Algae ︎︎︎

Red algae are protists or microscopic organisms in the phylum Rhodophyta, and range from simple one-celled organisms to complex, multi-celled organisms. Of the more than 6,000 species of red algae, most are, not surprisingly, red, reddish, or purplish in color.

All algae get their energy from the sun from photosynthesis, but one thing that distinguishes red algae from other algae is that their cells lack flagella, the long, whiplike outgrowths from cells that are used for locomotion and sometimes serve a sensory function. Also surprisingly, they are not technically plants, although like plants they use chlorophyll for photosynthesis and they have plant-like cell walls.

Red algae are found around the world, from polar waters to the tropics, and are commonly found in tide pools and in coral reefs. They also can survive at greater depths in the ocean than some other algae, because the phycoerythrin's absorption of blue light waves, which penetrate deeper than other light waves do, allows red algae to carry out photosynthesis at a greater depth.

Jennifer Kennedy.  What Are Red Algae? (ThoughtCo, 2020)