Pretend that you are a Zoologist and you are studying the Sea-Monkey. You have already determined from the characteristics of life that Sea-Monkeys are a life form. Secondly, you determined that they were made of many cells combined and were thus Eukaryota Domain. Now, you have to look at the Sea-monkey to determine if they are plant, fungi, protists, or animal. You noticed that Sea-Monkeys swim in saltwater. Plants and fungi do not move[1], but Protista and animals do. So, Sea-Monkeys are Protista or animals. Animals are multicellular, while protozoa are microscopic single-celled organisms.[2] Sea-Monkeys are not microscopic and they are multicellular. Sea-Monkeys are animals!
Wiki, Kingdom (biology), https://en.wikipedia.org/wiki/Kingdom_(biology)
A Level Biology, The Five Kingdoms Classification System, https://alevelbiology.co.uk/notes/the-five-kingdoms-classification-system/
[1] Study.com, The Evolution of Plants and Fungi: Characteristics & Evolutionary History, https://study.com/academy/lesson/the-evolution-of-plants-and-fungi-characteristics-evolutionary-history.html
[2] WikiDiff, Animal vs Protist - What's the difference?, https://wikidiff.com/animal/protist