Asterolampra is primarily a fossil genus (Gombos 1980); the number of extant species is not clear, though there appear to be at least three. The valve surface is only partially areolate, with a series of hollow hyaline rays extending from a hyaline central area to the margin (Fig. 1, brightfield). These rays are open to the cell interior by means of elongate narrow slits, and open to the external environment by rimoportulae at the end of each ray. The rays are of equal shape and width, a characteristic which separates this genus from Asteromphalus. The rays are elevated above the valve surface so that the valves are radially undulated. The upper and lower valves of a cell are rotationally displaced, so that the rays are not superimposed when entire cells are seen in valve view.
According to Hasle & Syvertsen (1997), citing Hustedt’s earlier analysis, A. marylandica has a diameter of 50-150µm, with 13-17 areolae per 10µm, 4-12 rays. The size of the hyaline central area is 0.17-0.33 times the diameter (Fig. 2, phase contrast). It therefore has a wider (but mostly overlapping) morphological range than A. grevillei (Wallich) Greville, which has a diameter of 70-125µm, 20-22 areolae in 10µm, 7-17 rays, and a hyaline central area ~0.25 times cell diameter.
Asterolampra marylandica is primarily a tropical and subtropical oceanic species, sometimes found near the coast. Living cells have a many small discoid chloroplasts. It was seen only rarely in the IRL near the Fort Pierce inlet, and almost certainly is an adventitious occurrence.