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Abstract
Abstract The study of the genus Melosira in plankton samples from the lower Iguaçu River revealed the presence of four taxa: Melosira undulata (Ehrenberg) Kützing var. undulata, M. undulata var. normanni Arnott, M. varians C. Agardh and M. muscigena Iwahashi. We present illustrations of the frustules using light microscopy (LM), descriptions, and comments about the morphology of the four taxa. The analysis of Melosira muscigena under scanning electron microscopy revealed unprecedented details of the ultrastructure, such as the shape and distribution of the rimoportulae at the valve mantle. This is the first record of Melosira undulata var. undulata and the second of M. muscigena in Brazil.
Highlights
IntroductionAgardh are characterized by cylindrical to subspherical frustule, usually united at the valve faces by mucilage pads and small irregular spines (Crawford 1975) in pairs or chains of three cells (Van Heurck 1896)
Rimoportulae scattered on the valve face and disposed in a ring around the mantle, not equidistant from each other
Our study found a smaller number of areolae (12‒14 in 10 μm) in the var. normanii compared to the typical variety (17‒18 in 10 μm)
Summary
Agardh are characterized by cylindrical to subspherical frustule, usually united at the valve faces by mucilage pads and small irregular spines (Crawford 1975) in pairs or chains of three cells (Van Heurck 1896). The valve face can be flat or convex and may be bordered by a corona, with granules more or less developed, and a carina (collar-like structure) (Crawford 1975). The areolae are loculated with loculi open to the outside through small pores. The cingulum presents ligulate bands perforated by longitudinal rows of small pores (Round et al 1990). Rimoportulae usually occur near the edge, scattered or grouped at the valve mantle (Round et al 1990)
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