Fallacia fawensis Al–Handal, Al–Shaheen, Al–Saedy & Wulff, 2022

Al-Handal, Adil Y., Al-Shaheen, Maitham A., Al-Saedy, Rehab N. & Wulff, Angela, 2022, Fallacia fawensis sp. nov., a new brackish water diatom (Bacillariophyceae) from Southern Iraq, Phytotaxa 550 (1), pp. 71-78 : 73-75

Fallacia fawensis Al–Handal, Al–Shaheen, Al–Saedy & Wulff sp. nov.

(Figs LM 1–10, SEM 11-19)

Description:

LM observation ( Figs 1–10 ): Cells solitary. Valves are linear lanceolate to elliptical with rounded apices, 7.7–12.3 μm long and 3.5–5.1 μm wide (n=32). Striae are very fine and difficult to resolve in LM. In the larger specimens and in differential interphase contrast (DIC) observation, striae in the middle part of the valve may appear distinctly parallel ( Fig. 10 ). The lateral hyaline areas are indistinct or appear faint in some specimens. The central area is very small, axial area is indistinct. Raphe branches are weakly arched towards the primary side of the valve, proximal raphe endings appear slightly bent.

SEM observation ( Figs 11–19 ): Externally, the valve surface is covered with a porous conopeum which extends from the raphe sterna to shortly before valve mantle ( Figs 11–14 ). The conopeum pores are rounded and arranged in transapical lines which appear mostly equidistant. The valve mantle extends to half the distance between valve margin and raphe canal and possesses very small finger–like protrusions which correspond to a row of areolae under the conopeum (Figs 11,15). Raphe sterna are slightly arched, becoming wider around the proximal endings and slightly raised above valve surface (Figs 11,12,15). Raphe proximal endings are gradually widening towards the central area ( Fig. 15 ). Raphe distal endings are deflected to the same side and extend to the valve mantle, surrounded on both sides by two narrow slits (Figs 12,14 white arrows). Before reaching the valve apex, inner margins of raphe sternum come close to each other leaving a very narrow lacuna–like groove through which raphe is connected to the deflected terminal part of the raphe on the mantle ( Fig. 14 , black arrow). Striae are uniseriate, 26–34 in 10 μm, composed of three longitudinal rows of areolae ( Fig. 12 ). The outer row under the mantle is formed of elongated areolae and the two inner rows are formed of equidistant rounded areolae ( Fig. 12 ). The areolae in the row on both sides of the raphe are terminated before raphe proximal endings leaving a quadrangular central area ( Fig. 15 ). Internally, raphe proximal endings are simple and separated by a slightly elevated and narrow central nodule ( Figs 16–18 ). The distal endings are terminated by a shallow helictoglossae, slightly before valve margin ( Fig.19 ). In all specimens examined, the lateral hyaline areas are not truly hyaline and devoted of striae but are formed of lyrate silica flaps covering the areolae and not connected across the central area ( Figs. 16–18 ). In some specimens, these silica flaps are rather thin where areolae can be seen underneath ( Fig. 18 , arrows). The inner row of areolae adjacent to raphe is formed of rounded areolae (Figs 18,19), while the outer row is formed of thin and elongated areolae ( Fig. 19 ).

Holotype: Permanent slide and material containing frustules of Fallacia fawensis sp. nov., are deposited in the Botanischer Garten, Freie Universität Berlin, Germany under accession B 40 0045360 (holotype is illustrated in Figs 1,10) . Phycobank registration: http://phycobank.org/103157.

Type locality: Faw town, western bank of the Shatt Al–Arab River, Southern Iraq (29 o 58´22´´ N, 48 o 28´14´´ E).

Etymology: The epithet fawensis refers to the Faw town in southern Iraq where this species was first encountered.

Ecology: Fallacia fawensis was a rare epipelic species within the diatom community found on the muddy shores of Shatt Al–Arab River at Faw town, Southern Iraq. Salinity at time of collection was 5.2 and water temperature 38°C. On all slides prepared from the samples, F. fawensis constituted an average of 1.2% of the other taxa and was associated with some common taxa including Entomoneis corrugata (Giffen) Witkowski, Lange –Bertalot & Metzelten (2000:198)(3.75%), Halamphora sp. (4.5%), Nitzschia clausii Hanitzsch (1860: 40) (7.3 %), Nitzschia palea (Kützing) W. Smith (1856:89) (9.5%) and Petrodictyon gemma (Ehrenberg) D.G.Mann (in Round et al. 1990:638) (7.5%). Fallacia fawensis was not encountered in samples collected from northern parts of Shatt Al–Arab River.

Figures

FIGURES 1–10: Fallacia fawensis Al-Handal, Al-Shaheen, Al-Saedy & Wulff sp. nov., LM images of the type material from Shatt Al–Arab River, Southern Iraq showing valve size and outline variation. Scale bar = 10 μm.

FIGURES 11–14: Fallacia fawensis Al-Handal, Al-Shaheen, Al-Saedy & Wulff sp. nov. Figs 11,13 SEM external valve face showing raphe sterna and valve mantle. Fig. 12 SEM upper part of the valve external face exhibiting the narrowing raphe sterna near valve apex (arrow). Fig. 14 SEM detail of the external valve face showing structure of the conopeum and the polar elongated pores of the lyre canal (arrows). Scale bars = 1 μm for Figs 11,13, 0.2 μm for Fig. 12, 0.4 μm for Fig. 14.

FIGURES 15–19: Fallacia fawensis Al-Handal, Al-Shaheen, Al-Saedy & Wulff sp. nov. Fig. 15 SEM middle part of the external valve face showing proximal raphe sterna and endings. Figs 16,17 SEM internal valve face. Fig. 18 SEM internal valve face showing the thin silica flaps covering parts of the elongated striae and appear as lateral areas. Fig. 19 SEM upper part of internal valve face showing distal raphe ending on helictoglossa. Scale bars = 1 μm for Figs 15–18, 0.2 μm for Fig 19.