28 groups based on valve symmetry and frustule structure: centric diatoms, which are radially symmetric and often circular, and pennate diatoms, which are typically bilaterally symmetric and elongated. 硅藻物種多樣性極高，據估計可能多達二十萬個物種，且每年都會有新物種發現。 不同硅藻的主要鑒定主要依據硅質細胞壁整體外觀以及超顯微結構。大多數硅藻 細胞粒徑一般位於2 微米到200 微米之間，少數物種會大於200 微米。硅藻的硅 質壁分為兩半，其中一半（上殼）比另一半（下殼）稍大。硅質壁的頂端和底端稱 為殼面。硅藻細胞在顯微鏡下呈現兩個不同的面觀：殼面觀和殼環面觀。殼面觀是 從硅質壁頂端或底端殼面觀察，而殼環面觀則是從側面觀察。基於殼面對稱性和硅 質壁結構，硅藻一般被分成兩大類，中心硅藻和羽紋硅藻。中心硅藻一般輻射對稱， 大多數傾向於圓形，而羽紋硅藻兩側對稱，較為瘦長。 Diatoms are a prominent component of marine phytoplankton, exhibiting high abundance and widespread distribution. They inhabit the euphotic zones of various marine environments, including estuaries, coastlines, and open oceans, spanning from spanning polar to tropical regions. Additionally, certain diatom species can be found on sediment and surfaces of intertidal reefs, seagrasses, and macroalgae. Serving as the foundation of the marine food chain, diatoms contribute significantly to marine primary productivity, accounting for 40% of it, and play a crucial role in global biogeochemical cycles. Some diatoms have the capacity to form blooms in estuarine and coastal waters. Notably, in the coastal waters of Hong Kong, diatoms have caused 144 blooms between 1975 and 2023. It is important to note that certain diatom species are toxic; for instance, certain Pseudonitzschia species can produce domoic acid, leading to amnesic shellfish poisoning and posing significant threats to the aquaculture industry, ecosystem stability, and human health. 硅藻是極為重要的海洋浮游植物，豐度高，分佈廣。從極地到熱帶，從河口、近岸 到大洋的幾乎所有環境的真光層，都有硅藻發現。硅藻也能在沉積物、潮間帶礁石、
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