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Uca signata (Family Ocypodidae)

Distinctive Fiddler Crab

Distribution:

Distinctive Fiddler Crab has a northern tropical Australian distribution. It ranges from Derby, northern WA, across northern shores, including NT, to Maryborough and Gladstone, Qld (WA, NT, QLD).

Features:

The carapace of the male Distinctive Fiddler Crab is a dull blue-green in colour with white marbled markings. It grows to 20-25mm across the carapace. The major chelae of the male are grey to white, with red-brown and grey-blue parts to the arms. The eyestalks are orange-brown while the legs are brown to blue grey. The mouthparts are brownish-blue with a white band. The carapace of the female is brown with extensive marbling on the front section. The eyestalks are orange-brown.

The carapace of the male crab appears to be and feels smooth, while the carapace of the female both looks and feels to be finely granular. The front of the carapace is narrow, while the frontal groove is broad and shallow. The eyebrows are very narrow, long and extend to beyond three-quarters of the eye channel, called the orbit. The eyestalks are reasonably thick.

On the largest chelae of the male fiddler crab, the upper moveable finger is longer than the fixed lower finger. The median groove on the lower finger is very long, but is indistinct. There may be felt pile within the chelae gape.

A more full description is found in George & Jones (1982).

Ecology/Way of Life:

The Distinctive Fiddler Crab is found on sandy mud on the upper levels of gentle sloping creek banks. It may be found on river banks below the Flamed Fiddler Crab, Uca flammula, and the Compressed Fiddler Crab, Uca coarctate, and above the Polished Crab, Uca polita.

Interaction with Humans/Threats:

The Distinctive Fiddler Crab has an extensive distribution range across remote northern Australia, occurring in many locations far from human habitation. It is therefore probably under no threat from human interaction.

Other Comments:

Uca signata, Hess, 1865. The type locality for this crab is recorded by Hess as Sydney, NSW, which is most doubtful. Hess named the type specimen Gelasimus signatus. Other synonyms are Uca signata, Crane 1975, Uca bellator, Macnae 1966, Uca (Australuca) bellator signata, Crane 1975 and Uca (Australuca) bellator minima, Crane 1975.

Signata comes from the Latin word signatum or signum, meaning a sign, or full of meaning and being significant.

Further Reading:

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. New Holland Press, Sydney.

George, R. W. & Jones, D. S. (1982). A Revision of the Fiddler Crabs of Australia (Ocyponinae: Uca). Records of the Western Australian Museum, Suppl. No. 14. P.53-56.

Jones, D. & Morgan, G. (1994). A Field Guide to Crustaceans of Australian waters. Reed.

Acknowledgments:

Text, map & photograph by Keith Davey.

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