Cyl was a Trill symbiont whose hosts included Neema and Taulin.

In 2280 Neema Cyl learned from her mother, Audrid Dax, of the discovery of the Parasites and the threat they posed to Trill. All successive hosts of the Cyl symbiont dedicated themselves to research on these creatures. A later host Taulin was a Watcher of the parasites. (DS9 - The Lives of Dax short story: "Sins of the Mother", DS9 novel: Unity)