Marine benthic diatoms in the newly discovered coral reefs, off Basra coast, Southern Iraq Author Al-Handal, Adil Y. Department of Biological and Environmental Sciences, University of Gothenburg, Sweden Author Thomas, Evan W. Biology Department, Waubonsee Community College, Sugar Grove, Illinois, USA Author Pennesi, Chiara Department of Life and Environmental Sciences, Polytechnic University of Marche, Ancona, Italia text Phytotaxa 2018 2018-10-12 372 2 111 152 http://dx.doi.org/10.11646/phytotaxa.372.2.1 journal article 10.11646/phytotaxa.372.2.1 1179-3163 13728822 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.