I knew the photo above would be difficult to identify, but I was happy that everyone at least figured out it was a spider. As a side note, I hope everyone realizes you can click on the photo to see a larger version.
One commenter, biozcw, ventured that it might be an Argyrodes species. That’s close, because the species I believe I have here, Ariamnes attenuatus, was formerly placed in that genus.
This spider was hiding beneath a large leaf. At only 15mm as shown in the initial photograph, it’s small and virtually disappears when assuming that cryptic position. Here’s a decidedly more spider-like pose. You can just barely see a strand of silk stretching from the spinnerets towards the upper right corner of the image.
The abdomen is somewhat bendable, as shown here. One has to wonder if that lighter colored abdominal tip isn’t perhaps wiggled to attract prey.
Sara Rall ventured that it might be an ogre-faced spider (Deinopis sp.)? That’s a good guess, given the elongate body. What’s interesting is that this species might share the same prey capture strategy. As noted here, some Ariamnes species catch other spiders with a net.
I arrived at the identification by first determining it was an Ariamnes species and then checking the World Spider Catalog. There, I saw that A. attenuatus is the only species in Costa Rica.
Here’s a few more images.
Finally, here’s a video of a different Ariamnes species.
Watching the spider, I’m even more inclined to imagine the tip of the abdomen being used as bait. You can see how the abdomen is long enough to actually bend over and dangle in front of the spider. Given that it may prey on other spiders, perhaps it’s used to teasingly pluck the thread’s of another spider’s web! Towards the end, the spider assumes a linear pose.
Too bad they don’t occur where I live. I’d love to keep one for awhile to see how it behaves.