Southern Sentinel Crab
The Southern Sentinel Crab has a very restricted distribution in south-eastern Australia. It is found on sand and mud flats of Victoria and gulf coasts of South Australia. Interestingly, an isolated population occurs at Port Hunter, central New South Wales. It is possible that this population has been introduced accidentally from Victoria. (NSW, VIC, SA)
The eyes stalks of the Southern Sentinel Crab are not as long as those of its northern relatives, though each is about one third the width of carapace. However, the eye orbits occupy the whole of anterior margin of the carapace, apart from the frontal section. The carapace is about 20 mm wide and some 13 mm long, and is covered in fine granules. Two teeth lie on the edge of the carapace behind the orbital tooth. The claws of the male are much larger and more robust. The immovable finger of the claw points downwards, and both fingers of each claw curve inwards; this may help to scoop up detritus and other food particles, which then can be extracted by the mouthparts. The walking legs are fringed with long hairs, and dense patches of fur are present on the second and third pairs of legs. The Southern Sentinel Crab is yellowish-brown in colour.
Ecology/Way of Life:
Southern Sentinel Crabs occur in sand and mud estuaries where they burrow in soft mud amongst seagrass. They emerge as the tide recedes and begin to feed on decomposing seagrass and other edible material on the exposed mudflats. Small pellets of mud are scooped up using the open fingers of the claws. These pellets are then transferred to the mouth where the maxillipeds (mouthparts) receive them and extract the edible matter. These crabs are almost always on the move. However, they are wary of moving too far from their burrow in case predators, such as wading birds, appear. They maintain their burrow continuously, excavating mud and heaping it several centimeters away from the mouth of the burrow. This species does not appear to plug its burrow. These crabs defend their burrow, standing quite still for long periods in the sun, despite drying out in the process, and hold their chelipeds and claws in front of their face. When fighting, the two crabs approach and cross over their chelipeds and claws, then move the claws out until they touch those of the other crab - after tapping them together, one crab sinks to the ground and retreats. Thee courtship display begins with the claws of the male held in front of the face; he then tips his body back, raises his claws up high then lets them fall, and repeats this "wave" up and down several times.
Interaction with Humans/Threats:
The Southern Sentinel Crab may have been introduced into the Hunter River estuary from its normal habitat in Port Phillip Bay, Vic., so it may have the potential to be an invasive species, particularly as its normal range is quite restricted.
Macrophthalmus latifrons was described by Prof. William A. Haswell in 1881; this species was formerly placed in the genus Hemiplax. The genus Macrophthalmus is from the Greek: makros = long; ophthalmos = eye, referring to the elongate eye stalks in this genus; the species name is from the Latin: latus = flank or side and frons = front, probably in relation to the position of the eye sockets.
Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.63, New Holland Press, Sydney.
Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p.217, Reed.
Hale, H.M. (1976). The Crustaceans of South Australia, Pts: I & II. p.186, The Government Printer, South Australia.
Jones, D. & Morgan, G. (1994). A Field Guide to Crustaceans of Australian waters. Reed.
Text, map & photograph by Keith Davey.
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