27 Chapter 2. Diatoms 第二章 硅藻 Diatoms are unicellular organisms characterized by a siliceous cell wall and yellowbrown chloroplasts. They occur either as solitary cells or in colonies, forming various shapes such as chains, ribbons, fans, zigzags, or stars. Most diatoms are photoautotrophic, with only a limited number exhibiting heterotrophic behavior. The observation of diatoms dates back to 1703, with the establishment of the first diatom genus in 1788. The classification of diatoms has undergone continuous evolution over the past two centuries, leading to ongoing debates and controversies at the present day. 硅藻是一類具有硅質細胞壁的單細胞生物，色素體黃褐色。硅藻一般獨立生活或形 成鏈狀、帶狀、扇形、之字形或星狀的群體。 絕大多數硅藻是光合自養，只有極 少數物種為異養。硅藻於1703年第一次被觀察到，並於1788年第一個屬被建立， 距今已二百到三百年。兩百多年來來硅藻的分類體系一直不斷變化，直到現在仍存 在許多爭議。 Diatoms exhibit a remarkably high level of species diversity, with estimates up to possibly 200,000 species, and new species being described regularly. Species differentiation in diatoms primarily relies on the overall shape and ultrastructure of their siliceous cell walls, known as frustules. The size of diatom cells typically falls within the range of 2 to 200 μm, with only a limited number exceeding 200 μm. The frustule is composed of two halves, with the epitheca slightly larger than the hypotheca. The ends of the frustules are referred to as valves, and diatom cells can be observed in two distinct views under a microscope: the valve view, which shows the top or bottom valve of the frustule, and the girdle view, which provides a side view. Diatoms are generally categorized into two
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