Nothing like Admiral Ackbar, I'm afraid. They are amorphous beings with a smokey, mistlike consistency. They appear as an inverted teardrop, with a 3-foot-long prehensile tail.
Villains' Lorebook, page 70.
I think they're supposed to be related to the nishruu (3rd Ed. Monsters of Faerun) and the hakeshar (the Avatar trilogy of adventures: Shadowdale, Tantras, Waterdeep).
I am planning to reconstruct the scene from the Azure Bonds novel where Alias fights one of these kalmari in the inn in The Shadow Gap.