Pseudo-nitzschia mannii

From Amato and Montresor 2008: Cells are linear in valve view and form stepped colonies. Transapical axis length is 1.7–2.6 microns. In the central part, fibulae are more widely spaced and form a larger interspace. Thirty to forty striae and 17–25 fibulae are present in 10 microns. Each stria contains one row of square-round poroids. Poroid density ranges 4–6 per micron, and 3.6% of poroids show a central sector. The cingulum is composed of three open bands. The valvocopula shows 3–4 poroid-high biseriate striae. The second and the third band show biseriate striae.

Molecular data and mating experiments support the recent speciation of P. mannii and P. calliantha (Amato and Montresor 2008).

P. mannii is indistinguishable from P. calliantha, P. caciantha, P. pseudodelicatissima and P. cuspidata using light microscopy (Amato and Montresor 2008). Using electron microscopy, one can distinguish P. mannii by the poroid density and arrangement and the number of sectors in the poroid hymen. Even while using EM, P. mannii can be difficult to distinguish from P. calliantha and P. caciantha.

Trees built with ITS sequences support sisterhood with P. calliantha (Amato and Montresor 2008). The 5.8S regions were identical in P. mannii and P. calliantha. LSU, ITS and rbcL data support the separation of P. mannii and calliantha, however they are very closely related species.

Sexual reproduction has been observed in P. mannii in culture (Amato and Montresor 2008). The process took about 4-5 days to complete. Gamete formation was observed after 48 hours from mixing strains of opposite mating types. Two identical anisogamous gametes are produced per gametangium. Crosses were performed between strains of P. mannii and P. calliantha which resulted in gametogenesis and the production of zygotes, but no viable progeny (Amato et al. 2007).