Dendronephthya Crab, Hoplophrys oatesi
Photo by Rickard Zerpe

In this edition of Inverts We Wish We Could Have, which showcases unique invertebrates that are rarely or never seen in the aquarium trade, we spotlight the Dendronephthya Crab, Hoplophrys oatesi. The genus Hoplophrys is monotypic, containing the single species H. oatesi. These minute, true crabs are found throughout the Indo-Pacific region and grow to approximately 2.0 cm. They are often found in pairs, at depths between one and ninety meters and live symbiotically with Dendronephthya corals.

Dendronephthya Crab with eggs
Photo by Rickard Zerpe

Dendronephthya Crabs have a spiky carapace with bright pink, yellow, white, and orange coloration which matches the coral they live on. To further enhance their camouflage, Dendronephthya Crabs will also cut polyps off of the host coral and attach them to their bodies. This behavior is similar to that of decorator crabs and helps make this species an expert at blending into its surroundings. The crabs have a mutualistic relationship with the host coral: They help keep the coral clean of debris and defend the coral from predators, while the coral provides these crabs with shelter and food, as the crab eats the coral’s leftover food.

Dendronephthya Crab, Hoplophrys oatesi
Photo By Rickard Zerpe

While Dendronephthya Crabs would appear to be interesting aquarium inhabitants and occasionally enter the aquarium hobby as hitchhikers on Dendronephthya corals, they are really not suitable for aquariums. Dendronephythya corals are non-photosynthetic and are notoriously one of the most difficult soft corals to keep in aquariums due to their highly-specialized feeding requirements, such as small live foods and frequent feedings. Even in a dedicated biotope aquarium for non-photosynthetic corals, Dendronephythya corals are extremely difficult to keep alive. Without their natural host coral, Dendronephthya Crabs are unable to survive in the hobbyist aquarium environment. Coveted by recreational divers and underwater photographers for their unique appearance, this species is one that is best enjoyed in its natural habitat.

Reference:

Kuo, P H, Lin C W (2013) First record of the soft coral associated crab Hoplophrys oatesi Henderson, 1893 (Crustacea: Decapoda: Epialtidae) in Taiwanese waters. Platax 10: 95-100.

Dendronephthya Crab with coral polyps on its rostrum
Photo by Rickard Zerpe