Bivalve Molluscs Biology Ecology And Culture Elizabeth Gosling PdfBy Maclovio C. In and pdf 09.05.2021 at 23:20 4 min read
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The giant clams are the members of the clam genus Tridacna that are the largest living bivalve mollusks. Tridacna gigas is one of the most endangered clam species.
Wood's Hole Oceanographic Institution A prominent research facility for marine animals.
Marine Bivalve Molluscs is a comprehensive and thoroughly updated second edition of Bivalve Molluscs, covering all major aspects of this important class of invertebrates. As well as being an important class biologically and ecologically, many of the bivalves are fished and cultured commercially e. Elizabeth Gosling has written a landmark book that will stand for many years as the standard work on the subject. Chapters in Marine Bivalve Molluscs cover morphology, ecology, feeding, reproduction, settlement and recruitment, growth, physiology, fisheries, aquaculture, genetics, diseases and parasites, and public health issues. A full understanding of many of these aspects is vital for all those working in bivalve fisheries and culture.
Marine Bivalve Molluscs (eBook)
However, the common name "scallop" is also sometimes applied to species in other closely related families within the superfamily Pectinoidea , which also includes the thorny oysters. Scallops are a cosmopolitan family of bivalves which are found in all of the world's oceans, although never in fresh water. They are one of very few groups of bivalves to be primarily "free-living", with many species capable of rapidly swimming short distances and even of migrating some distance across the ocean floor.
A small minority of scallop species live cemented to rocky substrates as adults, while others attach themselves to stationary or rooted objects such as sea grass at some point in their lives by means of a filament they secrete called a byssal thread.
The majority of species, however, live recumbent on sandy substrates, and when they sense the presence of a predator such as a starfish , they may attempt to escape by swimming swiftly but erratically through the water using jet propulsion created by repeatedly clapping their shells together. Scallops have a well-developed nervous system, and unlike most other bivalves all scallops have a ring of numerous simple eyes situated around the edge of their mantles.
Many species of scallops are highly prized as a food source, and some are farmed as aquaculture. The word "scallop" is also applied to the meat of these bivalves, the adductor muscle , that is sold as seafood. The brightly coloured, symmetric, fan-shaped shells of scallops with their radiating and often fluted ornamentation are valued by shell collectors, and have been used since ancient times as motifs in art, architecture, and design. Owing to their widespread distribution, scallop shells are a common sight on beaches and are often brightly coloured, making them a popular object to collect among beachcombers and vacationers.
Scallops inhabit all the oceans of the world, with the largest number of species living in the Indo-Pacific region. Most species live in relatively shallow waters from the low tide line to m, while others prefer much deeper water. Although some species only live in very narrow environments, most are opportunistic and can live under a wide variety of conditions.
Scallops can be found living within, upon, or under either rocks, coral, rubble, sea grass , kelp , sand, or mud. Most scallops begin their lives as byssally attached juveniles, an ability that some retain throughout their lives while others grow into freeliving adults. Very little variation occurs in the internal arrangement of organs and systems within the scallop family, and what follows can be taken to apply to the anatomy of any given scallop species.
The shell of a scallop consists of two sides or valves , a left valve and a right one, divided by a plane of symmetry. The model scallop shell consists of two similarly shaped valves with a straight hinge line along the top, devoid of teeth, and producing a pair of flat wings or "ears" sometimes called "auricles", though this is also the term for two chambers in its heart on either side of its midpoint, a feature which is unique to and apparent in all adult scallops.
These growth rings increase in size downwards until they reach the curved ventral edge of the shell. The shells of most scallops are streamlined to facilitate ease of movement during swimming at some point in their lifecycles, while also providing protection from predators. Scallops with ridged valves have the advantage of the architectural strength provided by these ridges called "ribs", although the ribs are somewhat costly in terms of weight and mass.
A unique feature of the scallop family is the presence, at some point during the animal's lifecycle, of a distinctive and taxonomically important shell feature, a comb-like structure called a ctenolium located on the anterior edge of the right valve next to the valve's byssal notch.
Though many scallops lose this feature as they become free-swimming adults, all scallops have a ctenolium at some point during their lives, and no other bivalve has an analogous shell feature. The ctenolium is found in modern scallops only; both putative ancestors of modern scallops, the entoliids and the Aviculopectinidae, did not possess it.
Like the true oysters family Ostreidae , scallops have a single central adductor muscle, thus the inside of their shells has a characteristic central scar, marking the point of attachment for this muscle.
The adductor muscle of scallops is larger and more developed than those of oysters , because scallops are active swimmers; some species of scallops are known to move en masse from one area to another. In scallops, the shell shape tends to be highly regular, and is commonly used as an archetypal form of a seashell.
