STUDIES ON THE DIATOM UROSOLENIA ROUND & CRAWFORD (RHIZOSOLENIOPHYCIDEAE) PART 1. NEW AND RE-CLASSIFIED SPECIES FROM SUBTROPICAL AND TROPICAL FRESHWATERS

Abstract

Populations of the delicate planktonie freshwater centric diatom genus Urosolenia from several lentic freshwater environments in Africa, Asia, Australia and South America were studied with both LM and SEM. The classical morphological features, e.g. frustule size, shape of the valve, length and positioning of the process and number of girdle bands per unit length, were re-evaluated and additional previously overlooked valve structures were identified as useful for species differentiation. Although fine resolution LM revealed the most important elements of the spine-like process, the SEM showed additional ultrastructural features on the frustule surface and terminal ends as well as structures on the valve margins not resolved in detail by LM. A few new morphological terms are proposed mainly for terminal ends of the process (ligula, seta), the process shaft (poroids, protrusions, ribs) and the valve margin. Using these LM and SEM observations, the genus description is emended and two species previously described earlier under Rhizosolenia are transferred into the recently established genus Urosolenia (U. victoriae (Schroeder) Kling & Rott comb. nov. from Lake Victoria Africa and U. brauni (Hustedt) Rott & Kling comb. nov. from Jurucui Brasil). Three new Urosolenia species are described, two from Australia (U. brevispinosa Kling, McGregor & Rott sp. nov., U. parva Kling, Rott & McGregor sp. nov.), and one from Sri Lanka (U. diademata Rott & Kling sp. nov.). Type localities including ecological data of the environments are listed and a key for identification of the named species is given.