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Uca vomeris (Family Ocypodidae)

Orange-clawed Fiddler Crab

Distribution

Distribution:

The Orange-clawed Fiddler Crab has a south-western Pacific Ocean distribution, including northern and north-eastern Australia. It ranges from Darwin, NT, east and south through Qld to Sydney, NSW (NT, QLD, NSW).

Features:

The male fiddler crab has a conspicuous brilliant orange coloured dominant claw that is called chelae. While the male has one chelae much larger than the other, the female crab has equal-sized chelae. Specimens from northern Australia are more brightly coloured than southern examples.

The carapace of the male both feels and looks to be smooth, while the female carapace both appears and feels very finely granular. The front is narrow, while the frontal groove is a wide triangle. Its eyebrows are very narrow, long and extend from two-thirds to three-quarters of the eye-channel or orbit. The eyestalks are thin.

The moveable finger of the chelae is longer than the immoveable finger. There is no long medial groove on the lower finger, but there is a groove on the upper finger. There is a trace of felt pile in the gape between the fingers. For a more detailed description see George & Jones (1982).

The carapace is brown-black in colour with dull blue-green blotches. The female has more blotches. The Major chelae of the male is coloured orange, merging into grey with an orange tinge, to pink and white. The smaller chelae may be grey-orange while the female chelae are blue-green merging to orange-pink. In both sexes the eyestalks are brown-grey, while the legs are dull orange-brown. The mouthparts are blue-grey tinged with turquoise.

For a full description of this species see George & Jones (1982).

Ecology/Way of Life:

The Orange-clawed Fiddler Crab occurs on unshaded sandy mud at the lower tide levels of open bays and creeks. It is often found on isolated sand and mud banks. The orange chelae of the males look like brightly coloured decaying leaves, waving on the mudflat. The ritualistic waving of the chelae is to repel other males, and attract females. It is usually found beneath the levels occupied by Uca polita, Uca longidigita and Uca seismella.

Preferred Image

Interaction with Humans/Threats:

The Orange-clawed Fiddler Crab is a common fiddler crab in north-eastern Australian estuaries. Chemical spills near our ports could pose a threat to this species.

Crane (1975) was unable to give separate descriptions for the suggested six subspecies of the species Uca vocans (another name for Uca vomeris). She suggested that there was interbreeding and hybridisation between the forms.

Other Comments:

Uca vomeris, McNeill, 1920. McNeill found the lectotype specimen at South West Rocks, NSW, in 1920. He named it Uca marionis var. vomeris. Other synonyms are Uca marionis, Ward 1928, Uca vocans, Macnae, 1966 and Uca (Thalassuca) vocans vomeris, Crane 1975.

Vomeris comes from the Latin word vomer, meaning a ploughshare, or shaped like a wedge.

Further Reading:

Bennett, I. (1987). W. J. Dakin's classic study: Australian Seashores: a guide to the temperate shores for the beach-lover, the naturalist, the shore-fisherman and the student. p.232, Angus & Robertson.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.66. 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.70-74.

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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Images and Multi-media:  
Attached Image  
image/jpeg 85326 bytes Orange-clawed Fiddler Crab
Distribution Map  
image/gif 986 bytes Distribution of Orange-clawed Fiddler Crab

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