Slug

From SporeWiki, the knowledge base dedicated to Spore

According to this video from E3, when your creature emerges from the primordial ooze, the creature emerges as a "slug", or a blank slate prompting the player to be creative in the creation of a unique creature entirely from the player's imagination.

It is unclear how the slugs will survive once they emerge. It may be that all other creatures of the time are also slugs or at least don't pose much of a threat. When your creature emerges from the sea you can see many of the same creatures. The creatures look like a brown sluggish type thing.

This seems to no longer be true, as a later video has shown that your creature as being an enlarged version of your final cellular species. If this is truly how creatures appear now, slugs may no longer exist in their initial form, and would instead have to be created that way by the user. A new trailer reveald that somtimes the slug (or worm) will emerge from the cell phase with random legs and starter feet.