Fragilaria irregularis Chudaev, Jüttner & Van de Vijver, 2021

Chudaev, Dmitry, Jüttner, Ingrid & Vijver, Bart Van De, 2021, Fragilaria irregularis sp. nov. a new araphid species (Fragilariaceae, Bacillariophyta) from the River Adegoy, Krasnodar Territory, Russia, Phytotaxa 508 (2), pp. 221-228 : 222-223

Fragilaria irregularis Chudaev, Jüttner & Van de Vijver , sp. nov. ( Figs 1–56 )

Description:—LM ( Figs 1–48 ): Cells solitary, ribbon-like colonies not observed. Valves linear in larger and mediumsized specimens to linear-elliptic in smaller specimens. Valve margins tapering abruptly forming well developed ‘shoulders’ near the apices. Apices distinctly protracted, subcapitate. Valve margins sometimes slightly irregular, often with different curvature on both sides of the valve, resulting in an asymmetrical valve shape with a margin slightly more arched on one side and a straight margin on the opposite side. Valve dimensions (n=50): length 14–27 µm, width 3.5–5.5 µm. Sternum distinct although very narrow, linear, not widening in the central part of the valve. Central area absent. Striae alternating, parallel throughout most of the valve, becoming radiate close to apices, irregularly spaced with some virgae much wider than striae, 7–14 in 10 µm. Occasionally, striae slightly shortened ( Figs 1, 4, 9, 13, 14, 42, 47 ). Valves showing a more regular striation pattern rare ( Figs 12, 28, 34, 44 ). Areolae not discernible in LM.

SEM ( Figs 49–56 ): Valve surface almost flat. Spines or spine vestiges not observed ( Figs 49–50 , 54, 55 ). Large mantle plaques visible at mantle edge ( Fig. 55 , white arrow). Striae uniseriate, composed of small, circular, usually rimmed areolae; 49–63 areolae in 10 µm ( Figs 49–50 , 54–56 ). One transapically elongated rimoportula present at one apex, replacing part of the last stria ( Figs 49–52 , white arrowheads, 55–56, black arrowheads). Apical pore fields composed of several rows of very small poroids ( Figs 56 , white arrow). Internally, virgae not or only weakly raised above the areolae, the latter present in very shallow grooves. Rimoportula straight to oblique, forming a transapically elongate, lipped slit ( Figs 51–52 , white arrowheads). Cingulum composed of at least two open copulae bearing one row of circular perforations ( Fig. 53 , white arrow) at the junction of pars interior and pars exterior. Most abvalvar copula ligulate ( Fig. 56 , white arrowhead), valvocopula lacking ligula ( Figs 53–56 ).

Type:— RUSSIA. Krasnodar Territory: Adegoy River, vicinity of Afonka Khutor , on mosses, 44.72580° N, 37.93992° E, 176 m asl, D. A . Chudaev , 27th May 2016 (Holotype: MW-D! slide 501s1 = Fig. 7 ; isotypes: slides LE A0000300 , LE A0000303 ) .

Etymology:—The specific epithet refers to the irregular striation pattern.

Ecology and distribution:—The species is so far only known from its type locality, the Adegoy River, where it was present at a relative abundance of 6.5%. The associated diatom flora in the sample was composed of several, at present unidentified, species in Achnanthidium Kützing (1844: 75 , 40%) and Encyonopsis Krammer (1997: 156 , 3%), Diatoma moniliformis ( Kützing 1834: 580) D.M. Williams (2012: 260 , 11%), Gomphonella olivacea ( Hornemann 1810: fasc. 24, pl. 1429) Rabenhorst (1853: 61, 3%), Gomphonema tergestinum (Grunow in Van Heurck 1880: pl. 25, fig. 40) Fricke in A. Schmidt (1902: pl. 234, figs 39–43, 5%), Navicula cryptotenella Lange-Bertalot in Krammer & Lange-Bertalot (1985: 62, 3%) and Nitzschia media Hantzsch (1860: 40 , 6%).

Figures

FIGURES 1–48. Fragilaria irregularis sp. nov., LM, type material, slide MW-D 501s1, Fig. 7 represents the holotype. Scale bar = 10 µm.

FIGURES 49–52. Fragilaria irregularis sp. nov., SEM, type material, sample MW-D 501. 49–50. External view of entire valves. 51–52. Internal view of entire valves. White arrowheads mark rimoportulae. Scale bars = 2 µm.

FIGURES 53–56. Fragilaria irregularis sp. nov., SEM, tilted at 45°, type material, sample MW-D 501. 53. Internal view of valve with attached valvocopula. White arrow marks single row of perforations through valvocopula. 54. External view of an entire frustule. 55–56. Details of the apex of the frustule depicted in Fig. 54. 55. White arrow marks mantle plague, black arrowhead—rimoportula. 56. White arrow marks apical pore field, white arrowhead—ligula, black arrowhead—rimoportula. Scale bars = 2 µm (Fig. 53), 5 µm (Fig. 54), 1 µm (Figs 55–56).