Abstract
Three needle-shaped Ulnaria species are studied using light and scanning electron microscopy. One is identified as Ulnaria acus (Kützing) Aboal and two are proposed as new: Ulnaria rhombus sp. nov. and Ulnaria wulingensis sp. nov. These three species have many common characters: needle-shaped valve outline, ghost striae, a central area circumscribed by shortened striae composed of one or a few areolae, a closing plate composed of a solid plate with some struts connecting the areola wall, and characteristic virgae-vimines structure. Ulnaria acus and U. wulingensis have almost parallel central area margins whereas U. rhombus never has parallel central area margins. Ulnaria wulingensis and U. rhombus (excluding few very small specimens) possess distinctive parallel distal regions of variable length, between 3 and 40 µm, but U. acus only has parallel distal regions in a few, very long specimens. Comparison with similar Ulnaria taxa was carried out and the distinguishing characteristics are summarized. All three species were found in alkaline freshwater (pH 8.3–8.5) with low-moderate conductivity (109.2–286.4 µS/cm).
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