Shellos has two different forms: West Sea Shellos, which is pink and white in appearance, and East Sea Shellos, which is blue and green. They are found on the respective sides of Sinnoh's mountain range.
Shellos is a sea slug-like Pokémon whose appearance changes depending on which part of the sea it is found in. Both forms have amorphous, slug-like bodies, black oval-shaped eyes with yellow outlines, minuscule, dot-shaped noses, and wide yellow lips. Like real-world sea slugs, they have mantles covering the top halves of their bodies. These mantles are outlined in yellow, similar to their eyes. Unlike real sea slugs, however, they have bulbous heads and four small feet rather than one large foot.
The West Sea form's underside is white, and its mantle is pink, with several small spike-like protrusions on its back. On its head is a ring of pink, fleshy knobs resembling the gills of a nudibranch. West Sea Shellos' appearance is theorized to have been influenced by warm ocean waters.
The East Sea form, meanwhile, sports a green underside and a turquoise mantle. Two yellow-lined, flap-like protrusions, resembling cerata, are present along its back. On its head are two white-tipped tentacles resembling rhinophores that extend away from its face. East Sea Shellos's appearance is theorized to have been influenced by cold ocean waters.
Shellos lives along seashores; its color becomes more vibrant the better quality of the waters it lives in. It is also believed that Shellos's diet, which consists of plankton, also influences its form, though this has yet to be proven. The physical differences between both forms appear largely cosmetic; no significant changes in capabilities have been observed. While it can travel onto land, it can only stay on the shore for a limited time before its skin dries out. When Shellos' squishy body is pressed or squeezed, or when Shellos senses imminent danger, a mysterious purple fluid — theorized to be a kind of stress-induced greasy sweat — will ooze out of its body. This fluid is its defense mechanism against enemies; although harmless, it is very sticky and hard to wash off. Shellos has a friendly disposition and is said to have great regenerative capabilities. In the anime, West Sea Shellos can extend their necks to incredible lengths. It is unknown if the East Sea form can do this as well.
This species once had a shell on its back long ago and is considered a close relative to Pokémon such as Shellder. The Nurse Joy featured in Gateway to Ruin! revealed Mount Coronet's formation led to an allopatric speciation event, in which the original population of Shellos was separated into two. As a result, Shellos's color and other physical aspects began to vary due to environmental differences and population isolation over time. The two forms are still able to interbreed; the child normally takes the mother's form but takes the father's if bred with a Ditto. Recently, East Sea Shellos' population has been declining, while West Sea Shellos has become more abundant than before.
Shellos has two separate forms: West Sea Shellos and East Sea Shellos. The two forms differ in appearance only.
Shellos's most notable appearance is that of a companion of Mr. Fuego's. He typically keeps his East Sea Shellos on his shoulder, continuing to do so even after he accidentally imprisoned himself to avoid Team Galactic. It first appeared in Maddening Magby.
Shellos has two different forms: West Sea Shellos and East Sea Shellos. In most cases, where it is encountered in the wild determines its form. This is purely a cosmetic difference, and this Pokémon cannot change between forms.
West Sea Shellos is pink and white in color, whereas East Sea Shellos is blue and green in color. There is also a slight difference in shape depending on the form.
Shellos and its evolution were accidentally released in Pokémon GO on April 29, 2019, but were removed shortly after. On May 17, 2019, they made their official debut along with various other Pokémon from Generation IV.
Shellos is the only Pokémon with Sand Force that benefits from its sandstorm immunity, since every other Pokémon with the Ability are naturally immune to sandstorm damage due to their typing.
The Pokémon Scarlet and Violet Pokédex entries mentioning an increase in West Sea Shellos and a decrease in East Sea Shellos may be in reference to changes in the populations of real life sea slug species due to climate change — with species that better survive in warmer waters becoming more common.
Shellos is based on a sea slug. It resembles various species of nudibranchs, and its ability to secrete purple fluid may be based on sea hares, most of which secrete a purplish ink for self-defense.
Shellos may be a combination of shell and loss or lost (referring to its lack of a shell), or the German suffix -los (-less).
Karanakushi may be a combination of 殻 kara (shell), 無くした nakushita (to have lost), and 海牛 umiushi (sea slug; nudibranch).