195 Helicotheca tamesis 泰晤士旋鞘藻 Phylum: Heterokontophyta 门：不等鞭毛門 Class: Mediophyceae 纲：中型硅藻綱 Order: Lithodesmiales 目：石絲藻目 Family: Lithodesmiaceae 科：石絲藻科 Morphology The frustules possess relatively flat and linear valve, with a rectangle girdle view. The length (pervalvar axis) is equal with width or slightly longer than width. Cells are either solitary or form twisted ribbon-shaped chains with varied length. Adjacent cells are tightly united through the valves with no apertures between sibling cells and obvious torsion frequently occurs between epitheca and hypotheca. Numerous small, and elongated granular chloroplasts are present in the cells. 形態 細胞殼面較平，整體呈線性, 殼環面觀為長方形。細胞長（貫殼軸）略高於寬（縱 軸）或二者等長。細胞單個生存或形成長短不一的扭曲的帶狀鏈。細胞通過殼面緊 密相連，相鄰細胞間無間隙。細胞上殼和下殼之間頻繁發生方向扭轉。色素體較多， 小且長，呈顆粒狀。 Ecology and distribution Helicotheca tamesis is a neritic predominantly warm water species. 生態與分佈 泰晤士旋鞘藻是近岸暖水性物種。 Size
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