Eggs

Eggs are the unhatched forms of certain types of Fauna. Until they hatch the game will not identify them. However, an egg can be identified by where it was found, its appearance, and its size (See table below).

After an egg is analyzed, you can put it inside a Large Aquarium. The egg will take about 2-3 in-game days to hatch, with the exception of the Reefback. When hatched, the creature within the egg will be a smaller version of its respective species.

Eggs can be found in their species' respective Biomes.

More information and animations can be found on Trello.

Cycle
After placing an egg inside an Aquarium, it will stay where it was placed. After about one in-game day, the egg will begin to move and pulse. After three to five in-game days, the egg will hatch into a smaller version of its species. This egg will slowly grow until it is mildly full sized or can fit in the Large Aquarium. Baby creatures can be picked up and placed outside in the water, where they will instantly become fully grown. An aggressive creature will not attack the player if it is hatched in the aquarium, allowing the player to scan it. However, if it is released outside it will revert to its aggressive behavior.

Eggs
It is worth noting that many Eggs are affected by the in-game physics engine, and as such will roll into strange places. An example of this is finding a Stalker or Sand Shark egg in the Jelly Shroom Caves.