These eyes represent a particular innovation among molluscs, relying on a concave, parabolic mirror of guanine crystals to focus and retro-reflect light instead of a lens as found in many other eye types. Additionally, some scallops alter their swimming or feeding behavior based on the turbidity or clarity of the water, by detecting the movement of particulate matter in the water column. Scallops are filter feeders , and eat plankton. Unlike many other bivalves, they lack siphons.
Water moves over a filtering structure, where food particles become trapped in mucus. Next, the cilia on the structure move the food toward the mouth. Then, the food is digested in the digestive gland, an organ sometimes misleadingly referred to as the "liver", but which envelops part of the oesophagus, intestine, and the entire stomach.
Waste is passed on through the intestine the terminus of which, like that of many mollusks, enters and leaves the animal's heart and exits via the anus. Like all bivalves, scallops lack actual brains. Instead, their nervous system is controlled by three paired ganglia located at various points throughout their anatomy, the cerebral or cerebropleural ganglia, the pedal ganglia, and the visceral or parietovisceral ganglia.
All are yellowish. The visceral ganglia are by far the largest and most extensive of the three, and occur as an almost-fused mass near the center of the animal — proportionally, these are the largest and most intricate sets of ganglia of any modern bivalve. From these radiate all of the nerves which connect the visceral ganglia to the circumpallial nerve ring which loops around the mantle and connects to all of the scallop's tentacles and eyes.
This nerve ring is so well developed that in some species, it may be legitimately considered an additional ganglion. The cerebral ganglia are the next-largest set of ganglia, and lie distinct from each other a significant distance dorsal to the visceral ganglia. They are attached to the visceral ganglia by long cerebral-visceral connectives, and to each other via a cerebral commissure that extends in an arch dorsally around the esophagus. The cerebral ganglia control the scallop's mouth via the palp nerves, and also connect to statocysts which help the animal sense its position in the surrounding environment.
They are connected to the pedal ganglia by short cerebral-pedal connectives. The pedal ganglia, though not fused, are situated very close to each other near the midline. From the pedal ganglia, the scallop puts out pedal nerves which control movement of, and sensation in, its small muscular foot. The scallop family is unusual in that some members of the family are dioecious males and females are separate , while other are simultaneous hermaphrodites both sexes in the same individual , and a few are protoandrous hermaphrodites males when young then switching to female.
Red roe is that of a female, and white, that of a male. Spermatozoa and ova are released freely into the water during mating season, and fertilized ova sink to the bottom. After several weeks, the immature scallops hatch and the larvae, miniature transparent versions of the adults called "spat", drift in the plankton until settling to the bottom again an event called spatfall to grow, usually attaching by means of byssal threads.
Some scallops, such as the Atlantic bay scallop Argopecten irradians , are short-lived, while others can live 20 years or more. Age can often be inferred from annuli , the concentric rings of their shells. Scallops are mostly free-living and active, unlike the vast majority of bivalves, which are mostly slow-moving and infaunal.
All scallops are thought to start out with a byssus , which attaches them to some form of substrate such as eelgrass when they are very young.
Most species lose the byssus as they grow larger. A very few species go on to cement themselves to a hard substrate e. Chlamys distorta and Hinnites multirigosus. However, the majority of scallops are free-living and can swim with brief bursts of speed to escape predators mostly starfish by rapidly opening and closing their valves.
They often do this in spurts of several seconds before closing the shell entirely and sinking back to the bottom of their environment. A jumping scallop usually lands on the sea floor between each contraction of its valves, whereas a swimming scallop stays in the water column for most or all of its contractions and travels a much greater distance though seldom at a height of more than 1 m off the sea bed and seldom for a distance of greater than 5 m.
Should a swimming scallop land on its left side, it is capable of flipping itself over to its right side via a similar shell-clapping movement called the righting reflex. So-called singing scallops are rumored to make an audible, soft popping sound as they flap their shells underwater though whether or not this happens is open to some debate.
Most species of the scallop family are free-living, active swimmers, propelling themselves through the water through the use of the adductor muscles to open and close their shells.
Swimming occurs by the clapping of valves for water intake. Closing the valves propels water with strong force near the hinge via the velum, a curtain-like fold of the mantle that directs water expulsion around the hinge. Scallops swim in the direction of the valve opening, unless the velum directs an abrupt change in course direction. Other species of scallops can be found on the ocean floor attached to objects by byssal threads.
