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.