Schizocladia ischiensis: a new filamentous marine chromophyte belonging to a new class, Schizocladiophyceae.

A new marine filamentous chromophyte Schizocladia ischiensis sp. nov. is described from Naples, Italy, and a new class, Schizocladiophyceae, is proposed to accommodate the species based on morphology, photosynthetic pigment analysis, and rbcL and 18S rRNA gene sequences. The vegetative thallus is composed of branched filaments, 3-7 microm in diameter, containing one to two light brown parietal plastids. Cell walls are composed of layered fibers containing alginates, but lacking cellulose. Plastids are of the typical chromophyte type, containing chlorophylls a and c, and abundant fucoxanthin. Zoospores are formed by direct transformation of vegetative cells or through a process including a multinucleated cell stage. Zoospores are teardrop-shaped with a longer anterior flagellum with tubular mastigonemes and a shorter smooth posterior flagellum with a basal swelling. Flagella have a single basal plate and multi-gyred transitional helix distal to the basal plate. Each zoospore has an eyespot. Phylogenetic analyses using rbcL and 18S rDNA sequences suggest the closest phylogenetic relationship with Phaeophyceae, and then with Xanthophyceae and Phaeothamniophyceae. Nevertheless, Schizocladia differs from Phaeophyceae in some essential features (i.e. cell wall lacking cellulose and plasmodesmata, presence of flagellar transitional helix). Therefore, an independent class Schizocladiophyceae is proposed to accommodate this new taxon.