= Red algae Circumscription: The red algae, unicellular to multicellular (up to 1 m) mostly free-living but some parasitic or symbiotic, with chloroplasts containing phycobilins. Cell walls made of cellulose with mucopolysaccharides penetrated in many red algae by pores partially blocked by proteins (complex referred to as pit connections). Usually with separated phases of vegetative growth and sexual reproduction. Common and widespread, ecologically important, economically important (source of agar). No flagella. Ultrastructural identity: Mitochondria with flat cristae, sometimes associated with forming faces of dictyosomes. Thylakoids single, with phycobilisomes, plastids with peripheral thylakoid. During mitosis, nuclear envelope mostly remains intact but some microtubules of spindle extend from noncentriolar polar bodies through polar gaps in the nuclear envelope. Synapomorphy: No clear-cut feature available; possibly pit connections Composition: About 4,000 species.