Gomphonema gremainii resembles Gomphonema validium var. elongata which has a more truncated head pole. The ultrastructure is consistent with other Gomphonema species having puncta with external flaps C-shaped, The apical pore field porelli are structurally different and separated from the striae puncta. Septa and pseudosepta are present at the poles. (Kociolek and Stoermer 1990).
This taxon grows in deep water, (8-15 meters) attached to rocks in nearshore habitats in Lakes Superior, Michigan and Huron. (Kociolek and Stoermer 1990).
The valve is linear-clavate to lanceolate with an apiculate head pole. The foot pole is narrow. In the central area the median stria is longer that the other striae and comes close to the isolated stigma. The axial area is of variable width. The raphe is lateral undulate. (Kociolek and Stoermer 1990).