I am guessing you have been visited by a slime mold. It moves like an amoeba, and engulfs organic material for food. Kewl beans to you - I LOVE slime molds, because they are so ....well........alien and slimy . Looks like it ate the leaf of the shrub - (a laurel) - judging from the green thing sticking up. Google for slime molds - amazing creatures, those.

By jove, Wannadanc, you're right!

http://waynesword.palomar.edu/slime1.htm

At the risk of sounding overly girlie ... YUCK!

Apparently, if i leave it alone, it will eventually go away. Alternatively, i can just turn over the mulch there to cover it. I think i'll do the latter. It may be an "amazing creature," but i don't want it staring at me while i garden ... :)

Do they eat slugs? If they do .... I want some!

Looks like you've been 'slimed'.
It's relatively common in bark mulch and not a problem.