a division of algae; red algae.
The red algae include unicellular and multicellular forms. All are characterized by the presence in the chromatophores (in addition to chlorophyll a, carotene, and xanthophyll) of chlorophyll d, R-phycoerythrin (a red pigment), and R-phycocyan (a blue-green pigment); by the absence of motile flagellate stages (zoospores and spermatozoa); and by a unique sexual process. The thalli are filamentous, bushy, or lamellar; in some, they are divided into stems and leaflike organs. In a number of species, the thalli are hardened because of calcium deposits (Lithothamnion). The color of the red algae varies from dark red (almost black) to pink, yellowish, and, (occasionally) steel blue. Reserve nutrients include red-algal starch, floridoside, and mannoglycer-ate.
The division Rhodophyta comprises 600 genera (3,750 species). It is divided into two classes: Bangiophyceae and Florido-phyceae. Asexual reproduction proceeds by means of nonmotile spores, which form in sporangia singly (monospores) or in groups of four (tetraspores). Sexual reproduction proceeds by the process of oogamy. Nonmotile gametes, called spermatia, form in the male sex organs, or spermatangia. The spermatia are carried in the water to the female sex organs, or carpogonia. After fertilization, the contents of the carpogonium, in the Bangiophyceae, break up into haploid carpospores; in the Floridophyceae, the carpogonium yields filamentous multicellular processes, on each end of which forms a carpospore. Alternatively, threads emerge from the carpogonium that join together with special large (auxiliary) cells of the thallus, to which are transferred the nuclei that form during the division of the fertilized egg of the carpogonium (one to each). The nuclei within the auxiliary cells do not merge; these cells, in turn, yield filamentous processes bearing carpospores.
Rhodophyta are predominantly marine, often flourishing at greater depths than green and brown algae, owing to the presence of phycoerythrin, which is apparently capable of utilizing green and blue light rays (which penetrate deeper in water than others) for photosynthesis. Less often, the red algae are found in fresh waters and soil. Fossil Rhodophyta have been found in Cretaceous deposits. Ahnfeltia, Gelidium, Phyllophora, and Fur-cellaria are of the greatest practical value, yielding jelling substances (agar, agaroid, and carrageenin). Some members of the group, such as Porphyra, are used as food.
IU. E. PETROV