硅藻（Bacillariophyceae）是真核藻类的一个主要类群，同时也是最常见的一种浮游植物。多数为单细胞生物，尽管有些种类可以丝状或带状群体（如Fragilaria）、扇状群体（如Meridion）、锯齿状群体（如Tabellaria）以及星形群体（如Asterionella）形式存在。硅藻在食物链中属于生产者。硅藻的一个主要特点是硅藻细胞外覆硅质（主要是二氧化硅）的细胞壁。硅质细胞壁纹理和形态各异，但多呈对称排列。这种排列方式可作为分类命名的依据。但是这种对称并不是完全的对称，因为硅藻细胞壁的一侧比另一侧略大一点，这样才能嵌合在一起。化石遗迹显示，硅藻最迟起源于早侏罗纪时期。仅中心硅藻类的雄配子具鞭毛，可以游动。硅藻一直以来是一种重要的环境监测指示物种，常被用于水质研究。分类上归为一纲，辖下有中心硅藻目及羽纹硅藻目。此外也是近海的优势类群。

Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons (e.g. Fragilaria), fans (e.g. Meridion), zigzags (e.g. Tabellaria), or stars (e.g. Asterionella). The first diatom formally described in scientific literature, the colonial Bacillaria paradoxa, was found in 1783 by Danish naturalist Otto Friedrich Müller. Diatoms are producers within the food chain. A unique feature of diatom cells is that they are enclosed within a cell wall made of silica (hydrated silicon dioxide) called a frustule. These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical, hence the group name. The symmetry is not perfect since one of the valves is slightly larger than the other, allowing one valve to fit inside the edge of the other. Fossil evidence suggests that they originated during, or before, the early Jurassic period. Only male gametes of centric diatoms are capable of movement by means of flagella. Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality.