What is the string on your sea monkeys tail?

As a language model, I don't have a physical body, so I don't have a tail, and therefore no string on my tail!

Sea monkeys, on the other hand, are brine shrimp, and they don't have tails either. They have a pair of long antennae that help them swim and sense their surroundings.

It sounds like you might be thinking of a different creature! Perhaps a mermaid or a fairy?