The Antarctic scallop (''Adamussium colbecki'') is a species of

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 large

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 ...

scallop Scallop () is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families ...

s, the

Pectinidae Scallop () is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families ...

. It was thought to be the only

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 ...

in the genus ''

Adamussium ''Adamussium'' is a genus of scallops belonging to the family Pectenidae from the Southern Ocean around Antarctica. There are three known species but only one is extant, the Antarctic scallop (''A. colbecki''). Of the two extinct species ''A. jo ...

'' until an extinct

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58described in 2016. Its exact relationship to other members of the Pectinidae is unclear. It is found in the ice-cold seas surrounding

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 ...

, sometimes at great depths. ''Adamussium colbecki'' is a large, slow-growing

that lives on the seabed. The

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard ou ...

consists of a pair of ribbed calcareous valves which enclose the soft body and are joined by a ligament at a hinge. It feeds on microscopic green algae and is sometimes present in great numbers. It is able to move around by flapping its valves and to dart backwards to escape threats. The species is an important member of the Antarctic

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

community as the upper valve often acts as a substrate for seaweeds, sponges and other organisms. In addition, juveniles bind themselves by threads to the upper valve of older shells, using these as a base for several years as they grow. The adult scallops have been used in research to study the accumulation of

heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...

in marine organisms.

Taxonomy

The Antarctic scallop was first described by the British zoologist

Edgar Albert Smith Edgar Albert Smith (29 November 1847 – 22 July 1916) was a British zoologist, a malacologist. His father was Frederick Smith, a well-known entomologist, and assistant keeper of zoology in the British Museum, Bloomsbury. Edgar Albert Smith w ...

in 1902 as ''Pecten colbecki''. He worked at the

British Museum The British Museum is a public museum dedicated to human history, art and culture located in the Bloomsbury area of London. Its permanent collection of eight million works is among the largest and most comprehensive in existence. It docum ...

and was responsible for examining and describing shells from collections made over the years that had been deposited there. The German malacologist Johannes Thiele determined in 1934 that the characteristics of the Antarctic scallop were sufficiently different from those of other members of the genus '' Pecten'' to warrant its inclusion in a separate genus, ''Adamussium''. More recently,

examinations An examination (exam or evaluation) or test is an educational assessment intended to measure a test-taker's knowledge, skill, aptitude, physical fitness, or classification in many other topics (e.g., beliefs). A test may be administered verba ...

of the

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

structure and of the

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

of ''A. colbecki'' have been undertaken, but the exact

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

relationship it has with other pectinids is still unclear. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

most likely honours William Colbeck, the

cartographer Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an im ...

and magnetic observer on the British Southern Cross Antarctic Expedition (1898–1900).

Description

The Antarctic scallop's shell grows to about long and 7 centimetres wide and has a nearly circular outline. The two purplish-red valves are paper thin and only slightly convex and are attached by a long, slightly sinuous, hinge. Near the hinge there is an umbo or beak on each valve, a raised hump from which the ribs radiate. The umbones are not very prominent and on either side of them are irregular winged processes, the auricles. In smaller specimens there are around 12 shallow ribs diverging from the umbones and further low ridges appear between these as the shell grows larger. There is a fine sculpturing of concentric lines on the outside of the valves. The auricles are also finely sculpted with the annual growth lines visible. The interior of the valves is pink. A fringe of numerous small tentacles project from the mantle between the two valves and there are a number of simple eyes in a row around the rim. The valves are held closed by powerful

adductor muscles The adductor muscles of the hip are a group of muscles mostly used for bringing the thighs together (called adduction). Structure The adductor group is made up of: *Adductor brevis *Adductor longus *Adductor magnus * Adductor minimus This is o ...

which work in opposition to an elastic ligament that lies just behind the umbones and which tends to open the valves. The flanges of the auricles provide a wide attachment for this ligament. The Antarctic scallop could be confused with other scallops, other bivalves or

lamp shells Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

.Mollusca: ''Adamussium colbecki''
CCAMLR VME Taxa Classification Guide(2009). Retrieved 2012-04-07.

Distribution and habitat

The Antarctic scallop is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the waters surrounding Antarctica. These are mostly within the Antarctic Circle and include the

Ross Sea The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who vi ...

, the

Weddell Sea The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha ...

, the

Davis Sea Davis Sea is an area of the sea along the coast of East Antarctica between West Ice Shelf in the west and the Shackleton Ice Shelf in the east, or between 82° and 96°E. The name "Davis Sea" appears in most leading geographically authoritati ...

McMurdo Sound McMurdo Sound is a sound in Antarctica. It is the southernmost navigable body of water in the world, and is about from the South Pole. Captain James Clark Ross discovered the sound in February 1841, and named it after Lt. Archibald McMurdo o ...

and 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 ...

