They are a group of universally distributed, rigid, essentially unicellular, microscopic organisms lacking chlorophyll.
(They; are; a group of universally distributed, rigid, essentially unicellular, microscopic organisms) (universally distributed, rigid, essentially unicellular, microscopic organisms; lacking; chlorophyll)
They universally distributed, rigid, essentially unicellular, microscopic organisms
are lacking
a group of universally distributed, rigid, essentially unicellular, microscopic organisms
chlorophyll