Nephroselmis astigmaticasp. nov. is described based on light and electron microscope observations of cultured material, originally collected and isolated from the Natal South Coast, Republic of South Africa. It is characterized by (1) large cell size, (2) absence of a stigma, (3) markedly differentiated anterior part of the cell, (4) possessing two types of flagellar scales in addition to hair scales, (5) possessing four types of body scales and (6) the presence of characteristic pit scales in the flagellar pit. Scale morphology was compared with previously described species, and the morphology of spiny (or stellate) body scales thought to be one of the most useful diagnostic characters in delineating species within the genus. The origin of pit scales is discussed and a similar origin for the third layer of flagellar scales of the type species,N. olivaceaStein is suggested.N. astigmaticashares many ultrastructural features with the type species, including the microtubular flagellar root system consisting of three different roots, one of which is multilayered. The validity of this root system as a generic character is suggested.
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