Zenopontonia rex is a robust shrimp growing to a length of about 3 cm (1.2 in), with females being rather larger and slightly less colourful.

The basic colour of this shrimp is orange-yellow to orange-red, with purple antennal plates, claws and walking legs.

Its range extends from the Red Sea, Réunion and Mayotte to Hawaii and French Polynesia, and from southern Japan to New Caledonia and northern Australia.

[3] Zenopontonia rex lives as a commensal on sea cucumbers such as Bohadschia, Opheodesoma, Stichopus, Synapta maculata or Thelenota, or on nudibranchs and other large molluscs including Asteronotus, Ceratosoma, Chromodoris, Cypraea, Dendrodoris, Hexabranchus, Hypselodoris and Pleurobranchus; occasionally it has been observed living in association with a starfish such as Echinaster or Gomophia.

This species is gonochoric; the male uses his first two pairs of walking legs to deposit sperm on the underside of the female's thorax, where the eggs are incubated until they hatch.