They are autotrophic and heterotrophic. Euglena Golden algae occur as single cells or as colonies of great diversity and complexity. Most are freshwater, a few marine. Some lake dwelling golden algae are both heterotrophic and autotrophic. Brown Algae are all multicellular.
Most brown algae live in the cool waters off the temperate and sub polar areas.
Members of the genus Fucus are good examples. Their algal body is the thallus, a multi cellular structure that looks like a plant but has no vascular tissue. It is attached to the surface of rocks by a structures called a holdfast.