TRANSFER OF THE MARINE DIATOM DIMEROGRAMMA HYALINUM HUSTEDT TO THE NEW ARAPHID GENUS HYALONEIS

Abstract

Dimerogramma (Dimeregramma) hyalinum Hustedt, a relatively common diatom of marine littoral benthic assemblages, was described from mud samples collected from Beaufort, North Carolina, U.S.A. in 1955. Hustedt and later workers noted that the frustule of this species was completely hyaline. Studies of D. hyalinum from the type sample and from material collected from Scripps Beach, California, U.S.A. in 1972 and Beaufort, North Carolina in 2006 with the light and scanning electron microscopes confirmed the hyaline nature of the valve face and cingulum, but revealed the presence of apical slit fields located on the mantle at both apices of the valve. The valves of D. hyalinum lack the uniseriate striae composed of round areolae, sternum, transapical ribs, and spines arising near the mantle of the valve characteristic of Dimeregramma Ralfs in Pritchard. Furthermore, the apical pore fields composed of loosely packed porelli found in Dimeregramma differ markedly from the apical slit fields observed in D. hyalinum. Results of these studies suggest that D. hyalinum is sufficiently unique from Dimeregramma and araphid genera with apical slit fields to warrant its transfer to a new araphid genus, Hyaloneis, in the Fragilariaceae.