Looks pretty much like alien creatures, but these colorful "snails" are actually wonderful things on the bottom of the sea.
Nudibranchs are a type of molluscs, with the same family as the slugs but no shells.
In Latin and Greek, sea cucumbers mean 'carrying the ceiling'.
Sea cucumber has lost its shell after its larval stage.
These photos were taken in the waters of Indonesia, the Philippines and Papua New Guinew, the Mediterranean and the Red Sea.
Photographer Franco Banfi traveled around the world to capture these pictures.
There are about 3,000 species of sea cucumbers in the world.
We can catch them crawling on rocks, on seaweed, sponges, corals .
In most species, the gills are on the back of the sea slug.
See also: Sea slug blooming under the ocean (2).
They live at all sea level, but reach the largest size and have the most biodiversity in warm, shallow waters.
Scientists believe that this species has evolved in a colorful way to disguise its surroundings, avoiding enemies.
Another theory is that this may be a way to warn predators that they can be poisoned by touching these colorful creatures.
