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Strombus urceus (Family Strombidae)

Pitcher-shaped Stromb, Scorpion Shell, Spider Shell

Distribution:

The Pitcher-shaped Stromb has an Indo-West Pacific distribution. In northern Australian it ranges from North West Cape, WA, across northern shores including the NT, to the Gulf of Carpentaria, Qld (WA, NT, QLD).

Features:

The Pitcher-shaped Stromb is a highly variable species. It has a solid shell with a high spire and a flaring, thick outer lip. It grows to a shell length of 50-60 mm. Its shell sculpture consists of thick, bumpy whorls. These bumps or nodules form a distinct shoulder that goes around the whorl the full length of the shell. Cords near the aperture lip cross the whorls. There is a notch on the lip of the shell through which the stalked right eye peeks. A U-shaped notch occurs near the rear of the shell. The heavy lip is square-shaped in the north Australian sub-species, S. u. orrae. It also has a shorter anterior canal and larger shoulder nodules.

Longitudinal axial ribs sometimes occur on the ventral side of the shell. The columella has callouses. The operculum is made of horn-like material and is lengthened and pointed like a blade. It is carried on the hind end of the muscular foot. The knife-shaped operculum is not large enough to cover the aperture, but can be used as a weapon or can be pushed into the substrate to move along, or turn back an overturned shell.

The shell exterior is cream, brown, white or greenish in colour with darker spiral lines, bands or blotches. Inside the shell is white, purple or black, merging to yellow, then white at the columella. Occasionally the columella may be black, or more rarely orange in colour.

Ecology/Way of Life:

The Pitcher-shaped Stromb occurs as groups on sand or mud substrates, at low tide levels and below to 40 metres. It is herbivorous and feeds on algae and detritus. Strombs can be quite difficult to see in their habitat as the shell is often covered with seaweed growths.

The tropical reef-living Strombs are some of the most active of the shelled molluscs. There are about 18 Stromb species living in the Great Barrier Reef area and range in size from 50 mm to 300 mm in length. They thrust their claw-like operculum into the sand and contract their muscular foot and move along in a series of jerks. Unlike most other molluscs, Strombs prefer to be out in the open on the reefs. The female Stromb lays long egg-masses that are coiled and twisted tubes of jelly covered with grains of sand. The eggs are tiny and numerous. Each egg mass may contain half a million eggs. The embryos hatch as free swimming veliger larvae (Wilson & Gillett, 1979).

Interaction with Humans/Threats:

The Pitcher-shaped Stromb is common across remote tropical Australian shores and is probably under no threat from human activities.

Other Comments:

Strombus (Canarium) urceus, Linnaeus, 1758. The northern Australian sub-species is S. urceus orre, Abbott, 1960.

Strombus comes from the Greek word Strombos, meaning a spinning-top, snail or whirlwind. Urceus is the Latin word for a liquid-holding pitcher.

Further Reading:

Bennett, I. (1971). The Great Barrier Reef. p.134, Lansdowne.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. New Holland Press, p.107, Sydney.

Reader's Digest Services. (1984). Reader's Digest Book of the Great Barrier Reef. p.185, Reader's Digest.

Short, J. W. & Potter, D. G. (1987). Shells of Queensland and the Great Barrier Reef. p.34, Golden Press.

Wells, F. E. & Bryce, C. W. (1988). Seashells of Western Australia. p.64, Western Australian Museum.

Wilson, B. (1993) Australian Marine Shells. Prosobranch gastropods. V.1. p.155, Odyssey Publishing.

Wilson, B. R. & Gillett, K. (1979). A Field Guide to Australian Shells: Prosobranch Gastropods. p,67, 73, Reed.

Acknowledgments:

Text, map & photograph by Keith Davey.

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