The raphidophytes are a small group of mainly marine genera of phytoplankton. They are single-celled, flagellated, typically range in size from 30-80 um and lack cell walls or scales (i.e., naked flagellates). Raphidophyceae is a class of algae in the Division Chrysophyta, the golden-brown algae.

Heterosigma and Fibrocapsa species have been associated with ‘red tide’ blooms off the coasts of Japan and New England. Fish kills have occasionally been observed related to the species. In Delaware during the year 2000, a fish kill was associated with a toxic bloom of Chattonella cf verruculosa. These genera are being observed in Maryland, however, with no evidence of toxic events to date.