. Although it is commonly found at depths of less than ,

remotely operated underwater vehicle A remotely operated underwater vehicle (technically ROUV or just ROV) is a tethered underwater mobile device, commonly called ''underwater robot''. Definition This meaning is different from remote control vehicles operating on land or in the ai ...

s armed with lights and cameras have recorded the scallop at much greater depths, including one recording at . It is found on many different substrates including sand, gravel and silt, either on the surface or semi-submerged in the sediment. It can flap its gills slightly to create a hollow in which to settle. In shallow waters it is usually attached by

byssus A byssus () is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilid ...

threads to hard surfaces so as not to be swept away by water movement. At greater depths it is usually free living. Although the Antarctic scallop has a circum-polar distribution, this is very disjunct, and overall it is not common. In some places it is found at densities of up to 90 per square metre and in

Terra Nova Bay Terra Nova Bay is a bay which is often ice free, about long, lying between Cape Washington and the Drygalski Ice Tongue along the coast of Victoria Land, Antarctica. It was discovered by the British National Antarctic Expedition (known as the ...

in the Ross Sea, at depths between and , some scallop beds were found to be so crowded that adult individuals were lying on top of others. In other locations that seem eminently suitable in many ways, it was entirely absent. A possible explanation for this lies in the fact that its paper thin shell is characteristic of bivalves living in stable, deep water areas with little water movement. The shallower locations in which it now thrives are characterised by being protected bays or by having extensive sea ice coverage, each of which provides a stable environment unaffected by storm waves and where

iceberg An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...

scouring does not normally occur. It is also absent from habitats dominated by other benthic suspension feeding communities whereas it is found in habitats with soft sediments and no dominant cnidarian and sponge communities. This might be because its larvae face such heavy predation in these locations that it is unable to establish itself.

Behaviour

Locomotion

The Antarctic scallop can swim rather slowly by opening and closing its valves. It advances in this way with the rim of the shell to the front. It can detect the movement of nearby objects with its rudimentary eyes and, in order to escape predators, can move much more swiftly umbones first, by clapping its valves shut. A remotely controlled camera stationed on the sea bed is apt to find that all the scallops that were originally in its field of view have moved off to other locations.

Feeding

Like other members of the family Pectinidae, the Antarctic scallop is a

suspension 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 ...

, extracting its nourishment from the sea water that surrounds it. Bands of cilia on the velum, a curtain-like fold of the mantle, waft particles towards the gills.

Oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

is absorbed by the gills and food particles, mostly microscopic algae, are trapped in

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 ...

and transported to the mouth 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 ...

. There is a seasonal increase in microscopic

ice algae Ice algae are any of the various types of algal communities found in annual and multi-year sea or terrestrial ice. On sea ice in the polar oceans, ice algae communities play an important role in primary production. The timing of blooms of the alg ...

which become available to suspension feeders when the sea ice melts in the summer, and most of the annual growth takes place at this time. Research has shown that this is as a result of the rise in sea temperature and not the greater availability of food.

Reproduction

The rate of growth of the Antarctic scallop is very slow compared to that of scallops living in warmer seas. It matures at 5 to 7 years old and spawning takes place in late summer. Little is known about the development of the

veliger A veliger is the planktonic larva of many kinds of sea snails and freshwater snails, as well as most bivalve molluscs (clams) and tusk shells. Description The veliger is the characteristic larva of the gastropod, bivalve and scaphopod ...

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 but they may be planktonic for 4 or 5 months. Besides feeding on

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 small

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 ...

, they may absorb dissolved organic matter and consume

bacterioplankton Bacterioplankton refers to the bacterial component of the plankton that drifts in the water column. The name comes from the Ancient Greek word ' ('), meaning "wanderer" or "drifter", and ', a Latin term coined in the 19th century by Christian G ...

. When they settle,

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 ...

takes place and the juveniles attach themselves with byssus threads, often attaching these to the upper valves of scallops, and remain attached for 3 to 5 years. While attached to the adult shell, the juveniles benefit from food particles in the fine

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 ...

thrown up into the water column by movements of the adult. While studying the sizes and growth rates of adults, researchers came to realize that there were gaps in their records which were due to the fact that, in some years, no juveniles had survived.

Ecology

The Antarctic scallop is monitored in connection with the Vulnerable Marine Ecosystems (VME) classification set up by the

Convention on the Conservation of Antarctic Marine Living Resources The Convention on the Conservation of Antarctic Marine Living Resources, also known as the Commission for the Conservation of Antarctic Marine Living Resources, and CCAMLR, is part of the Antarctic Treaty System. The convention was opened for s ...

(CCAMLR). As such, notification is required to be made by vessels that land the scallop as by-catch during their fishing activities. The Antarctic scallop is often found living in association with the Antarctic sea urchin, ''

Sterechinus neumayeri ''Sterechinus neumayeri'', the Antarctic sea urchin, is a species of sea urchin in the family Echinidae. It is found living on the seabed in the waters around Antarctica. It has been used as a model organism in the fields of reproductive biolo ...

'', and ''

Odontaster validus ''Odontaster validus'' is a species of sea star in the family Odontasteridae. Its range includes the Southern Ocean and the seas around the mainland and islands of Antarctica. Description ''Odontaster validus'' can grow to about 10 cm (4&n ...

