Ryan Photographic - Xanthidae - Poison or round crabs
The family Xanthidae is a large crab family with 433 species in 80 genera. They are typically toxic, containing substances which don't break down with cooking. The toxins appear to be produced by symbiotic bacteria. They are often brightly colored, which perhaps warns potential predators of their toxicity. They have a variety of common names including: egg crab, rock crabs and spooner crabs. A nice discussion of the xanthid species in Singapore can be found here.
Etisus dentatus Many-toothed spooner crab
Etisus dentatus Many-toothed spooner crab with inflated Diodon liturosus Kri Eco, Raja Ampat IMG_8255. The spooner crab dropped onto the porcupine fish as I was taking the photo. In response the fish inflated (almost instantly).
Gaillardiellus species (maybe) Raja Ampat IMG_1308
Leptodius sanguineus Rock pool crab
Possibly Leptodius sanguineus Rock pool crab, Namena, Fiji img 140
Lybia tesselata Mosaic boxer crab
Lybia tesselata Mosaic boxer crab, Magic Bay, Rao, Morotai, Indonesia 5P7A7513. This crab holds a sea anemone in each chela. As well as using them for defense it cleans food off the anemone tentacles.