A new order and family of diatoms: Arcanodiscales, Arcanodiscaceae (Bacillariophyta) to accommodate Arcanodiscus platti gen. nov. et sp. nov. from the Argentinian Patagonia

Abstract

A new diatom, Arcanodiscus platti gen. nov. et sp. nov., is described from the Argentinian Patagonia with a novel combination of features. Frustules are robust, strongly silicifi ed, with large and thick central hyaline area and thick valve mantle, under the valve edge often with external parallel undulations. Valves without labiate or strutted processes, the valve mantle areolae internally with otae; a combination of features that has not been described before. The new taxon is morphologically closely related to several representatives of the genus Melosira C.A. Agardh, e.g., M. robusta Hustedt (Houk comm.). However, it diff ers from them by the discoid frustules solitary or forming short fi laments, non-oculate, tubular areolae occluded internally by rotae, lacking of processes, but having a single special round apperture, herein termed the portula. Therefore, a new order and family, Arcanodiscales ord. nov. and Arcanodiscaceae fam. nov., are here described to allocate the genus Arcanodiscus gen. nov. Morphological details of the new species, based on a combined light (LM) and scanning electron (SEM) microscopy, as well as ecological aspects, are discussed in the light of available information.