Abstract.- Resource use and phylogeny are often correlated with morphological variation. Moreover, because biological shapes are often complex and evolve depending on several internal constraints, they must be assessed using integrative methods.

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.