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Abstract
The centric diatom Thalassiosira rudis sp. nov. has been described by morphological and ultrastructural analyses of the frustules using light and scanning electron microscopy. The species was found in the freshwater ecosystems from Brazil. T. rudis is characterized by a convex valve face sunken in the middle and downturned at mantle, wider central areolae, internal opening of cribra branched in dichotomic rows, absence of central processes, 1–3 marginal rimoportulae, presence of marginal ring of fultoportulae with inward extension furnished with cowlings and very short external tube, cingulum composed of four or more open bands, singly and alternately septate, and valvocopulae with one row of larger poroids. The new species was compared morphologically with closely related species ofThalassiosirasuch as T. gracilis (Karsten) Hustedt, T. visurgis Hustedt and T. rudolfii (Bachman) Hasle. Comments about T. weissflogii (Grunow) Fryxell & Hasle and T. leptopus (Grunow) Hasle & Fryxell were presented.
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