''Cymo melanodactylus'', the furry coral crab, is a species of small decapod

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

in the family

Xanthidae Xanthidae is a family of crabs known as gorilla crabs, mud crabs, pebble crabs or rubble crabs. Xanthid crabs are often brightly coloured and are highly poisonous, containing toxins which are not destroyed by cooking and for which no antidote is ...

. It is found in the Indo-Pacific Ocean and lives in crevices and on the surface of corals in the genus ''

Acropora ''Acropora'' is a genus of small polyp stony coral in the phylum Cnidaria. Some of its species are known as table coral, elkhorn coral, and staghorn coral. Over 149 species are described. ''Acropora'' species are some of the major reef corals r ...

''.

Description

The

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

and limbs of ''Cymo melanodactylus'' have the appearance of being covered with short fur. It has large pale blue, stalked eyes, a spiny carapace with a shallow groove down the middle and grows to about wide. It typically has black fingers to its claws but is difficult to distinguish from the rather similar '' Cymo andreossyi'' on claw colour alone as some individuals have white finger tips and others have white fingers with black bases. A more reliable feature to distinguish between the two is the orange granulations on the carapace of ''Cymo melanodactylus''.

Distribution

''Cymo melanodactylus'' is found in the Indo-Pacific Ocean. Its range extends from the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...

and

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

French Polynesia )Territorial motto: ( en, "Great Tahiti of the Golden Haze") , anthem = , song_type = Regional anthem , song = " Ia Ora 'O Tahiti Nui" , image_map = French Polynesia on the globe (French Polynesia centered).svg , map_alt = Location of Frenc ...

and

Wallis and Futuna Wallis and Futuna, officially the Territory of the Wallis and Futuna Islands (; french: Wallis-et-Futuna or ', Fakauvea and Fakafutuna: '), is a French island collectivity in the South Pacific, situated between Tuvalu to the northwest, Fiji ...

Biology

''Cymo melanodactylus'' is an obligate

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

of ''

'' spp. corals. On the large table coral ''

Acropora cytherea ''Acropora cytherea'' is a stony coral which forms horizontal table like structures. It occurs in the Indo-Pacific Ocean in areas with little wave action, favouring back reef environments from depth. Description ''Acropora cytherea'' is a colo ...

'', there are usually just one or two of these crabs per head of coral. The crabs feed mostly on

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

secreted by the coral, but also consume

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and suspended particles and nibble the living tissue, though the coral seems little harmed by this. In 2010 in the

Chagos Archipelago The Chagos Archipelago () or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives archi ...

, infestations of as many as 47 of these crabs were found on individual heads of coral and these corals exhibited dead and dying tissue. The crabs were in close proximity to the damaged tissues but it was unclear whether the crabs were the original cause of the damage or whether they had moved in to exploit the already dying tissues. A more recent study has shown that ''Cymo melanodactylus'' is attracted to acroporid corals suffering from

white band disease White band disease is a coral disease that affects acroporid corals and is distinguishable by the white band of exposed coral skeleton that it forms. The disease completely destroys the coral tissue of Caribbean acroporid corals, specifically ...

and that the disease advances at a much slower rate when the crabs are present than it does when they are absent. In the

Seychelles Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, V ...

, this crab was found living on a different species of coral, ''

Acropora formosa ''Acropora muricata'', commonly called staghorn coral, is a species of acroporid coral found in the Gulf of Aden, the Red Sea, Indian Ocean, Persian Gulf, Australia, central Indo-Pacific, Japan, Southeast Asia, the East China Sea and the ocean ...

''. A single coral head supported a mated pair, a single female and some juveniles.

References

{{Taxonbar, from=Q5199744 Xanthoidea Crustaceans described in 1852