Planktosphaeria gelatinosa is a marine phytoplankton characterized by its small, spherical to ovoid cells that may occur singly or in colonies. Each cell possesses a thin and delicate cell wall, sometimes surrounded by a mucilaginous sheath. Inside the cell, several chloroplasts facilitate photosynthesis, while the nucleus is centrally located. Colonies form with cells embedded in a gelatinous matrix. At certain life stages, Planktosphaeria gelatinosa may exhibit flagella for motility, aiding movement in marine environments. It thrives predominantly in coastal waters and open oceans, contributing to marine phytoplankton communities and playing a vital role in marine ecosystems’ nutrient dynamics.