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Scientific classification
Domain: Eukaryota
(unranked): Alveolata
Phylum: Ciliophora
Class: Spirotrichea
Subclass: Choreotrichia
Order: Tintinnida
Kofoid & Campbell, 1929

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. Although appearing as early as the Ordovician period, tintinnids became abundant in the fossil record during the Jurassic. 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.

Like other protists, tintinnids are complex-celled (Eukaryota) organisms. Tintinnids are heterotrophic aquatic organisms. They feed primarily on photosynthetic algae and bacteria. They are part of the microzooplankton (between 20 and 200 micrometres in size). Tintinnids are found in marine and freshwaters. However, they are most common in salt water and are usually present in concentrations of about 100 a liter but can reach abundances of several thousand per litre. Characteristics of their lorica, or shells, are used to distinguish between the roughly 500 species described.

Many species appear to have wide distributions (for example from the Chesapeake Bay to New Caledonia) while others are restricted to certain areas, such as arctic waters or coastal seas. Nonetheless, in any given locale dozens of species can be found. Like other members of the microzooplankton (such as oligotrich ciliates, heterotrophic dinoflagellates, radiolarians, etc.), tintinnids are a vital link in aquatic food chains as they are the 'herbivores' of the plankton. They feed on phytoplankton (algae and cyanobacteria) and in turn act as food for larger organisms such as copepods (small crustaceans) and larval fish.

The image is a specimen of Dictyocysta mitra from the Bay of Villefranche in the Mediterranean Sea. The hair-like projections pointing out of the top of the shell are the cilia of the cell. The cilia generate a water flow across the mouth of the cell, bringing food into contact and move the tintinnid. Their swimming pattern is rather 'jumpy'- or dancing- they are part of the 'choreotrichs' which means dancing hairs from their swimming behaviour and cilia.