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Cyanidium caldarium (Tilden) Geitler (Cyanidiaceae, Cyanidiophyceae) new record for the Spanish continental algal flora Palabras clave. Cyanidiophyceae, Cyanidium, cuevas, aguas termales, material yesífero, distribución. Keywords. Cyanidiophyceae, Cyanidium, caves, thermal springs, gypsum, distribution.

Phototaxis of 2 cyanidiaceae, Cyanidioschyzon merolae and Cyanidium caldarium, was studied by population experiments. We found that cells of both C. merolae and C. caldarium moved towards light in liquid medium, but that the degree of migration was quite different. When laterally illuminated, most of the C. merolae cells moved towards light at a velocity of 0.27 mm/h. In contrast, only a small proportion of C. caldarium cells showed migration towards light and most of the cells remained dispersed. The exterior cell surface of C. merolae was observed by scanning electron microscopy. It appeared thick and flexible enough to enable crawling movement.

Thermoacidophilic algae (Cyanidiaceae) constitute a taxonomic group with interesting phylogenetic and ecological implications. In this report, we have classified three thermoacidophilic microalgal isolates from Rio Tinto (Spain) using a combination of classical analysis of phenotypic features and the characterization of their electrophoretically determined karyotypes by means of pulsed-field gel electrophoresis. Using this technique, we have been able to demonstrate that thermoacidophilic algae genomes have the smallest genomes of all photosynthetic eukaryotes studied so far. In addition, we show that two of these Rio Tinto isolates may constitute new species within the genus Galdieria.

Treatises on extremophiles are frequently focused on organisms belonging to the Archaea and Eubacteria kingdoms. However, a significant number of eukaryotes, both unicellular and multicellular, have evolved to live and thrive in extreme environments. Although less is known about eukaryotic life in extreme environments in comparison to prokaryotic extremophiles, advances in genomics and in comprehensive, high-throughput metabolic profiling techniques have provided new insight into the metabolic adaptations of eukaryotes living under extreme conditions. In this review, we will provide an overview of extremophilic life forms with emphasis on eukaryotes and we will compare metabolic adaptations in different eukaryotic extremophiles to identify generalities and specializations in adaptation to life under extreme conditions. Special emphasis will be devoted to the thermoacidophilic unicellular red alga Galdieria sulphuraria (Cyanidiaceae) as one example of a eukaryotic extremophile.

The authors carry out a systematic revision of three unicellular eucaryotic algae, often living in mixed population in thermal acidic environment. Such algae were often confused under the binomium Cyanidium caldarium. The authors state that the following specific binomia are to be attributed to the three algae: Galdieria sulphuraria (Galdieri) Merola comb. nova; Cyanidium caldarium Geitler non (Tilden) Geitler emend.; Cyanidioschyzon merolae De Luca, Taddei & Varano. The family Galdieriaceae is instituted for the first of these algae, whereas the other two algae are included in the family Cyanidiaceae Geitler emend. The class Cyanidiophyceae Merola, a new class of the Rhodophyta, is instituted for these two families.