OSX File Extension

[JB]

Years ago you could create a file type or extension like jpeg, zip, pict etc.
and then you would need to register that extension with Apple.

If I create a new file extension do I need to register that extension with
Apple or just start using it.

The reason I am asking is I am creating a new form of compression for
files and similar to zip files I want my own extension after the file name.
The compression is not zip or any other and no other program will be
able to expand it.

JB