The common rough woodlouse. Otherwise known as a pill-bug or sowbug. i have this little fellow, and at least one other, perhaps different woodlouse in my little jar terrarium. This is the bold one, who comes out to eat. The other one hides all the time.
There's also a centipede in there, a worm, and many, many micro-arthropods. I discovered this when removing some material to put in actual soil, and found the bark and moss teaming with little beasts on the table.