| Zenopontonia rex | |
|---|---|
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| Z. rex with the nudibranch Glossodoris cincta | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| Infraorder: | Caridea |
| Family: | Palaemonidae |
| Genus: | Zenopontonia |
| Species: | Z. rex |
| Binomial name | |
| Zenopontonia rex | |
| Synonyms[1] | |
| |
Zenopontonia rex, theemperor shrimp orimperial shrimp, is a species ofshrimp in the familyPalaemonidae. It is found in shallow water in the tropical Indo-Pacific region. It lives in association with asea cucumber, anudibranch or other largemollusc, often changing its colour to match that of itshost.
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 antennae are modified into a series of plates that extend forwards from the head, and therostrum has a crest-like extension. The cephalothorax bears a small spine on either side. The first two pairs of legs bear pincers with short sensory hairs. The basic colour of this shrimp is orange-yellow to orange-red, with purple antennal plates, claws and walking legs. However, during the day, whitechromatophores in the skin expand and may cover much of the dorsal surface and tail fan; in other instances, the white colour appears as a median band, and the basic orange colour is revealed elsewhere. The colouring also varies depending on the shrimp's host; the classic colouring usually occurs when it is associated with a sea cucumber, but it sometimes matches the colour of its host, particularly when associated with anopisthobranch.[3]
Zenopontonia rex is native to the tropicalIndo-Pacific region. Its range extends from theRed Sea,Réunion andMayotte toHawaii andFrench Polynesia, and from southern Japan toNew Caledonia and northern Australia. It is found at depths down to about 40 m (130 ft), always living in association with a large sea cucumber, a nudibranch or other large mollusc,[3] perching on its back as its host moves around.[4] It livescommensally on a number of hosts, including thesea slugHexabranchus.[5]
Zenopontonia rex lives as acommensal on sea cucumbers such asBohadschia,Opheodesoma,Stichopus,Synapta maculata orThelenota, or onnudibranchs and other large molluscs includingAsteronotus,Ceratosoma,Chromodoris,Cypraea,Dendrodoris,Hexabranchus,Hypselodoris andPleurobranchus; occasionally it has been observed living in association with astarfish such asEchinaster orGomophia. There is often a pair of shrimps, or even three, on a single host, and then they usually have identical colouring. They keep to the dorsal surface or flanks, moving to the far side of the host if danger threatens. The shrimp feeds ondetritus on the seabed, as well as cleaning the surface of its host and feeding onmucus andfaeces. This species isgonochoric; 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. The larvae are planktonic.[3]
Recent studies have shown that the emperor shrimp display predatory habits. Such as in two occasions in Tulamben, Bali, Indonesia. In the first case, a single shrimp lived in associated withC. tenue when it attacked a small palaemonid shrimp. The second case involved two shrimps that lived symbiotically with the echinasterid sea star when it attacked a small post-larval fish. This showed that in occasions the Z. rex claws are strong enough to grip relatively large prey, they are actively searching for prey, and they are an opportunistic hunter.[6]
It' lives in water up to 45 metres (148 ft) in depth,[7] and can grow to a length of 1.9 centimetres (0.75 in).[8]
A. J. Bruce first described it in 1967 based on eight specimens ranging from 4 millimetres (0.16 in) to 7.6 millimetres (0.30 in).[9]
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Media related toPericlimenes imperator at Wikimedia Commons
