Encyonema capixabense Marquardt, Morais & Zorzal-Almeida, 2025

Marquardt, Gisele C., Morais, Krysna S., Costa, Beatriz C., Fernandes, Valéria O. & Zorzal-Almeida, Stéfano, 2025, Encyonema capixabense sp. nov. (Cymbellales, Bacillariophyceae): a widespread diatom in Brazilian rivers first described from the Rio Doce Basin (southeastern Brazil), Phytotaxa 708 (1), pp. 77-86 : 79-81

Encyonema capixabense Marquardt, Morais & Zorzal-Almeida , sp. nov. ( Figs 1–46 )

LM observations ( Figs 1–36 ):—Valves strongly dorsiventral, semi-lanceolate. Dorsal margin convex. Ventral margin slightly tumid at the medium region. Valve apices rounded, rostrate to subcapitate, deflected to the ventral side. Length 15–20 μm, width 4–5.5 μm, Maximum L:W= 3.9. Axial area narrow, strongly displaced ventrally. Central area absent. Dorsal striae moderately radiate at the valve centre, 11–12 (13) in 10 μm and radiate to the apices. Ventral striae very short, moderately radiate at the valve centre, convergent to the ends. Areolae 36 in 10 μm. Raphe filiform, eccentric. Proximal raphe endings short, slightly widened, directed towards the dorsal side. Terminal raphe endings bent towards the ventral side. Dorsal stigmoid not clear.

SEM observations ( Figs 37–46 ):—External valve view ( Figs 37–42 ): striae extend from the axial area to the mantle and are composed of individual transapically elongated, slit-like areolae ( Figs 38–42 ), numbering 36 in 10 µm ( Figs 38–42 ). Mantle perforated by small linear poroids at the valve ends ( Figs 37, 38, 42 ). Proximal raphe endings curved towards the dorsal margins, pore like and slightly expanded ( Figs 37–40 ). Distal raphe endings curving over the junction of the valve face and mantle ( Figs 37, 38, 42 ). Small rounded stigmoid located at the end of dorsal central striae ( Figs 37–41 ). Internal valve view ( Figs 43–46 ): striae separated by well-developed virgae ( Figs 43–46 ). Areolae separated by siliceous struts ( Figs 43–46 ). Raphe slits straight ( Figs 43–46 ). Distal raphe endings terminate in small helictoglossae which are slightly angled towards the ventral margin ( Figs 43, 46 ), proximal raphe endings lacking an intermissio ( Figs 44, 46 ). Stigmoid is a vertical elongated slit at the end of dorsal central striae ( Figs 44, 46 ).

Type:— BRAZIL. Espírito Santo (ES): Linhares District, Rio Doce , periphyton, 0 m a.s.l., 19°24’24.07” S, 40°4’14.65” W, 1 November 2018, leg. S. Zorzal-Almeida (holotype: slide VIES! Microalga 9800014, depicted in Fig. 04; isotype: slide UPCB! 1152) .

Etymology:— The specific epithet capixabense is derived from capixaba, a demonym referring to the state of Espírito Santo, Brazil, where the species was sampled.

Associated flora:— Encyonema capixabense sp. nov. was the most abundant diatom in the holotype slide (30.9% of relative abundance). The taxon was associated with a high abundance of Achnanthidium sp. 1 (20.6%) and Gomphonema lagenula Kützing (8.7%).

Ecology:— The holotype was collected attached to a submerged plant substrate ( Apocynaceae ) in a lotic environment. Encyonema capixabense sp. nov. was recorded in lotic environments of the lower Rio Doce region, where it exhibited an average relative abundance of 6.8%, reaching a maximum of 47.3%. In lentic environments, its maximum abundance was 5.8%, with an average of 0.3%. The species demonstrates a preference for mesotrophic conditions (ecological optimum for total phosphorus = 57.1 µg L⁻¹; electrical conductivity = 84.2 µS cm⁻¹), with a pH of approximately 7.7 and a turbidity of 38.9 NTU (Nephelometric Turbidity Unit).

Figures

FIGURES 1–36. LM micrographs of Encyonema capixabense Marquardt, Morais & Zorzal-Almeida, sp. nov. from type material (holotype VIES! Microalga 9800014, depicted in Fig. 04) sampled from Rio Doce, Espírito Santo, Brazil. Valve view. Fig 21—Valve in phase contrast. Scale bar 10 µm.

FIGURES 37–46. SEM micrographs of Encyonema capixabense Marquardt, Morais & Zorzal-Almeida, sp. nov. from type material (VIES! Microalga 9800014) sampled from Rio Doce, Espírito Santo, Brazil: SEM external views (Figs 37–42): Overall characteristics of the outer surface of the valve face. Detail of small stigmoid located at the end of the median striae (Figs 39–41). SEM internal views (Figs 43–46): Inner valve surface characteristics. Notice raphe distal end (42). Notice internal detail of helictoglossae (Fig. 43), virgae and struts (Figs 44, 45). Detail of small stigmoid located at the end of the median striae (Figs 44–46). Scale bar: Figs 39, 42, 43= 1 µm; Figs 41, 45= 500 nm; Figs 40, 44= 2 µm; Figs 37, 38, 46= 5 µm.