During the Cambrian period, coral was only beginning to emerge. The simple corals and plant life dominated Cambrian seas. Though slightly easier than later Paleozoic oceans to assemble, a Cambrian coral reef diorama requires close attention to detail as well.
Here is a mini-tutorial and shopping list on how to build a fantastic set.
My Cambrian diorama:
[You must be registered and logged in to see this link.]What I use for corals:
(Out of this set, use the orange/yellow tube coral and green tube/branch coral!)
[You must be registered and logged in to see this link.]Safari Ltd. Vauxia and Charniodiscus:
[You must be registered and logged in to see this link.]Charniodiscus-resembling plant:
[You must be registered and logged in to see this link.]What I use for plants:
[You must be registered and logged in to see this link.]Besides these recommendations, any aquatic plant will do.
Furthermore, a trilobite fossil thrown in for decoration enhances the diorama.
[You must be registered and logged in to see this link.]Most Cambrian animals hung around the sea floor. Trilobites, worms such as ottoia, and other arthropods were less interested in swimming out in the open. Anomalocaris, jellyfish, and pikaia should be placed on stands (whether they came with the figure in the case of the Kinto Favorite pikaia and anomalocarids) or mounted in the plants.
As for wallpaper, which can add dimension to the diorama, Google images has several colorful and appealing Cambrian recreations.
Hope this was of use to someone.