species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
bivalve
Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
mollusc
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
in the
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
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 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...
Phillip Parker King
Phillip Parker King (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 Josepha King ''née'' Coo ...
, 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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
n coastline in HMS Beagle. The title of the paper they published read "''Description of Cirrhipedia,
Conchifera
Conchifera is a subphylum of the phylum Mollusca, containing five extant classes: Monoplacophora, Cephalopoda, Gastropoda, Bivalvia, and Scaphopoda. Conchiferans can bear a single shell as in snails and ammonites, a single pair of shell ...
and
Mollusca
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
, 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 Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South America, South American mainland, across the Strait of Magellan.
The archipelago consists of the main is ...
.''"
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 ...
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 (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
and the tip of
Patagonia
Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...
. It has been found in waters as shallow as the
intertidal zone
The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...
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 margi ...
(~), 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 aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...
. 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 Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...
and
detritus
In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...
are captured by
cilia
The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...
and moved in a flow of
mucus
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 fluid, serous and muc ...
to the mouth. The water then emerges through the exhalant siphon.
''Laternula elliptica'' is a
hermaphrodite
A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic.
The individuals of many ...
. Fertilisation is external and epidemic
spawning
Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...
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 and the
larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
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 (geology), epoch in the geologic time scale that extends from 5.33 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–so ...
group off the
Antarctic Peninsula
The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martin 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 Antarctica.
...
. 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 (''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 animal, aquatic bivalve mollusc in the family Margaritiferidae.
Although the name "freshwater pearl mussel" is often used fo ...
(''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
A stream is a continuous body of water, body of surface water Cu ...
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.