITY . — Brazil . São Paulo , SP, Parelheiros District, Colônia crater, 23°52’S , 46°42’20”W , 900 m a.s.l. ETYMOLOGY . — The species is dedicated in honor of our mentor, friend, and colleague Luc Ector (1962-2022), who taught us much about Achnanthidium and its features. ECOLOGY AND DISTRIBUTION . — Achnanthidium ectorianum Marquardt & C.E.Wetzel , sp. nov. was frequently observed in the core (11.1% relative abundance). Accompanying taxa included an undetermined diatom genus (43%), Staurosira sp. 1 (20%), Pseudostaurosira crateri Marquardt & C.E.Wetzel (10%), Aulacoseira ambigua (Grunow) Simonsen (3.8%), and Planothidium scrobiculatum Marquardt & C.E.Wetzel (3.7%). DESCRIPTION LM observations ( Fig. 1 ) Frustule in girdle view is narrow, rectangular, and bent with weakly recurved apices ( Fig. 1 AN). Linear-elliptical valves, with almost parallel margins, are very delicate and difficult to observe. Broadly rounded to subrostrate apices ( Fig. 1 A-AM), sometimes slightly curved to the same side ( Fig. 1 I-L); 10.5- 15.5 µm long, 2.5-3.0 µm wide. Raphe valve: very narrow axial area, linear to linear-lanceolate; central area composed of 1-3 shortened striae on both sides of the valve, resembling an X-shape ( Fig. 1 D-G). Raphe filiform, straight. Transapical striae not discernible. Rapheless valve: narrow and linear axial area ( Fig. 1 U-AM). Transapical striae not discernible. The girdle view is narrow, rectangular, and arcuate, with pointed apices faintly curved to the rapheless valve ( Fig. 1 AN). FIG . 2. — Achnanthidium ectorianum Marquardt & C.E.Wetzel , sp. nov. Population from the type locality. SEM: A -E , external views, raphe valve; F , internal view, raphe valve. Scale bars: A, 4 µm; B-F, 5 µm. SEM observations ( Figs 2-4 ) Raphe valve:raphe prolonged after the striae,terminating on the border between the valve face and mantle ( Fig. 2 A-D). Straight central and terminal raphe fissures ( Fig.2 A-E).Striae (30-38) are mainly composed of 2-3,rarely 4,that are rounded areolae,curved close to the apices ( Fig.2 A-E).Internally,proximal raphe endings slightly deflected in opposite directions,distal endings terminating in small helictoglossae( Fig.2F ).Rapheless valve:very narrow axial area, slightly depressed below the valve surface ( Figs 3D, F ; 4C, F ).Striae ( 32-36 in 10 µm) are mainly composed of 2-4 rounded to elongate areolae ( Figs 3 A-F; 4A-C). At times, the areolae fuse forming a slit ( Figs 3A ; 4A, E ). Mantle with one row of slit-like transapically orientated areolae ( Figs 3B, D ; 4 A-C, F).