Achnanthidium ectorianum Marquardt & C.E.Wetzel, 2023

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, Cryptogamie, Algologie 20 (6), pp. 111-126 : 114-115

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).

Figures

FIG. 1. — Achnanthidium ectorianum Marquardt & C.E.Wetzel,sp. nov.Population from the type locality.LM micrographs,size diminution series: A-T, raphe valve; U-AM, raphless valve; AN, frustules in girdle view. Scale bar: 10 μm.

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.

FIG. 3. — Achnanthidium ectorianum Marquardt & C.E.Wetzel, sp. nov. Population from the type locality. SEM: external views, rapheless valve. Scale bars: 5 µm.

FIG. 4. — Achnanthidium ectorianum Marquardt & C.E.Wetzel, sp. nov. Population from the type locality.SEM: A-C, external views, rapheless valve;D-E, internal views, rapheless valve; F, girdle view. Scale bars: A, 3 µm; B-F, 5 µm.