This diatom can be found as single cells or in chains of up to six cells. It typically features a ring of fultoportulae along the valve face’s periphery, costae that may extend from the center to the edges of the valve, and a single labiate process. The central area of the valve face is often enclosed by an irregular siliceous ring and may or may not have central fultoportulae. Radial striations are often visible on the valve face, and hexagonal to polygonal areolae are commonly observed in the central region. The diameter of Thalassiosira pseudonana can range from 2.5 to 15 µm.