A new diatom species, Cocconeis cascadensis, is reported from streams in the Southern Cascade Mountain Range in California (USA). Light and scanning electron microscopy reveals morphological novelties related to the structure of the areolae on the sternum valve, which are surrounded externally by crater-like depressions, as well as apically elongated bumps in the submarginal hyaline area of the raphe valve. The valve morphology of the coarsely striated taxa, Cocconeis placentula var. lineata, C. pseudolineata and C. neodiminuta from the studied streams, and C. disculus from freshwaters in Europe, is presented for comparison. The newly described species possesses a unique combination of morphological features, representing an intermediary between the more complex valve ultrastructure of marine Cocconeis taxa and the freshwater members of the C. placentula species complex, with simple slit-like areolae. Cocconeis cascadensis inhabits cold-water mountain streams with low conductivity, low nutrients and low dissolved organic carbon concentrations.

中文翻译：

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Cocconeis cascadensis，一种来自美国北加州山区溪流的新硅藻

据报道，美国加利福尼亚州南部喀斯喀特山脉的溪流中发现了一种新的硅藻物种 Cocconeis cascadensis。光学和扫描电子显微镜揭示了与胸骨瓣上乳晕结构相关的形态新奇，这些乳晕在外部被火山口状凹陷以及中缝瓣边缘下透明区域中的顶端细长凸起包围。粗纹分类群 Cocconeis placentula var. 的瓣膜形态。来自所研究溪流的 lineata、C. pseudolineata 和 C. neodiminuta 以及来自欧洲淡水的 C. disculus 用于比较。新描述的物种具有独特的形态特征组合，代表了海洋 Cocconeis 分类群更复杂的瓣膜超微结构与 C. 胎盘种类复杂，具有简单的狭缝状乳晕。Cocconeis cascadensis 栖息在低电导率、低营养物质和低溶解有机碳浓度的冷水山溪中。