stentor amethystinus stentor amethystinus stentor amethystinus is a single-celled eukaryote. it is often 1.0 millimetre (0.04 in) long and is found in freshwater ponds and lakes. algae live in symbiosis with stentor amethystinus, providing food for the ciliate, which then protects the algae. unlike many of its relatives, stentor amethystinus is red-violet in color, due to the chemical amethystin. the chemical amethystin is structurally similar to the chemical stentorin, which belongs to stentor coeruleus. stentor amethystinus scientific classification domain: eukaryota clade: diaphoretickes clade: sar clade: alveolata phylum: ciliophora class: heterotrichea order: heterotrichida family: stentoridae genus: stentor species: s. amethystinus binomial name stentor amethystinusleidy, 1880