The Rhodophyta is a relatively well-defined group of about 6,000 algal species with several features that differentiate them from other algal divisions, such as the pres­ence of accessory phycobilin pigments, the absence of flagella and centrioles [36]. The vast majority of red algae are marine multicellular, macroscopic species, which account for the majority of the so-called seaweeds [37]. The main habitats are near­shore and offshore zones (down to 40-60 m) in tropical and temperate climate regions while the presence of accessory pigments allow algae to grow at depths down to 200-250 m. Species with calcified cell walls are important for the estab­lishment and support of coral reef formation. Red algae are also found in brackish and fresh water, as well as in soil [38, 39].

Porphyra species are an important food source for humans in the Asia region [40]. Several Rhodophyta species (Gelidium, Gracilaria) are an important source of agar and agarose [41] . These polysaccharides are used in many laboratories for preparing culture media and separating nucleic acids [42]. Carrageenan is widely used in the food industry as a gel forming substance and stabilizer [43] (Tables 5-7). Structural, biochemical characteristics and productivity of selected red algae species are presented in Tables 5-7.