Polarised light micrograph of red algae from the Baltic Sea. Algae is usually differentiated based on pigments; red algae contains the pigment phycoerythrin. It is abundant in marine habitats. Despite its name, red algae can vary in colour from bright green to pink, red and purple. There are approximately 6,000 species of predominantly marine algae, often found attached to other shore plants. Magnification: 93x when printed 10 centimetres wide.