From Creatures Wikia
Spriglysium Nebula (known fondly by Miff simply as "Tree") was an add-on for Creatures 2 that added new areas to Albia including an underwater cavern (which was suitable for water-breathing Norns and air-breathing Norns at the flick of a switch!), a large extension to the tree house, and a room above the pyramids. It was created by Ali for Albia 2000, where it can be downloaded. It doesn't clash with the Ocean Expansion Pack per se, but the rooms overlap.