Desmids are microscopic and can live in thin films of water. Some species even have a strong preference for these thin water films and this is called a (semi) atmophytic lifestyle. These species are resistant to desiccation.
Diatoms are a type of plankton called phytoplankton, the most common of the four plankton types. Another classification divides plankton into eight types based on size: in this scheme, diatoms are a type of microalgae.
Phytoplankton is the base of several aquatic food webs. In a balanced ecosystem, they provide food for a wide range of sea creatures including whales, shrimp, snails, and jellyfish. Phytoplankton, also known as microalgae, are similar to terrestrial plants in that they contain chlorophyll and require sunlight in order to live and grow.