The Lipul were one of the six sentient species that were known to reside on the artificial planet Gemworld, and were known to possess telepathic abilities. They resemble giant jellyfishes who live inside of the marrow of crystals. Their spirit travels the galaxy with a kind of astral projection, which are called "dreamships".
In 2172, the Lipuls used their dreamship abilities to send a Coalition crew of Humans and Vulcans on a 29 year mission to locate Gemworld and make first contact with the natives of that world. Of the crew, only Captain T'Mila was still alive as of 2376.
In early 2376, a Lipul was able to telepathically link with Lieutenant Melora Pazlar and Deanna Troi aboard the USS Enterprise-E and warn her that Gemworld was facing an ecological disaster which was destroying the planet. Captain T'Milia, also received this message and died shortly after; her physicians claimed that the telepathic messages she received were simply side effects of Bendii Syndrome
With this message, Pazlar and Troi were able to convince Captain Jean-Luc Picard to divert from Primus IV to Gemworld in time to prevent the planet's destruction. (TNG novels: Gemworld, Book One, Gemworld, Book Two; TTN novel: Taking Wing)