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Halicarcinus ovatus (Family Hymenosomatidae)

Three-pronged Sea-Spider


Three-pronged, or Oval Spider-crabs occur in south-eastern and southern Australia, from Port Stephens in New South Wales, southwards around Victoria and Tasmania, to South Australia and southern Western Australia. (NSW, VIC, TAS, SA, WA)


This small, distinctively shaped crab has a long, narrow beak-like rostrum, which extends forwards from the carapace between the eyes. There are no eye notches. The smooth carapace is flat or slightly concave on top, oval and crossed by fine grooves. These crabs grow to about 13 mm in length. These crabs are boldly coloured in various combinations of red and white, brown and white or black and red. Males can be distinguished from females by their distinctly larger claws. The long thin legs, like those of a spider, give this crab its common name.

Ecology/Way of Life:

These crabs are found often at low tide levels in seagrass beds or sheltering under rocks and among algae on algal-covered rocky shores. They may also be abundant in estuarine seagrass beds and flats, and they enter fresh water in the upper reaches of the estuary. Little is known of their way of life. They are generally thought to be scavengers, but they may prey on small animals. They are eaten by several species of bottom-feeding fishes.

Interaction with Humans/Threats:

No direct threats on these crabs have been identified; potential threats include loss of habitat, or changes to the habitat, such as siltation or pollution.

Other Comments:

Halicarcinus ovatus was described by William Stimpson in 1858; the genus name comes from the Greek halios = of the sea, and carcinus = crab; the species name is from the Latin ovatus = oval or egg-shaped.

Further Reading:

Bennett, I. (1987). W.J. Dakin's classic study: Australian Seashores. P. 229, Angus & Robertson.

Davey, K. (1988). A Photographic Guide to Seashore Life of Australia. P. 48. New Holland Press.

Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. P. 208, Reed Books.

Hale, H.M. (1876). The Crustaceans of South Australia. Pts. I & II. South Australian Government Press, 117 pp.

Griffin, D.J.G. & Yaldwyn, J.C. (1971) Port Phillip survey 2, Part 5: Brachyura (Crustacea, Decapoda). Memoirs of the National Museum of Victoria 32: 43-63.

Jones, D. & Morgan, G. (1994). A Field Guide to Crustaceans of Australian Waters. Reed Books, 153 pp.

Lucas, J.S. (1980) Spider crabs of the family Hymenosomatidae Australian species; systematics and biology. Memoirs of the National Museum of Victoria 33(4): 148-247.

Marine Research Group of Victoria. (1984). P. 111, Coastal Invertebrates of Victoria: an atlas of selected species. Museum of Victoria.


Text, map & photograph by Keith Davey.

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