The all-Vulcan crew of the USS Intrepid was killed by a giant single-celled organism, and Spock felt their deaths before the Enterprise destroyed the creature.
In 2268 Spock, on the bridge of the Enterprise, collapsed as he sensed the sudden deaths of the four hundred Vulcans on the USS Intrepid. The ship had been destroyed in the Gamma 7A system, where a huge single-celled organism drained energy and life from everything that came near, including an entire star system.
The Enterprise was drawn inside the amoeba, and Kirk faced choosing between Spock and McCoy to pilot a probe into it. Spock went, sent back crucial information and was rescued along with his shuttle. The Enterprise destroyed the organism with an antimatter charge just before it was due to reproduce.