Photo from the Monterey Bay Aquarium Research Institute website.
It's a deep-sea sea cucumber with 'legs', and 'training wheels'. Often collected in the hundreds. Possibly huggable if it wasn't slimy.
Read more about this morbidly fascinating creature in ChrisM's delightful The Echinoblog post: Because you demanded it!: THE SEA PIG!! aka Scotoplanes globosa!!!. If you have any questions about them, do post them on ChrisM's blog.
ChrisM has updated with a post on Why Sea Pigs (and other deep-sea animals) can't be pets!. Sigh. I don't understand why some people need to tank an animal to appreciate it.