Shell small to medium, highly variable in form from rounded sub-trapezoidal to obliquely quadrate. Margins serrate and umbos prosogyrate, not central but offset. Sculpture simple of broad, round, flat ribs mean 25 with range 24-28 (Shark Bay population). Largest shell measured 1.74 cm length, 1.88 cm height, 0.90 cm width (Wilson and Stevenson 1977). Shell is white with tinges of yellow or pink in interior, sometimes slightly translucent. Coloration of tissue brown due to presence of photosymbionts entrained in tissue.
Placed in the genus Microfragum by some (which includes non-photosymbiotic species), however molecular phylogenetics place it firmly as one of the paraphyletic and wholly photosymbiotic species of the genus Fragum.
All cockles or cardiids have short siphons. Because of this morphological constraint, infaunal cardiids live close to the sediment water interface in order to filter water. This could be considered a preadaptation for a photosymbiotic lifestyle, as it also facilitates optimal light penetration into the soft tissues in shell interior where photosymbionts are housed.
Method of reproduction
The species lives in dense populations on sandy bottoms to at least 9 metres in protected embayments.
Indian ocean species (Ter Poorten 2009). Type locality is in South Australia, where it is apparently only known as a fossil. Records in WA based on live collected material occur from Rosemary Island in Dampier Archipelago to as far south as the Abrolhos and Geraldton. Extensive populations occur in Shark Bay, Western Australia where the species occurs in huge quantities in hypersaline reaches of Hamelin Pool.
Short lived veliger larvae.
|Name Published Year:||1889|
|Scientific Name Authorship:||Tate|
Fossil information, coquina, links to website, used to make building blocks for houses (e.g. Telegraph in Hamelin Bight). As such, transported around the state so dead shell records are to be treated with suspicion. Found in my chickens feed!
|Conservation Assessment:||Least Concern|
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Western Australian Museum Collections https://museum.wa.gov.au/online-collections/names/fragum-erugatum
Accessed 28 Oct 2021
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