Byssal threads are strong, silky fibers extending from the muscular foot, used to attach to a firm support, such as a rock. Some can also be found on the ocean floor, moving with the use of an extendable foot located between their valves or burrowing themselves in the sand by extending and retracting their feet.
They serve as a vital defense mechanism for avoiding predators. Though rather weak, their series of eyes can detect surrounding movement and alert precaution in the presence of predators, most commonly sea stars, crabs, and snails. Older individuals show lower mitochondrial volume density and aerobic capacity, as well as decreased anaerobic capacity construed from the amount of glycogen stored in muscle tissue.
Seasonal changes in temperature and food availability have been shown to affect muscle metabolic capabilities. The properties of mitochondria from the phasic adductor muscle of Euvola ziczac varied significantly during their annual reproductive cycle. Summer scallops in May have lower maximal oxidative capacities and substrate oxidation than any other times in the year. This phenomenon is due to lower protein levels in adductor muscles. Scallops do occasionally produce pearls , though scallop pearls do not have the buildup of translucent layers or "nacre" which give desirability to the pearls of the feather oysters , and usually lack both lustre and iridescence.
They can be dull, small, and of varying colour, but exceptions occur that are appreciated for their aesthetic qualities. Some scallops, including Chlamys hastata , frequently carry epibionts such as sponges and barnacles on their shells.
The relationship of the sponge to the scallop is characterized as a form of mutualism, because the sponge provides protection by interfering with adhesion of predatory sea-star tube feet,    camouflages Chlamys hastata from predators,  or forms a physical barrier around byssal openings to prevent sea stars from inserting their digestive membranes.
Thus, barnacle larvae settlement occurs more frequently on sponge-free shells than sponge-encrusted shells. In fact, barnacle encrustation negatively influences swimming in C. Those swimming with barnacle encrustation require more energy and show a detectable difference in anaerobic energy expenditure than those without encrustation.
In the absence of barnacle encrustation, individual scallops swim significantly longer, travel further, and attain greater elevation. Many scallops are hermaphrodites having female and male organs simultaneously , altering their sex throughout their lives, while others exist as dioecious species, having a definite sex. In this case, males are distinguished by roe-containing white testes and females with roe-containing orange ovaries.
At the age of two, they usually become sexually active, but do not contribute significantly to egg production until the age of four. The process of reproduction takes place externally through spawning, in which eggs and sperm are released into the water.
Spawning typically occurs in late summer and early autumn; spring spawning may also take place in the Mid-Atlantic Bight. Once an egg is fertilized, it is then planktonic, which is a collection of microorganisms that drift abundantly in fresh or salt water. Larvae stay in the water column for the next four to seven weeks before dissipating to the ocean floor, where they attach themselves to objects through byssus threads.
Byssus is eventually lost with adulthood, transitioning almost all scallop species into free swimmers. The family name Pectinidae, which is based on the name of the type genus, Pecten , comes from the Latin pecten meaning comb , in reference to a comb-like structure of the shell which is situated next to the byssal notch.
The fossil history of scallops is rich in species and specimens. The earliest known records of true scallops those with a ctenolium can be found from the Triassic period , over million years ago. The survivors speciated rapidly during the Tertiary period. Nearly 7, species and subspecies names have been introduced for both fossil and recent Pectinidae.
Palliolinae in part.
Marine Bivalve Molluscs (eBook)
Elizabeth Gosling PhD, DSc, based at the Galway-Mayo Institute of Technology, Ireland, is an author of international repute with a huge wealth of research, teaching and hands-on experience of working with bivalves. Details zum Adobe-DRM. Mit dem amazon-Kindle ist es aber nicht kompatibel. Buying eBooks from abroad For tax law reasons we can sell eBooks just within Germany and Switzerland. Regrettably we cannot fulfill eBook-orders from other countries.
Bivalve Molluscs: Biology, Ecology and Culture. Editor(s). Elizabeth Gosling. First published January Print ISBN |Online.
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However, the common name "scallop" is also sometimes applied to species in other closely related families within the superfamily Pectinoidea , which also includes the thorny oysters. Scallops are a cosmopolitan family of bivalves which are found in all of the world's oceans, although never in fresh water. They are one of very few groups of bivalves to be primarily "free-living", with many species capable of rapidly swimming short distances and even of migrating some distance across the ocean floor. A small minority of scallop species live cemented to rocky substrates as adults, while others attach themselves to stationary or rooted objects such as sea grass at some point in their lives by means of a filament they secrete called a byssal thread. The majority of species, however, live recumbent on sandy substrates, and when they sense the presence of a predator such as a starfish , they may attempt to escape by swimming swiftly but erratically through the water using jet propulsion created by repeatedly clapping their shells together.
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