Core discovery tiles are used in every game of Fathom.
They feature 4 species; Coral, Schooling Fish, Sea Cucumber and Crustacean.
Some core discovery tiles feature more than 1 species on the same tile; the number of times an icon appears in a set of 18 core tiles is shown below the images on the species guide.
Each expediton adds additional advanced species to the game which all have special scoring conditions.