Well so I have a crab in my marine tank... and one I didn't add in! Contaminants are always likely in saltwater tanks so in a way, I figured it might someday happen. I'm pretty sure this guy is a Marsh Crab (Sesarma reticulatum) which is supposedly mostly herbivores. But I don't trust crabs! On average they are not picky with who or what they taste!
This specimen is relatively small. P. diogenes is the world’s second-largest hermit crab species, growing large enough to inhabit a full sized queen conch shell and beaten only by the terrestrial coconut crab, which is a hermit crab that stops using shells when it matures.
I can only assume that the the “diogenes” in its name comes from some parallel drawn between the hermit crab’s shell and the philosopher’s habit of sleeping in a large jar.