Wicked Cool Host-Commensal-Parasite System

I really like symbionts.  I really, really like interactions among symbionts, and I especially like it when commensals/mutualists eat parasites.  

So, it is with great pleasure that I introduce to you this urchin-crab-snail system.  The common pencil sea urchin (Eucidaris galapagensis) is a host for parasitic snails (Sabinella shaskyi and Pelseneeria spp) and commensal crabs (Mithrax nodosus).  And the crabs eat the snails!

Sonnenholzner et al. (2011) did some neat field and lab work to figure out how fishing for urchin predators affects parasitism of urchins by snails in this cool system.  Hilariously, they sum up their findings in the first line of the discussion by saying that they “found that the enemy (fisher) of the enemies (fish and lobster) of the enemy (crab) of the urchin’s enemy (snail) was the urchin’s friend.”  Swag.

Here’s the quick (and simplified!) version of their results, but I highly recommend checking out the paper!

I drew this fishing pole myself.

Do you know of any other host-commensal-parasite systems?  Bonus points if you guess my FAVORITE system of all!

Reference:

Sonnenholzner, J.I., K.D. Lafferty, and L.B. Ladah. 2011. Food webs and fishing affect parasitism of the sea urchin Eucidaris galapagensis in the Galapagos. Ecology, 92(12): 2276-2284.