Common Name: Semaphore Crab

Distribution: Abundant in the Solitary Islands Marine Park. In Australia recorded from southern Queensland through New South Wales and Victoria to Tasmania.

Ecological Notes: Frequents intertidal mudflats where it excavates a vertical burrow, which it retreats to when threatened.

Additional Notes: A robust small crab, the carapace is dark purple to black, the claws of near equal size and coloured purple in adults, orange in juveniles as in these images. As the tide recedes this small crab emerges from its burrow and rolls the soft mud or sand substrate into balls, removing detritus, alga or vegetable matter on which it feeds. Has been used in Queensland as an indicator of the health of an estuary by measuring the amount of toxins in its tissues, obtained from the substrate on which it feeds. Grows to a carapace width of around 25 mm.

References: Graham J. Edgar. Australian Marine Life, 2nd Edition, 2008. Reed New Holland Publishers. p.253.

Davie, Peter. Wild Guide to Moreton Bay and Adjacent Coasts. Second Edition. Published by Queensland Museum. Vol 2, p.247.