Spines are 14 in 10 micrometers (Stoermer and Yang 1969).
As a frame of refrence here is some information on a different Thalassiosira species which is not found in the Great Lakes.
Here are two pictures, one was taken using differential interference contrast
Thalassiosira baltica (Grunow in Cleve et Grunow 1880) Ostenfeld 1901, p. 290
(VanLandingham VII 1978).
This species has a rectangular gurdle view, a slightly slanted mantle and a flat valve face. The face is smaller near the margin and has radial rows of areolae. The mantle has areolae as well but they are smaller than those on the valve face. The mantle has a serrated rim. This species is often found in fairly long chains.
It has been found that salinity is important to this species so it is found only in bracish water. (Hasle 1978).
Diameter is 20 to 120 micrometers (Hasle 1978).
Areolar are 10 to 24 in 10 micrometers (Hasle 1978).