The sea anemone Anemonia viridis is one of the most common species of the North Aegean Sea. The variety in colour morphs exhibited by this species, causes problems to taxonomy and ecology, and suggests that A. viridis should be subdivided into two distinct species according to the colour of the individuals. The approach used in this study was based on the biometrical cnidae characteristics of the two colour morphs (rustica and smaragdina), as it is known that cnidae biometry has been used as a taxonomic tool for the phylum Cnidaria. More than 20,000 nematocysts were measured to try and find a correlation between these measurements and some body parameters indicative of the maturity grade of the individuals, as potential taxonomic characteristics. Stable cnidae characteristics of the two different colour morphs were compared. However, they differed only in the biometry of the tentacles' a-basitrichs. This slight difference does not support the proposal to subdivide Anemonia viridis into two different species.