Strawberry Heart Cockle
Fragum unedo
Shell solid and inequilateral, umbonal keel rounded, subquadrate to trapezoidal with strongly digitate posterior margin. No strong keel. Strong broad, flat radial ribs ranging from 23 to 31, mean 27. Lunule narrow, smooth with raised dorsal margin. Escutcheon broad, smooth. Exterior white, ribs with irregular, transverse red scales, sometimes with pale brown blotches; interior white. It is distinct from all other fragines by the prominent red scales on the ribs of the shell. Shell length and width to around 5 cm while depth to above 6 cm.
Morphology
This is the most heavily bodied, heavily shelled species of the subfamily Fraginae. In contrast to Corculum that has a very light, thin and transparent shell (in areas), this species also participates in photosymbiosis but in a very different manner. Soft anatomy is not contained within the shell but is exposed as highly distinct leaf-like extensions of the posterior siphonal area, similar to but unique from the hypertrophied mantle of giant clams. These are spread out on the surface of the sediment and function to greatly increase surface area for photosymbionts that are contained within the exposed tissue.
Evolution
Kirkendale (2009) has shown (and others have confirmed e.g. Herrera et al. 2015) that Fragum is paraphyletic and includes Corculum and Lunulicardia, the two other wholly photosymbiotic lineages of cardiids.The phylogeny of members of the Fraginae subfamily is in a state of flux and the taxonomy of the group is in need of attention
Behaviour
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
Broadcast spawner.
Habitat
Marine
Intertidal to shallow subtidal in sandy areas. Generally in sheltered areas.
Distribution
QLD, NT and WA in Australia, but widely distributed in the Indo-west Pacific. Wilson and Stevenson 1977 note that placement of red scales appears different than in F. unedo from the Pacific ocean and Philippines.
Life Cycle
Short lived veliger larvae
Kingdom: | Animalia |
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Phylum: | Mollusca |
Class: | Bivalvia |
Subclass: | Heterodonta |
Superorder: | Imparidentia |
Order: | Cardiida |
Superfamily: | Cardioidea |
Family: | Cardiidae |
Subfamily: | Fraginae |
Genus: | Fragum |
Species: | unedo |
Name Published Year: | 1758 |
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Rank: | species |
Scientific Name Authorship: | Linnaeus |
Commercial Impact: | Sought after by shell collectors, possibly commercially exploitable (WS1977) |
Conservation Assessment: | Least Concern |
Cite this page
Western Australian Museum Collections https://museum.wa.gov.au/online-collections/names/fragum-unedo
Accessed 13 Aug 2024
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