''Fragum erugatum'' is a small species of
cockle, a marine
bivalve
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. As a group, bival ...
mollusc
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...
in the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Cardiidae
A cockle is an edible marine bivalve mollusc. Although many small edible bivalves are loosely called cockles, true cockles are species in the family Cardiidae. MolluscaBase eds. (2022). MolluscaBase. Cardiidae Lamarck, 1809. Accessed through: W ...
. It is found in the shallow seas off the coast of
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
. It is commonly known as the Hamelin cockle, cardiid cockle or heart cockle.
Taxonomy
This species was first described by
Ralph Tate
Ralph Tate (11 March 1840 – 20 September 1901) was a British-born botanist and geologist, who was later active in Australia.
Early life
Tate was born at Alnwick in Northumberland, the son of Thomas Turner Tate (1807–1888), a teacher of math ...
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''.
[
]
Description
''Fragum erugatum'' is a small species of cockle growing to a length of about . The valves are dome-shaped, white and translucent.
Distribution and habitat
''Fragum erugatum'' is native to warm shallow waters in Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
. Its range extends from the Dampier Archipelago
The Dampier Archipelago is a group of 42 islands near the town of Dampier in the Pilbara, Western Australia.
The archipelago is also made up of reefs, shoals, channels and straits and is the traditional home of five Aboriginal language group ...
to the Houtman Abrolhos Islands near Geraldton
Geraldton (Wajarri: ''Jambinu'', Wilunyu: ''Jambinbirri'') is a coastal city in the Mid West region of the Australian state of Western Australia, north of the state capital, Perth.
At June 2018, Geraldton had an urban population of 37,648. ...
. It is particularly prevalent in Shark Bay
Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
, a large lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...
with sandy flats and extensive seagrass meadow
A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...
s. 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.[ Such beaches extend for 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
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
known as coquina
Coquina () is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically sorted fragments of the shells of mollusks, trilobites, brachiopods, or other invertebrates. The term ''coquina'' ...
.[ 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.
]
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
Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
zooxanthellae
Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Sy ...
in its mantle and gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
tissues. These microalgae are photosynthetic
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
and transfer simple organic compounds to their mollusc host which it uses to supplement the plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
ic particles it filters
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component tha ...
from the water. This is a similar feeding strategy to that employed by the related giant clams (Tridacninae
Tridacninae, common name, the giant clams, is a Taxonomy (biology), taxonomic family (biology), subfamily of very large saltwater clams, marine (ocean), marine bivalve molluscs in the family Cardiidae, the cockles.
Description
This subfamily con ...
) 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 . Their lifespan may be just one year.
''Microfragum erugatum'' is a synchronous hermaphrodite
In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes.
Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...
. There seems to be a single spawning event each year with the cohort of juveniles being all the same age. The gametes are liberated into the sea where the eggs are fertilised. The larvae form part of the zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
and drift with the currents until they settle on the seabed to undergo metamorphosis
Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
into juveniles.
References
{{Taxonbar, from1=Q8565292, from2=Q13852956
Cardiidae
Molluscs described in 1889