The Blunt Cockle

Lunulicardia retusa

Triangular outline, tending to ovate, more so than L. hemicardium, with a pronounced umbonal keel, which delineates a broad, rather flat or concave posterior. Posterior margin nearly vertical. Sculpture of ribs is low, interstices are pitted or crossed by raised transverse bars. With a wide lunule that is deeply impressed in contrast to L. hemicardium. Shells white in color internally and externally, with light red (rarely yellow) spots or blotches especially anteriorly. Thin yellow periostracum. Coloration of tissue brown due to presence of photosymbionts entrained in tissue.

Morphology

Photosymbiotic.

Evolution

This is the type species of the genus Lunulicardia. 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.

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:	retusa

Name Published Year:	1767
Rank:	species
Scientific Name Authorship:	Linnaeus
Commercial Impact:	Sought after by shell collectors
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-retusa
Accessed 7 Jul 2025

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References

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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 3: N-Z. Phuket Marine Biological Center Special Publication, 30, 645-939.

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. Lamy, E. (1942). Notes sur les espèces Lamarckiennes de Cardium. Bulletin du Muséum National d'Histoire Naturelle, Paris, (3)14(2nd series), 228-232 .

Odhner, N.H. (1919). Contribution à la faune malacologique de Madagascar. Arkiv för Zoologi, 12(6), 1-52.

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 (pl. 19, fig. 100, as C. subretusum; pl. 19, fig. 103 as C. retusum).

Satyamurti, S.T. (1956). Mollusca of Krusadai Is. II. Scaphopoda, Pelecypoda, and Cephalopoda. Bulletin of the Madras Government Museum, Natural History, ns1(no. 2, pt 7), 202.

Shuto, T. (1971). Neogene bivalves from Panay Island, the Philippines. Memoires of the Faculty of Science, Kyushu University, 21(1), 1-73.

Wells, F.E., & Bryce, C.W. (1986). Seashells of Western Australia. Perth, Western Australia: Western Australian Museum.

Wilson, B.R., & Stevenson, S.E. (1977). Cardiidae (Mollusca, Bivalvia) of Western Australia. Western Australian Museum Special Publication, 9, 1-114.