Lunulicardia hemicardium from Shark Bay, WA (Photo: Lisa Kirkendale)
Lunulicardia hemicardium from Shark Bay, WA (Photo: Lisa Kirkendale)

Half Heart Cockle

Lunulicardia hemicardium

Shell medium to large (H35-65 mm), with pronounced umbonal keel, which delineates a broad, flat posterior. Sculpture of ribs is low, interstices are narrow. Mean total number of ribs  23, range 18-27 (Shark Bay population). Hinge strongly bent but not distorted, with a wide lunule that is not impressed (in contrast with often sympatric congener, L. retusa). Shell is white in color internally and externally. Coloration of tissue brown due to presence of photosymbionts entrained in tissue. Length 4.76 cm, height 6.84 cm and width 5 cm (Shark Bay population).

Morphology

Paedomorphic development (Ter poorten 2009). Photosymbiotic.

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.

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

Marine, intertidal to shallow subtidal.

Distribution

QLD, NT and WA in Australia, but widely distributed in the Indo-west Pacific. Some suggestion that morphological distinction exists for WA populations (Wilson and Stevenson 1977, pg. 42), for which name L. tumoriferum exists (Lamarck, 1819). Revisiting these earlier findings and incorporating appropriate genetic markers to test this hypothesis are required.

Life Cycle

Short lived veliger larvae.

Taxonomy

Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Heterodonta
Superorder: Imparidentia
Order: Cardiida
Superfamily: Cardioidea
Family: Cardiidae
Subfamily: Fraginae
Genus: Lunulicardia
Species: hemicardium
Name Published Year: 1758
Rank: species
Scientific Name Authorship: Linnaeus
Commercial Impact: 

Sought after by shell collectors, possibly commercially exploitable (WS1977)

Conservation Assessment: Least Concern

Net Conservation Benefits Fund

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Western Australian Museum Collections https://museum.wa.gov.au/online-collections/names/lunulicardia-hemicardium
Accessed 14 May 2024

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References

Allan, J.K. (1950). Australian Shells: with related animals living in the sea, in freshwater and on the land. Melbourne, Victoria: Georgian House (as Hemicardium hemicardium).

Coleman, N. (1975). What Shell is That?. Sydney: Lansdowne Press.

Cotton, B.C. (1964). Molluscs of Arnhem Land. Records of the American-Australian Scientific Expedition to Arnhem Land, 4 (Zoology), 9-43 (as H. tumoriferum).

Dufo, M.H. (1840). Observations sur les Mollusques marins, terrestres et fluviatiles des iles Séchelles et des Amirantes. Annales des Sciences Naturelles, Paris, 2 14, Zoologie, 45-80 (extrait), 166-221(suite) .

Huber, M. (2010). Compendium of Bivalves. A full-color guide to 3,300 of the world’s marine bivalves. A status on Bivalvia after 250 years of research. Hackenheim, Germany: ConchBooks (as forma tumoriferum for Australia).

Hylleberg, J. (2004). Lexical approach to Cardiacea. Records of taxa. Illustrated and annotated records of living and fossil shells, with emphasis on the families Cardiidae and Lymnocardiidae (Mollusca: Bivalvia). Part 2: A-M. Phuket Marine Biological Center Special Publication, 30, 355-644.

Kirkendale, L. (2009). Their Day in the Sun: molecular phylogenetics and origin of photosymbiosis in the ‘other’ group of photosymbiotic marine bivalves (Cardiidae: Fraginae). Biological Journal of the Linnean Society of London, 97, 448–465.

Lamprell, K., & Whitehead, T. (1992). Bivalves of Australia. Vol. 1. Bathhurst, New South Wales: Crawford House Press.

Oliver, P.G. (1992). Bivalved Seashells of the Red Sea. Wiesbaden: Verlage Christa Hemmen.

Reeve, L.A. (1844). Monograph of the genus Cardium. pls 1-12, 13-22 In Reeve, L.A. (ed.). Conchologica Iconica. Vol. 2. London: Reeve & Bentham (as C. hemicardium, pl. 12, fig. 64 as C. tumoriferum).

Rippingale, O.H., & McMichael, D.F. (1961). Queensland and Great Barrier Reef Shells. Brisbane, Queensland: Jacaranda Press (as Hemicardium hemicardium).

Wells, F.E., & Bryce, C.W. (1986). Seashells of Western Australia. Perth : Western Australian Museum. Wilson, B.R., & Stevenson, S.E. (1977). Cardiidae (Mollusca, Bivalvia) of Western Australia. Western Australian Museum Special Publication, 9, 1-114.