丁丁虫 砂壳纤毛虫
科学分类
域： 真核域 Eukarya 界： 囊泡藻界 chromalveolata 门： 纤毛门 Ciliophora

丁丁虫（Tintinnids）一译铃纤虫，或砂壳纤毛虫，是一种生活在水中的单细胞的原生动物，隶属于纤毛门（Ciliophora）旋毛纲（Spirotrichea）环毛亚纲（Choreotrichia）砂壳目（Tintinnida）(Lynn, 2008)。砂壳纤毛虫是水体微食物环中微型浮游动物（microzooplankton）的重要组成部分，主要摄食浮游硅藻、鞭毛虫和微微型浮游生物，在水体生态系统能量流动和物质循环中占重要地位。

砂壳纤毛虫的虫体生活在壳中，这个外壳大多呈壶形、花瓶形或管形，都有一个开口，有的在反口面还有一个较小的开口，虫体有一个柄固着在壳的后端，通过身体的伸缩可以将身体伸出和缩进壳内。在环境不利时，虫体会离开壳。砂壳纤毛虫的壳在动物界中是独一无二的， 下面介绍砂壳纤毛虫壳的壳的微细结构、粘附颗粒和生态学意义。

Tintinnids are ciliates of the choreotrich taxon Tintinnida, distinguished by vase-shaped shells called loricae, which are mostly protein but may incorporate minute pieces of minerals (Agatha, Laval-Peuto & Simon 2013). Fossils resembling tintinnid loricas in shape and size, Calpionellids, appear as early as the Ordovician period but are formed of calcite and as no extant ciliate taxa forms calcite shells they are unlikely to be tintinnids and probably not ciliates at all (Remane 1985). Fossils which can be reliably related to extant tintinnids (e.g. fossils of aggultinated lorica) are in the fossil record during the Jurassic but do not become abundant until the Cretaceous (Lipps, Stoeck & Dunthorn 2013). Tintinnids are an important part of the fossil record because of the rarity with which most other ciliates become preserved under the conditions of the marine environment. The loricae of some tintinnids are easily preserved, giving them a relatively good fossil record.