Fragum erugatum
| Fragum erugatum | |
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| Empty cockle shells on Shell Beach | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Bivalvia |
| Order: | Veneroida |
| Family: | Cardiidae |
| Genus: | Fragum |
| Species: | F. erugatum |
| Binomial name | |
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Fragum erugatum (Tate, 1889) |
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| Synonyms | |
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Fragum erugatum is a species of small cockle, a marine bivalve mollusc in the family Cardiidae. It is found in the shallow seas off the coast of Western Australia. It is commonly known as the Hamelin cockle, cardiid cockle or heart cockle.
This species was first described by Ralph Tate in 1889 as Fragum erugatum. More recently, it has been given several other names but these have since been synonymized with Fragum erugatum. Some authorities now consider that it is sufficiently distinct from other members of the genus Fragum as to warrant being placed in a genus of its own as Microfragum erugatum.
Fragum erugatum is a small species of cockle growing to a length of about 14 mm (0.6 in). The valves are dome-shaped, white and translucent.
Fragum erugatum is native to warm shallow waters in Western Australia. Its range extends from the Dampier Archipelago to the Houtman Abrolhos Islands near Geraldton. It is particularly prevalent in Shark Bay, a large lagoon with sandy flats and extensive seagrass meadows. One particular beach there is called Shell Beach because it is completely composed of the empty shells of this cockle, dumped on the shore during storms. Such beaches extend for 60 kilometres (37 mi) along the coast in belts which may be a kilometre wide. Further inland, ancient cockle shell deposits have become consolidated into a type of limestone known as coquina. The waters of Shark Bay are particularly saline, with up to twice the amount of dissolved salt as the open ocean. This is because of the shallow water, the restricted movement of water caused by sandbanks and seagrass beds and the high rate of evaporation. Fragum erugatum seems to thrive under these conditions.
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