Here is a lovely illustration of an ammonoid, crinoid, rugose corral, archimedes and brain corral. This is my quick depiction of a cretaceous marine environment (the ammonoid’s sutures are characteristic of the cretaceous). But wait! Archimedes and rugose died out by the Permian, this sketch is as misleading as Jurassic Park! Well at least it’s invertebrates (sorry to all my vertebrate peeps).
Personal fun fact: one day a hope to find a crinoid calyx!