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Paragrapsus gaimardii (Family Grapsidae)

Mottled Shore Crab

Distribution:

The Mottled Shore Crab has a distribution range restricted to Vic, Tas and SA. Its distribution range overlaps with the Spotted Smooth Shore Crab, P. laevis, in Victoria. (VIC, TAS, SA)

Features:

The Mottled Shore Crab is distinguished by having a shallow notch on the carapace between its eyes, and having a pad of felt restricted to the underside of first walking leg, rather than having whole of second segment covered with felt, as found in Paragrapsus laevis. There are also differences in the shape of the blotches on the carapace. The common names "mottled" and "spotted" describe this difference.

The Mottled Shore Crab is a mid-sized shore crab that is similar in form to its northerly relation, the Spotted Smooth Shore Crab, Paragrapsus laevis. The female crabs of both species are very similar. It grows to 30-35 mm across the carapace.

The Mottled Shore Crab has a depressed body. It is almost rectangular in shape. Its carapace has a more rugged appearance and is more granulated than found in the Sun-clawed Crab, Helograpsus haswellianus. On the carapace, the front edge is bilobed. Its carapace margins are raised slightly and are beaded. Behind the eyes are two bumps, called teeth.

Adult male chelipeds (feeding claws) are very large. Above, they are dark red-purple and cream below. The outer surface of the hand is marked with fine granules; while the inner surface is more or less covered with larger granules, as well as a ridge made up of distinct bumps called tubercles.

In colour it has a sandy yellow to yellowish base colour above with dark red spots over all surfaces, giving it a dark to black appearance.

Ecology/Way of Life:

The Mottled Shore Crab is commonly found under rocks, under timber and sheets of roofing iron lying at the high tide level on the mud shores of rivers and mudflats of estuaries. They may be observed as they forage at night in shallow water.

Interaction with Humans/Threats:

Although the Mottled Shore Crab has a restricted range in south-eastern Australia, it is common where it occurs, and does seem to prefer to live in estuaries under debris that has been created by humans. Therefore, it probably is not threatened by human activities, except for an environmental disaster in a localised area such as a massive oil or chemical spill in an estuary.

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.231, Angus and Robertson.

Campbell, B. M. and Griffin, D. J. G. (1966). The Australian Sesarminae (Crustacea: Brachyura); Genera Helice, Helograpsus nov., Cyclograpsus and Paragrapsus. Memoirs of the Queensland Museum, 14(5), p.127-174.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.54, New Holland Press, Sydney.

Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p.213, Reed.

Griffin. D. J. G. and Yaldwyn, J. C. (1971). Port Phillip Survey 2, Part 5: Brachyura (Crustacea, Decapoda). Memoirs of the National Museum of Victoria, v.32, p.43-63. Jones, D. and Morgan, G. (1994). A Field Guide to Crustaceans of Australian waters. p.189, Reed.

Marine Research Group of Victoria (1984). Coastal Invertebrates of Victoria: An atlas of selected species.p.119, Museum of Victoria.

Acknowledgments:

Text, map and photograph by Keith Davey.

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