Diatomea

Diatomea, commonly referred to as diatoms, are a diverse group of photosynthetic microalgae within the division Bacillariophyta. They occur as unicellular organisms or in colonial forms and inhabit a wide range of aquatic environments, including oceans, freshwater, and moist soils, where light is available and silica is present. The hallmark of diatoms is their frustule, a silica-based cell wall composed of two interlocking halves that fit like a box and lid. Frustules display species-specific patterns of pores and ridges, and their intricate silica shells are well preserved in the fossil record as diatomaceous earth.

Most diatoms carry chlorophyll a along with the accessory pigment fucoxanthin, giving them a characteristic golden-brown hue. They are primarily autotrophic, contributing substantially to global primary production and to the silica cycle in the environment. Reproduction is mainly asexual; during division, the frustule halves separate and generate a new, typically smaller, daughter cell. After several asexual cycles, sexual reproduction occurs, producing an auxospore to restore full cell size and genetic diversity.

Diatomea exhibit substantial diversity, with estimates ranging from tens of thousands to hundreds of thousands of species. They are broadly categorized into centric and pennate diatoms, with varying shapes and motility; some pennate forms possess a raphe that enables gliding. Ecologically, diatoms form the base of many aquatic food webs and serve as important bioindicators of environmental conditions. They also have significant practical uses, most notably diatomaceous earth, which is employed in filtration, polishing, and as an abrasive material, in addition to applications in paleolimnology and industry.