Fragum erugatum

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Fragum erugatum
Shell Beach Western Australia.jpg
Empty cockle shells on Shell Beach
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Heterodonta
Order: Cardiida
Family: Cardiidae
Genus: Fragum
Species:
F. erugatum
Binomial name
Fragum erugatum
(Tate, 1889)
Synonyms [1]
  • Cardium erugatum Tate, 1889
  • Cardium iranjanense Fischer-Piette, 1977
  • Cardium levisulcatum E. A. Smith, 1903
  • Fragum erugatum Tate, 1889
  • Fragum hamelini Iredale, 1949

Fragum erugatum is a small species of 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.

Contents

Taxonomy

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. [1]

Description

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. [2]

Distribution and habitat

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. [2] 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. [2] 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. [3]

Biology

Microfragum erugatum lives buried just below the sandy seabed, extending its siphons to the surface to draw in water in order to breathe and feed. It has symbiotic zooxanthellae in its mantle and gill tissues. These microalgae are photosynthetic and transfer simple organic compounds to their mollusc host which it uses to supplement the planktonic particles it filters from the water. This is a similar feeding strategy to that employed by the related giant clams (Tridacninae) which also contain symbiotic algae. In the clams this strategy is so successful that their shells become stronger, they have long lives and are able to grow to a very large size. By contrast, in Fragum erugatum, the molluscs remain small but thrive, becoming very numerous, sometimes being found at densities of 4,000 per square metre (11 sq ft). They are found subtidally at depths of between 1.2 and 6.5 metres (3 ft 11 in and 21 ft 4 in). Their lifespan may be just one year. [4]

Microfragum erugatum is a synchronous hermaphrodite. There seems to be a single spawning event each year with the cohort of juveniles being all the same age. [5] The gametes are liberated into the sea where the eggs are fertilised. The larvae form part of the zooplankton and drift with the currents until they settle on the seabed to undergo metamorphosis into juveniles. [6]

Related Research Articles

Bivalvia class of molluscs

Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. Bivalves as a group have no head and they lack some usual molluscan organs like the radula and the odontophore. They include the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances.

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Cockle (bivalve) Family of edible marine bivalve molluscs

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Coquina A sedimentary rock that is composed mostly of fragments of shells

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Giant clam species of clam

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<i>Donax</i> (bivalve) genus of molluscs

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Maxima clam species of clam

The maxima clam, also known as the small giant clam, is a species of bivalve mollusc found throughout the Indo-Pacific region. They are much sought after in the aquarium trade, as their often striking coloration mimics that of the true giant clam; however, the maximas maintain a manageable size, with the shells of large specimens typically not exceeding 20 centimetres (7.9 in) in length.

<i>Tridacna derasa</i> species of mollusc

Tridacna derasa, the southern giant clam or smooth giant clam, is a species of extremely large marine clam in the family Cardiidae.

Shell Beach (Western Australia) human settlement in Western Australia

Shell Beach is a beach in the Shark Bay region of Western Australia, located 45 km (28 mi) south-east of Denham.

Tridacninae family of molluscs

Tridacninae, common name, the giant clams, is a taxonomic subfamily of very large saltwater clams, marine bivalve molluscs in the family Cardiidae, the cockles.

<i>Donax variabilis</i> Species of mollusc

Donax variabilis, known by the common name coquina, is a species of small edible saltwater clam, a marine bivalve mollusc in the family Donacidae, the bean clams. It is a warm water species which occurs in shallow water on sandy beaches.

<i>Corculum cardissa</i> species of mollusc

Corculum cardissa, the heart cockle, is a species of marine bivalve mollusc in the family Cardiidae. It is found in the Indo-Pacific region. It has a symbiotic relationship with dinoflagellates (zooxanthellae), which live within its tissues.

<i>Fragum</i> genus of molluscs

Fragum is a genus of cockles, marine bivalve molluscs in the family Cardiidae. Members of the genus have characteristic thick, sculptured shells and live buried in sand, extending their siphons to the surface to feed and breathe. They are found in the Indo-Pacific region and the Red Sea.

<i>Fragum unedo</i> species of mollusc

Fragum unedo is a species of cockle, a marine bivalve mollusc in the family Cardiidae, commonly known as the Pacific strawberry cockle. It is found in tropical seas in the Indo-Pacific region and the empty shells are prized for use in decorative crafts.

<i>Cerastoderma glaucum</i> species of mollusc

Cerastoderma glaucum, the lagoon cockle, is a species of saltwater clam, a marine bivalve mollusc in the family Cardiidae, the cockles.

<i>Dinocardium</i> genus of molluscs

Dinocardium is a genus of large saltwater clams or cockles, marine bivalve molluscs in the family Cardiidae, the cockles. There is only one species in the genus, Dinocardium robustum, or the Atlantic giant cockle.

Fragum fragum is a species of cockle, a marine bivalve mollusc in the family Cardiidae. It is commonly known as the white strawberry cockle and is found in the western Indo-Pacific Ocean. It is the type species of the genus Fragum.

<i>Cassiopea xamachana</i> species of cnidarian

Cassiopea xamachana, commonly known as the upside-down jellyfish, is a species of jellyfish in the family Cassiopeidae. It is found in warm parts of the western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. It was first described by the American marine biologist Henry Bryant Bigelow in 1892.

<i>Acanthocardia echinata</i> species of mollusc

Acanthocardia echinata, the prickly cockle or European prickly cockle, is a species of saltwater clams, marine bivalve molluscs in the family Cardiidae. The genus Acanthocardia is present from the Upper Oligocene to the Recent.

Fragum nivale is a species of cockle in the family Cardiidae, that lives in the Western Indian Ocean, in benthic environments. It has a body length of 1.2 cm, and the embryos are developed into a swimming trocophore larvae, that resemble an immature clam.

References

  1. 1 2 ter Poorten, Jan Johan (2012). "Microfragum erugatum (Tate, 1889)". WoRMS. World Register of Marine Species . Retrieved 2013-03-25.
  2. 1 2 3 "Hamelin Cockle (Fragum erugatum)" (PDF). Shark Bay. Government of Western Australia: Department of Conservation and Environment. 2010. Archived from the original (PDF) on 2012-03-20. Retrieved 2013-03-26.
  3. "Nature of Shark Bay". Shark Bay World Heritage Area. SharkBay.org. Retrieved 2013-03-26.
  4. Morton, Brian (2000). "The biology and functional morphology of Fragum erugatum (Bivalvia: Cardiidae) from Shark Bay, Western Australia: the significance of its relationship with entrained zooxanthellae". Journal of Biology. 251 (1): 39–52. doi:10.1017/s0952836900005069.
  5. Berry, P. F.; Playford, P. E. (1997). "Biology of modern Fragum erugatum (Mollusca, Bivalvia, Cardiidae) in relation to deposition of the Hamelin Coquina, Shark Bay, Western Australia". Marine & Freshwater Research. 48 (5): 415–420. doi:10.1071/MF97005.
  6. Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology . Saunders College Publishing. p.  682. ISBN   978-0-03-030504-7.