RED ALGAE

members of the division Rhodophyta (about 3,000 species), predominantly marine algae often found attached to other plants near tropical and subtropical shores. Their morphological range, though not so extensive as that of the brown algae, includes filamentous, branched, feathered, and sheetlike thalli. Thin protoplasmic connections provide continuity between cells. Their usual red or blue colour is the result of a masking of chlorophyll by the phycobilin pigments (phycoerythrin and phycocyanin). The reproductive bodies of red algae are nonmotile. The female sex organ, called a carpogonium, consists of a uninucleate region that functions as the egg and a trichogyne, or projection, that acts as the sperm receptacle. Nonmotile male gametes (spermatia) are produced singly in the male sex organ, the spermatangium. Red algae are important food plants (e.g., laver, dulse) and retain both their colour and gelatinous nature when cooked. Industrially, Irish moss (Chondrus) is used as a gelatin substitute in puddings, toothpaste, ice cream, and preserves. Some species of Corallina are important, along with animal corals, in forming coral reefs and islands. Agar, an amorphous gelatin-like substance prepared primarily from Gracilaria and Gelidium species, is important as a culture medium for bacteria and fungi.