This page explains how to make a U.M.L. (Unidentified Marine Lifeform) appear in Endless Ocean Luminous.
To Make a UML Appear, Scan Creatures with Strange Biometric Signs
To make a UML appear, you have to find strange biometric signals. These are indicated by a flashing orange indicator in your scanner ring. When you have a flashing orange indicator, swim around until the indicator blinks rapidly. Then scan all the creatures around you. If the list has an orange dot above it, scroll through the scanned creature list to look at the one with an orange dot. This is the creature that is giving off strange biometric signs.
Starting a Mission
If there is no active mission, a mission will start after you scan a creature that is giving off strange biometric signs. During the mission, there will be orange circles on the map to show where other creatures giving off strange biometric signs can be found. If you haven't completed the map and can't see all of the circles, try mapping unmapped areas to find more orange circles. If you complete 80% of the map, it will automatically complete 100% of the map.
Complete the Mission to Make the UML Appear
When you scan all of the creatures giving off strange biometric signs, the UML will appear on the map in a large orange circle. Go to that circle and scan the UML to add it to your Creature Log. If you are in a Shared Dive and the creature has already been scanned, there will no longer be an orange circle indicating its location, but if you have established dive buddies, one of them may have tagged the UML on the map to help you find it. You can teleport to a dive buddy's location by selecting the buddy in the list and holding the A button.
How to Find UML Variants
There is a random chance that the rare variant of a UML will spawn instead of the normal UML. If you are hoping to find the rare variant of a given UML, it is recommended to use a dive site where you have found the normal version of the UML, then spawn it again the next time you find strange biometric signs, and keep spawning it until you get the rare variant.
The variant UMLs can appear in shared dives as well, and if a lot of people are participating in a shared dive, you can repeatedly spawn the UML more quickly than in a solo dive, giving you a better chance to get the variant UML in a shorter amount of time. However, since shared dives have a time limit, and since you can't control which UML appears, this is a less reliable method if you need a specific variant.