A little Z. rex: on the predatory habits of the emperor shrimp

The Indo-West Pacific emperor shrimp, Zenopontonia rex (Kemp, 1922) from the family Palaemonidae, was hitherto known as a peaceful symbiotic crustacean, feeding on very small organisms or detritus and other organic particles trapped in its varied hosts’ mucus. However, at two occasions in Indonesia, Z. rex was observed capturing and subduing relatively large and agile animals, representing completely new observations for the species’ diet and feeding behaviour. In the first case, Z. rex associated with the large chromodorid nudibranch Ceratosoma tenue Abraham, 1876 captured another palaemonid shrimp ( Cuapetes sp.), only slightly smaller in size. In the second case, two individuals of Z. rex associated with a sea star, Echinaster luzonicus (Gray, 1840), were seen actively exploring the substrate under the star’s arms and one of them eventually captured and killed a juvenile/post-larval fish, probably a goby (Gobiidae). The second case represents one of the few in situ observations of a caridean shrimp killing a vertebrate.