Abstract
A revised texonomic description of Phaeodactylum tricornutum Bohlin is presented, with special emphasis on the details of the silica valve, a structure hitherto unobserved. The features distinguishing P. tricornutum from Nitzschia closterium (Ehr.) W. Sm., with which it has frequently been confused, are summarized. In view of the unique characters of P. tricornutum, it is proposed to establish within the Bacillariales a new suborder, the PHAEODACTYLINEAE to which Phaeodactylum is assigned as the only known genus.
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