stolen costume design - infringing on personal invention

I created a costume designed to fit many sizes in one piece. The outside of it looks similar to a movie costume, but is neither the same material, or exact replica by any means. I posted this on a merchant web site for sale, less than a week later another person posted my same design and began selling it. Because of the complexities of the design, and the same materials used, I feel they are infringing on my personal invention. Is it a patent, trademark, or copyright infringement? The description was almost identical as well. Since this was a published item and sold to public prior to this other person even listing, am I protected automatically? What can I do about this?

[msgny]

It is patentable and copyrighted--they definitely can be sued--even using your common law rights regardless of whether you filed anything or not.

In the event that copyright protection is not available, there are alternative areas of law that may provide shelter for clothing designers. These areas include: patent, trademark, unfair competition, and misappropriations/conversion. A design patent serves to protect that which gives a distinctive appearance to articles of manufacture, whether from their configuration or ornamentation. A trademark protects against the unauthorized use of one's mark to identify the goods of another. In recent years, another aspect of trademark law, trade dress, the overall appearance of a product, has been expanded to include a product's design as another avenue for protection. An unfair competition claim may be made where the defendant copied the plaintiff's design and that copy is "passed off" as the plaintiff's product. Lastly, misappropriations protect against the appropriation and exploitation of another's labor, investment, and skill and conversion protects against the wrongful possession of a tangible embodiment of a work. Although copyright is the most frequent guard against design piracy, alternative areas of law should be explored to determine what other protections are available.