species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of saltwater clam, a
marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
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 ...
Laternulidae, the lantern shells. It is the largest bivalve found under the surface of the seabed in the
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
Phillip Parker King
Rear Admiral Phillip Parker King, FRS, RN (13 December 1791 – 26 February 1856) was an early explorer of the Australian and Patagonian coasts.
Early life and education
King was born on Norfolk Island, to Philip Gidley King and Anna Jo ...
, and the English naturalist,
William Broderip
William John Broderip FRS (21 November 1789 – 27 February 1859) was an English lawyer and naturalist.
Life
Broderip, the eldest son of William Broderip, surgeon from Bristol, was born at Bristol on 21 November 1789, and, after being educat ...
, having been discovered during the first exploration of the
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
n coastline in
HMS Beagle
HMS ''Beagle'' was a 10-gun brig-sloop of the Royal Navy, one of more than 100 ships of this class. The vessel, constructed at a cost of £7,803 (roughly equivalent to £ in 2018), was launched on 11 May 1820 from the Woolwich Dockyard on th ...
. The title of the paper they published read "''Description of Cirrhipedia,
Conchifera
Conchifera is a subphylum of the phylum Mollusca. It comprises all of the shell-bearing classes of molluscs, such as clams, tusk shells, ammonites, and monoplacophorans. The other subphylum is Aculifera.
Non-monoplacophoran conchiferans emerged ...
and
Mollusca
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 a collection formed by the officers of H.M.S. Adventure and Beagle employed between the years 1826 and 1830 in surveying the southern coasts of South America, including the Straits of Magalhaens and the coast of
Tierra del Fuego
Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla G ...
.''"
Description
The shell of ''Laternula elliptica'' is thin, brittle, and slightly inflated and grows to a length of . The left valve is slightly larger and more convex than the right. The general shape is an elongated oval with the posterior end somewhat truncated and narrower than the anterior end. The umbone is shallow and slightly nearer the posterior end and there is a characteristic short transverse crack in it. The internal ligament is supported by a diagonal ridge of shell and there are no teeth near the hinge. The exterior of the shell is white, slightly granular and sculptured with fine concentric lines. The interior of the shell is somewhat
nacre
Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent.
Nacre is f ...
ous, with two adductor muscle scars and a pallial line that is slightly concave at the anterior end and has a broad pallial sinus at the posterior end. There is a gape at both ends of the shell and a pair of long siphons emerge from the posterior end being fused for their full length. The mantle margins are also fused apart from a small gap at the anterior end and the foot is small.
Distribution and habitat
''Laternula elliptica'' is found in the Southern Ocean, round
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
and the tip of
Patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
. It has been found in waters as shallow as the
intertidal zone
The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
and as deep as the
continental slope
A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...
(~), but it is most common in shallow waters. It is found living in soft substrates such as muddy sand and gravel in which it burrows deeply. It is sometimes found in densities of upward of 100 individuals per square metre.
Biology
Like other members of the family Laternulidae, ''Laternula elliptica'' is a
filter feeder
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...
. It lies beneath the substrate with its siphons extended to the surface. Water is drawn in through the inhalant siphon by a pumping action of the gills. As it passes over the gill flaps, gaseous exchange takes place and
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and
detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
are captured by
cilia
The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...
and moved in a flow of
mucous
Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...
to the mouth. The water then emerges through the exhalant siphon.
''Laternula elliptica'' is a
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 ...
. Fertilisation is external and epidemic
spawning
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquati ...
events sometimes occur. These greatly increase the concentration of gametes in the water and raises the rate of successful fertilisation of eggs. The embryos are
lecithotrophic
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and mo ...
and the
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
e remain inside the egg capsules and feed on the yolks of the eggs for some months before hatching direct into juveniles and settling on the seabed.
The concentric sculptured lines on the shell have been shown by radioactive carbon and oxygen dating to occur annually and have been used to tell the age of the animal. It has been found to live for up to twenty years.
Fossil record
Fossils of ''Laternula elliptica'' dating back to the late
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Cockburn Island and the
James Ross Island
James Ross Island is a large island off the southeast side and near the northeastern extremity of the Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north–south ...
group off the
Antarctic Peninsula
The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...
. Some of these fossils are still in the positions the molluscs occupied when alive and it has been found that they are all orientated in roughly the same direction, many with a variance of only 10° and all within a 66° range. This orientation is similar to the way in which the
soft-shell clam
Soft-shell clams (American English) or sand gaper (British English/Europe), scientific name ''Mya arenaria'', popularly called "steamers", "softshells", "piss clams", "Ipswich clams", or "Essex clams" are a species of edible saltwater clam, a ...
(''Mya arenaria'') places itself at right angle to the main water movements it experiences, a positioning that is believed to optimise water flow through the siphons. Another bivalve, the
freshwater pearl mussel
The freshwater pearl mussel (''Margaritifera margaritifera'') is an endangered species of freshwater mussel, an aquatic bivalve mollusc in the family Margaritiferidae.
Although the name "freshwater pearl mussel" is often used for this species ...
(''Margaritifera margaritifera''), is not exposed to the ebb and flow of the tide and locates itself so that the inhalant siphon is upstream of the exhalant siphon. This
rheotaxis
(Positive) Rheotaxis is a form of taxis seen in many aquatic organisms, e.g., fish, whereby they will (generally) turn to face into an oncoming current. In a flowing stream, this behavior leads them to hold their position rather than being swept do ...
may help ''Laternula elliptica'' maximise energy gain in the summer in an environment where the food availability and consequent growth of organisms varies greatly at different times of the year. The orientation of modern ''Laternula elliptica'' has not yet been studied.