Climacodium biconcavum is a pennate diatom in the family Hemiaulaceae, found in warm, tropical to subtropical marine waters of the Atlantic, Pacific, and Indian Oceans. Diatoms are unicellular, photosynthetic microalgae that construct intricate silica cell walls called frustules, which serve as species identification characteristics. Climacodium biconcavum is recognized by its elongated, ribbon-like colonies of cells joined end-to-end, with distinctive biconcave cell profiles visible in side view. Like other marine diatoms, it is a primary producer, fixing carbon through photosynthesis and forming the base of marine food webs. Climacodium species are commonly found in warm, oligotrophic open-ocean waters and can form blooms when nutrient conditions are favorable. The species contributes to the biological carbon pump, with cells and colony chains sinking to deeper water after bloom collapse, transporting fixed carbon to the deep ocean. Marine diatoms collectively account for roughly 20% of global photosynthesis and play a critical role in the global oxygen cycle and carbon cycle. Climacodium biconcavum is studied in oceanographic surveys and sediment core analysis as an indicator of historical sea-surface temperatures and primary productivity conditions.