Some produce nerve poisons toxic to vertebrates. Most members of this group live in fresh water, being especially abundant in polluted habitats. Many euglenoids contain two flagella and contain a hard pellicle made of protein just under the plasma membrane. Their chloroplasts contain chlorophyll a and b and carotenoids. Many contain a red eyespot , which is thought to be used as a photoreceptor.
Euglenoids reproduce asexually by dividing lengthwise into two.
They do not reproduce sexually. Diatoms Diatoms are probably the most abundant aquatic eukaryotes in number of individuals and species. They live singly or in simple filaments or colonies, they occur in either type of aquatic environment. They reproduce sexually and are basically non motile. Most unicellular algae are haploid but diatoms are diploid.