What multicellular forms of life evolved from the early single-celled organisms

Three marine habitats that would have the least access to phytoplankton are,

The three habitats of the deep sea floor: vents and seeps, trenches and seamounts. Phytoplankton thrives in area exposed to sunlight taking up dissolved elements from seawater, including carbon dioxide, to create new cells and are responsible for around half of the planet's photosynthesis and oxygen production. It is primarily found on the surface and lands on the deep sea floor as dead cells, still carrying carbon dioxide, retaining the balance of oxygen/carbon dioxide in the ecosystem.