'', a species of sea star. Predatory invertebrates found in the vicinity of the Antarctic scallop include the

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

Neobuccinum eatoni ''Neobuccinum eatoni'' is a species of sea snail, a marine gastropod mollusk in the family (biology), family Buccinidae, the true whelks. Description Distribution References

Buccinidae Gastropods described in 1875 {{Buccinidae-s ...

'', and the ribbon worm ''

Parborlasia corrugatus ''Parborlasia corrugatus'' is a proboscis worm in the family Cerebratulidae. This species of proboscis or ribbon worm can grow to in length, and lives in marine environments down to . This scavenger and predator is widely distributed in cold s ...

''. The foraging techniques of the emerald rockcod (''Trematomus bernacchii'') enable to be one of the main predators of the medium-sized Antarctic scallops. Otherwise the Antarctic scallop does not itself have many predators and large individuals are adept at jumping and swimming to escape attackers. Any attached juveniles benefit from this. However, the scallops are intolerant of low

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

levels, and mortality sometimes occurs as a result of a pool of relatively fresh water that sometimes forms during the summer months under the sea ice as it melts. There are a large number of epifaunal organisms living on the shells of Antarctic scallops, which may represent 90% of the hard substrate available in a region where rocky surfaces are not common and much of the seabed consists of sediment. Because a diverse community of invertebrates and algae use its shell as a base, the Antarctic scallop is considered to be a "

foundation species In ecology, the foundation species are species that have a strong role in structuring a community. A foundation species can occupy any trophic level in a food web (i.e., they can be primary producers, herbivores or predators). The term was coined ...

"; a species of great importance in its habitat. The fact that the scallops can swim and move to other locations aids in the dispersal of these organisms. The

epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...

s include benthic

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

forams Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class (biology), class of Amoeba, amoeboid protists characterized by streaming granular Ectoplasm (cell biology), ectoplasm ...

, bacteria,

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

ns,

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

s and algae. The foram '' Cibicides refulgens'' lives parasitically on the scallop's shell and also grazes on the algae and bacteria growing there. In a research study, 10 different species of

demosponge Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database). They are sponges with a soft body that covers a har ...

were found growing on a single Antarctic scallop. The demosponge ''

Homaxinella balfourensis ''Homaxinella balfourensis'' is a species of sea sponge in the family (biology), family Suberitidae. It is found in the seas around Antarctica and can grow in two forms, either branching out in one plane like a fan or forming an upright club-like ...

'' was one of the commonest

epibiont An epibiont (from the Ancient Greek meaning "living on top of") is an organism that lives on the surface of another living organism, called the basibiont ("living underneath"). The interaction between the two organisms is called epibiosis. An epi ...

s growing harmlessly on the scallop's shell. The relationship between sponge and scallop may be

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 ...

; the sponge avoids being engulfed in sediment while the scallop benefits from the protection provided by the sponge, which is distasteful to many predators. The hydroid ''

Hydractinia angusta ''Hydractinia'' is a genus of commensal athecate hydroids which belong to the family Hydractiniidae. ''Hydractinia'' species mostly live on hermit-crabbed marine gastropod shells. One species, '' Hydractinia echinata'', is commonly known as sn ...

'' has a mutualistic relationship with the scallop. A study showed that its larvae preferentially settled in the vicinity of other epibionts, usually on scallop shells, and that the scallop larvae were deterred from settling in the vicinity of

colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...

of the hydroid. It is surmised that the hydroid benefits from a solid substrate on which to live, and although the scallop benefits from the protection from predators provided by the stinging cells of the hydroid, it is disadvantaged by the failure of its larvae to establish themselves in their preferred location, on the shells of mature scallops.

Research

A laboratory study examined the effects on the Antarctic scallop of an increase in lead, copper and mercury content in the water. It was found that a rise in levels of heavy metals led to quite severe morphological changes in the scallop and a reduction in

lysosomal A lysosome () is a membrane-bound organelle found in many animal Cell (biology), cells. They are spherical Vesicle (biology and chemistry), vesicles that contain Hydrolysis, hydrolytic enzymes that can break down many kinds of biomolecules. A ly ...

membrane stability. Another experiment involved transplanting scallops from a clean water area to a bay where effluent from an Antarctic base was released. It was found that the scallops were relatively unaffected by the outflows and this resulted in the belief that

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

marine communities were unlikely to be severely affected by such discharges. Another study analysed the tissues of ''Adamussium colbecki'' and compared them with those of ''

Pecten jacobaeus ''Pecten jacobaeus'', the Mediterranean scallop, is a species of scallop, an edible saltwater scallop, a marine bivalve mollusc in the family Pectinidae, the scallops. Description ''Pecten jacobaeus'' usually reaches a length of about , but ...

'', a temperate water species of scallop. It was found that

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...

and

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

were concentrated in the digestive organ of the Antarctic scallop. Cadmium levels in particular were higher in the Antarctic scallop than in ''P. jacobaeus'' and other pectinids, but

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

and

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

, found in the kidney, were considerably lower.

References

{{Taxonbar, from=Q3412060 Pectinidae Molluscs described in 1902 Fauna of Antarctica