Lifeforms apparently composed of dark matter that Kathryn Janeway and three underperforming crew members met during a Delta Flyer survey in 2376, with one briefly entering the body of Crewman Telfer.
In the episode Good Shepherd, Janeway takes Mortimer Harren, Tal Celes and William Telfer on a routine away mission to help them find their feet. Something unseen strikes the Delta Flyer, tearing away hull plating and crippling the engines.
Harren suspects a dark-matter comet, but the crew then detect a presence aboard. It transports Telfer away and returns him with a creature inside his body. When it emerges, Janeway tries to communicate, but Harren, frightened, shoots and kills it against her orders.
More of the beings pursue the Flyer. Harren launches himself in an escape pod to draw them off, and Janeway retrieves him before igniting the radiogenic ring of a nearby gas giant to throw the shuttle clear. Whether the lifeforms were hostile or simply investigating is never settled.