The Coarse Cronia has a limited north-western tropical Australian distribution. It ranges from North West Cape, WA, across NT shores to the western edge of the Gulf of Carpentaria (WA, NT).
The Coarse Cronia has a shell that is oval to biconic (two cones end to end) in shape. It grows to 35 mm in length. Its shell sculpture consists of noduled whorls with angled shoulders and 6-8 distinct axial ribs that are crossed by numerous spiral fine-scaled cords. The aperture outer lip has 4-5 internal teeth-like bumps called denticles. The columella is smooth, or may have two very small denticles at the anterior or front end. The shell is often eroded, blurring its features.
The shells external colour is uniformly brownish black, with a lilac coloured columella and lip. This shell is similar to the Lustrous Cronia, C. margariticola, but is more biconic in shape, has fewer axial ribs and is less scaly, although their ranges do overlap across north-western Australia.
Ecology/Way of Life:
The Coarse Cronia occurs in Australia's most remote shores in north-western Australia, so little is known of its lifestyle and habits. At the family level Wilson states that almost all the thaids live in coral and rock habitats, many of them intertidal. They are carnivorous and actively hunt down and feed on barnacles, bivalves and other molluscs. It is likely that the Coarse Cronia is able to drill through the shell of its prey with its hardened radula tongue.
Interaction with Humans/Threats:
Although the Coarse Cronia has a distribution range limited to one quarter of the Australian coastline, it does occur in Australia's most remote coasts, away from human habitation.
We know little about the lifecycle of this species and it is probably only known from shell collections. Wilson (1993) states that some authors consider this to be a form of Cronia margariticola. However, the Coarse Cronia is more biconic, has fewer ribs and is less scaly than that species. Wilson goes on to suggest that further study is needed to determine if the two forms are ecologically separated because their distributions ranges overlap broadly in remote north-western Australia. Some authors, Wilson included, in 'Wilson, B. R. & Gillett, K. (1979). A Field Guide to Australian Shells: Prosobranch Gastropods', as well as Wells and Bryce (1988) have described C. margariticola as Morula margariticola, so it could be that this species might be Morula crassulnata. More research is required.
Cronia crassulnata, Hedley, 1914. Cronia may come from the Greek word chronios, meaning long continued or perennial. Crassulnata comes from two Latin words; crass, means thick, dense or stupid, and ulna means elbow or arm. The Greek word is olene, or forearm.
Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.112, New Holland Press, Sydney.
Wells, F. E. & Bryce, C. W. (1988). Seashells of Western Australia. p.92, Western Australian Museum,Perth.
Wilson, B. (1993) Australian Marine Shells. Prosobranch gastropods. Odyssey Publishing.
Wilson, B. R. & Gillett, K. (1979). A Field Guide to Australian Shells: Prosobranch Gastropods. p.156, Reed.
Text, map & photograph by Keith Davey 13/05/2002
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