Nitzschia sigma (Kützing) W. Smith (1853: 39)

Al-Handal, Adil Y., Thomas, Evan W. & Pennesi, Chiara, 2018, Marine benthic diatoms in the newly discovered coral reefs, off Basra coast, Southern Iraq, Phytotaxa 372 (2), pp. 111-152 : 139

Nitzschia sigma (Kützing) W. Smith (1853: 39) ( Fig. 95 )

References: Krammer & Large-Bertalot 1988, p. 32, pl. 23, figs 1–9; Witkowski et al. 2000, p. 404, pl. 206, figs 1–10; Hein et al. 2008, pl. 60, fig. 3.

Features: Length 90–130 μm, width 6–12 μm, fibulae 8–12 in 10 μm, striae 22–28 in 10 μm.

Description: valves linear to linear lanceolate, slightly sigmoid, with curving acute apices. Raphe eccentric, fibulae small, equally spaced.

Remarks: Several varieties of N. sigma were described based on striae density and whether valves (in valve view) are sigmoid or straight. It is sometimes difficult to identify these varieties and some of them might belong to a different species, which requires further investigation of this complex using SEM diagnosis or molecular data. Striae density is rather variable and in some specimens, these are hardly counted under light microscope.

Ecology and Distribution: A widely distributed species in marine and brackish water habitats. Previously reported from the Gulf ( Hendey 1970, Al-Yamani & Saburova 2011, Al-Handal 2011). Common in Basra corals.

Figures

FIGURES 91–102. Marine benthic diatoms in coral reefs off Basra. Fig. 91. Nitzschia behrei, Fig. 92. Nitzschia distans, Fig. 93. Nitzschia fluminensis, Fig. 94. Nitzschia lorenziana, Fig. 95. Nitzschia sigma, Fig. 96. Nitzschia sp., 97. Pssamodictyon panduriformis Fig. 98. Tryblionella coarctata, Fig. 99. Tryblionella didyma, Fig. 100. Tryblionella nicobarica, Fig., Fig. 101. Amphiprora sulcata, Fig. 102. Auricula intermedia.