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Mictyris platycheles (Family Mictyridae)

Dark-blue Soldier Crab


The Dark-blue Solder Crab has a south-eastern Australian distribution. It ranges from Moreton Bay, Qld, through NSW, south to Port Phillip Bay, Vic, and Tas (QLD, NSW, VIC, TAS).


The Dark-blue Soldier Crab is a distinctive, globe-shaped, dark-blue and grey soldier crab, with a prominent purple and white bulge on each side towards the rear. It grows to 12-15 mm in size, which is half the size of its relation the Light Blue Soldier Crab. The Dark-blue Soldier Crab has long, thin legs and flattened feeding chelipeds. It does not have dark patches on its leg joints like the Light Blue Soldier Crab, M. longicarpus. The sexes are similar, and unlike most other crabs, its abdominal flap is almost as wide as occurs in females.

Ecology/Way of Life:

The Dark-blue Soldier Crab occurs on estuarine flats where the sand flats gradually become mudflats. It only forms large feeding groups on southern Australian shores. Its relation, the Light Blue Soldier Crab, M. longicarpus, is more common on northern shores.

The Dark-blue Soldier Crab processes large amounts of sand to extract micro-algae and detritus food. It leaves processed sand as round pellets. If disturbed, the Dark-blue Soldier Crab rapidly buries into sediment in spiral manner. It does not form permanent burrows, but buries itself into the sediment when it feels threatened, or when it is finished feeding and the tide is returning. The Soldier Crabs are the only crabs that can walk forwards rather than sideways. This is possible because of the structure and placement of its legs.

Interaction with Humans/Threats:

Because this species occurs in estuaries, many of which are ports, there is some risk from pollution caused by human activities. As well, it has a reasonably limited distribution range limited to south-eastern Australia.

Other Comments:

Mictyris platycheles, Milne Edwards, 1852. Mictyris may come from the Latin word micturire, which means the desire to urinate, while platycheles comes from two Greek words. Platy means broad, while cheles comes from chele that means a crab's claw.

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.228, Angus and Robertson.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.68, New Holland Press, Sydney.

Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p.217, Reed.

Jones, D. and Morgan, G. (1994). A Field Guide to Crustaceans of Australian waters. p.192, Reed.

Marine Research Group of Victoria (1984). Coastal Invertebrates of Victoria: An atlas of selected species. p.125, Museum of Victoria.


Text, map and photograph by Keith Davey.

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