An unseen species that spends long periods in hibernation, chosen by Picard as third-party arbiters under the Treaty of Armens precisely because they would be asleep for six more months.
The Grizzelas are a species known to the Federation and the Sheliak whose life includes a regular hibernation cycle lasting many months. They are neutral in the affairs of both powers, and nothing else is said about them.
They are mentioned in the Next Generation episode The Ensigns of Command. The Sheliak insist on the letter of the Treaty of Armens and refuse to give the Enterprise the three weeks needed to evacuate the human colony on Tau Cygni V. After a search through the enormous document, Picard invokes a clause that lets either side call for arbitration and names the Grizzelas.
Since they cannot wake for another six months, the treaty would be in abeyance all that time. Faced with the delay, the Sheliak give Picard the three weeks he had asked for.