The synurids (order Synurales) are a small group of heterokont algae, found mostly in freshwater environments, characterized by cells covered in silica scales.
In Synura, these are formed on the surface of the chloroplasts,[3] two of which are usually present, but sometimes only one divided into two lobes is seen.
The cells have two heterokont flagella, inserted parallel to one another at the anterior, whose ultrastructure is a distinguishing characteristic of the group.
They were formally defined as a separate group by Andersen in 1987, who placed them in their own class Synurophyceae, based on an earlier approach of more narrowly defining major lineages of chrysophyte algae by British phycologist David Hibberd.
[8][9] Present classifications include the synurids as an order (Synurales) within Chrysophyceae.