interesting...I am doing an invert tank and would like to keep a variety of echinoderms, but I also would love to keep an arrow crab with them, I've seen videos of arrow crabs perched above sea cucumbers with no sign of predation (attached below). I have owned an arrow crab in the past and know they can eat snails and such, but knowing sea cucumbers are toxic maybe they know to leave them alone? I would like a second opinion.
Interestingly, I can't find anything on the interactions between arrow crabs and sea cucumbers - it seems they occupy entirely different niches in the wild, and I'm doubtful many people keep both in the same tank.
Interesting- yeah, it's likely using it as a replacement symbiont; I've heard of them doing that would corals before, but not cukes.So I decided to try it, here’s what happened:
Arrow crab (x1) and sea apple(s) were introduced at the same time, arrow crab showed no interest, later I found the arrow crab perched on top of the larger sea apple. now this isn’t exactly a problem, I can tell he is only picking debris off from the surface of the apple and he occasionally wanders away from it but every couple of minutes he ends up making the sea apple close, meaning it cannot feed.. which is a problem.
“the arrow crab (Genus Stenorhynchus) stays loosely in contact with the anemone—usually found on the sand around the anemone—and is considered a facultative symbiont”
maybe I tricked him into thinking they’re anemones? Or have I discovered a new symbiotic/commensal relationship??
Conclusion: they are indeed safe to keep with cucumbers but I wouldn’t recommend them with the filter feeding ones as they inhibit their ability to feed which can lead to starvation for the apple/cucumber.
