Freshwater

• AlgaeBase Main Page
  • Taxonomy Browser
• AlgalWeb: Web Key for Freshwater Algal Flora of the British Isles
• Freshwater Phytoplankton by PlantBio co., ltd. (in Japanese)
• Index Nominum Algarum Bibliographia Phycologica Universalis
• Japanese Protist Information Server (original Japanese link here)
• University of New Hampshire's PhycoKey
• AlgaeVision (database and virtual collection of images of freshwater and terrestrial algae colleted in Britain and Ireland)

Marine

• AlgaeBase Main Page
• Barents Sea Phytoplankton Taxonomy Table (translated by Google)
• CATALOGUE OF THE BENTHIC MARINE ALGAE OF THE INDIAN OCEAN
• NOAA Taxonomic List of Plankton of Arctic Seas
  • Phytoplankton Main Page
    • Alphabetical List of Phytoplankton Taxa
  • Zooplankton Main Page
    • Alphabetical List of Zooplankton Taxa
• WoRMS Taxon Search

Mixed

• ANSP Algae Image Database
• AQUASCOPE (Tjärnö Marine Biological Laboratory, Strömstad, Sweden)
  • Systematically Ordered Organisms in AQUASCOPE
• Census of Australian Marine Dinoflagellates
• MICROBIAL CULTURE COLLECTION at the National Institute for Environmental Studies in Japan
  • Protist Information Server - Japanese Site in English, multiple division images
• University of New Hampshire's PhycoKey