|First appearance||(4.02 "What Was Lost - Sacrifice")|
|Last appearance||(4.03 "What Was Lost - Resurrection")|
|Nickname(s)||Black Lagoon (John Crichton)|
|Portrayed by||Steve Le Marquand|
Oo-Nii was a mysterious creature who inhabited the planet of Arnessk.
As he could apparently live under water, the planet's magnetic summers did not force him to leave like others had to. During her stay on the planet, Noranti met Oo-Nii and was seen walking around with him on several occasions. The Interion archeologist Vella was also familiar with him but did not seem to care much for the creature. He saved Crichton from drowning and disappeared afterward. When the crew of Moya returned to Arnessk to fix Lo'La, they found out that it was Oo-Nii who killed Vella and that he was the one planning to sell the Darnaz probes. He forced Crichton to show him where the third probe was and nearly overpowered him in a fight, but Chiana arrived in time to save her friend and shoot down the creature.