Achnanthidium ectorianum Marquardt & C. E. Wetzel 2023, sp. nov.
Creators: name: Marquardt, Gisele C.
name: Bicudo, Denise C.
name: de M. Bicudo, Carlos E.
name: Ledru, Marie-Pierre
name: Wetzel, Carlos E.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Chromista
Bacillariophyta
Bacillariophyceae
Achnanthales
Achnanthidiaceae
Achnanthidium
Achnanthidium ectorianum

description: 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).
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).
description: Published as part of Marquardt, Gisele C., Bicudo, Denise C., de M. Bicudo, Carlos E., Ledru, Marie-Pierre & Wetzel, Carlos E., 2023, Two new species of Achnanthidium Kützing (Achnanthidiaceae) from the Quaternary sediments of the Colônia basin, Southeast Brazil, pp. 111-126 in Cryptogamie, Algologie 20 (6) on pages 114-115, DOI: 10.5252/cryptogamie-algologie2023v44a6, http://zenodo.org/record/8399144