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Placopecten magellanicus

By Kathryn Hodges

Geographic Range

Placopecten magellanicus, Deep Sea Scallops, are native to the Atlanic Ocean and range from Labrador to North Carolina. Labrador is located very near New Foundland on the Eastern coast of Canada. They have now become more dispersed throughout this area as a result of farmers introducing them to varying locations in order to breed them for culinary purposes, but the majority remain in the Northern Atlantic Ocean. (Borradaile and Potts, 1963)

Habitat

Placopecten magellanicus live in moderately deep water. Populations north of Cape Cod live in shallow water, approximately twenty meters. South of Cape Cod, populations live in deeper water ranging from forty to two-hundred meters. They can only survive in marine environments and prefer the cool water of the Northern Atlantic, which stays around sixty-eight degrees Fahrenheit. While resting, they lie on the sand or mud of the ocean bottom. (Hart, January 2001; Morris, 1951)

  • Range depth
    20 to 200 m
    65.62 to 656.17 ft
  • Average depth
    40 m
    131.23 ft

Physical Description

Deep sea scallops secrete two vavles, which are large, thick, and oval-shaped. This shell is often greater in height than width. The valves are unequal in size, with the lower being almost flat and the upper being convex. Grooves radiate from the hinge towards the shell edge. The upper valve is dark in color, usually red or pinkish brown and sometimes rayed with white, while the lower is lighter and is pinkish white. The shell's inside is a glossy white with a distinctive muscular scar where the soft body attaches. The muscle itself is white or tan in color and has two labial or feeding palps with a mouth in between. The scallop's body is wedge-shaped with a ventrally located foot. The gills or ctenidia are in the mantle cavity and are commonly enlarged and have a complex arrangement. A row of eyes peaks from in between the the valves and are attached to the mantle cavity. (Borradaile and Potts, 1963; Hart, January 2001; Morris, 1951; Pennak, 1989)

  • Range length
    10 to 23 cm
    3.94 to 9.06 in
  • Average length
    15 cm
    5.91 in

Development

After fertilization, P. magellanicus develop into a ciliated larva known as the trochosphere. At this stage, they have cilia near their tops and also have a cilia ring around their middle. Then, the larvae quickly mature to veligers. These planktotrophic larvae are ciliary feeders and float in plankton fields for approximately two or three months. The larvae continue to develop and begin to secrete two valves from their mantle cavity as they reach adulthood. During the first several years of life, scallops rapidly increase in size and bulk. The third to fifth year has the most growth. They increase shell height by fifty to eighty percent and quadruple in body weight. Once adult scallops, they become free swimming. (Borradaile and Potts, 1963; Hart, January 2001; Morris, 1951)

Reproduction

Instead of releasing eggs and sperm randomly, scallops stimulate one another to spawn at the same time. The sperm is released first and then enters the food current of other scallops, which causes them to release eggs into the mantle cavity. (Pearse, et al., 1987)

By the age of two, P. magellanicus are sexually mature, but do not actively produce eggs until four. The majority of deep sea scallops undergo multiple sex changes during their lifetime. They are known as functionally ambisexual and shelter the ova and sperm in the same gonad, but the two are produced in different areas of the gonad. About four percent are hermaphrodites and carry both an ovary and testis within the mantle cavity. The ovary is a very bright pink when carrying ripe eggs and the cream colored testis lie behind the ovary. The two are fused together and have short ducts with no glands. Eggs are not released in the water, but wait for the sperm in the mantle cavity. Fertilization occurs when the sperm usually meet the eggs near the opening of the mantle cavity. Then, the scallops immediately release the zygotes into the water. (Borradaile and Potts, 1963; Hart, January 2001; Morton, 1979; Pearse, et al., 1987)

  • Breeding season
    Late Summer and early Fall, but can also occur in Spring within populations living in the Mid-Atlantic region
  • Range age at sexual or reproductive maturity (female)
    2 (low) years
  • Range age at sexual or reproductive maturity (male)
    Two (low) years

Because Deep Sea Scallops create so many sperm and eggs to ensure numerous offspring, they do not have the energy to take care of the offspring. Also, external fertilization does not allow the parents to keep track of their offspring. They produce too many offspring to differentiate between their own and the hundreds of other offspring in the area. (Pearse, et al., 1987)

  • Parental Investment
  • pre-fertilization
    • provisioning

Lifespan/Longevity

Deep sea scallops reach full adulthood at four years of age and tend to live several years afterward. On average, they live for approximately six to eight years. (Borradaile and Potts, 1963; Hart, January 2001)

  • Typical lifespan
    Status: wild
    6 to 8 years

Behavior

P. magellanicus is a solitary animal, but can be found in groups of other scallops although this grouping is not intentional. Though scallops do need to be in close proximity for the male to stimulate the female for reproduction. The larva can be sessile, but the adult scallop is mobile and when it is not moving, it is resting on the ocean floor. (Borradaile and Potts, 1963)

Communication and Perception

Deep sea scallops respond to sight and touch. The scallops' eyes are very developed with corneas and lenses, which serves as their dominant means of interaction. The only time they communicate with other scallops is during reproduction. The sperm stimulate the release of eggs. (Borradaile and Potts, 1963)

Food Habits

The deep sea scallop's ctenidia and labial cilia serve as instruments for food collection. There is a ventral and dorsal siphon. Water enters the ventral siphon and a current is maintained to pass through the gill lamellae. Here, the scallop separates food particles from mud and sand according to size. The ctnedia then transport the food particles to the mantle cavity and circulate over many groups of cilia. The particles become covered with mucus and are pushed either toward the mouth or the rejection path, which leaves through the dorsal siphon. The mucus covered food is then carried to the stomach through the esophagus, but first passes through the crystalline style, a gelantinous rotating rod. Here, the food is digested in intracellular food vacoules and waste is removed through the intestines and out through the anus.

Foods eaten include microscopic plants, bacteria and organic particles. (Borradaile and Potts, 1963; Pearse, et al., 1987)

Predation

Even though deep sea scallops have a high concentration of sensory organs near the edge of the mantle cavity, they only have a relatively simple nervous system. Visceral ganglia near the optic lobes fuse with other ganglia to form a simplistic "visceral brain", which constitutes most of the scallop's nervous system. The concentration of sensory organs allow the scallop to be aware of its surroundings at all times. Most prominent and useful are their row of eyes between the two vavles, which aid in watching for predators. The eyes are usually coblat blue in color and are located on the tip of pallial tentacles. Although their eyes are complete with cornea and lens, they are unable to discern shapes. They can only detect changes in light and movement and react to flashing lights or stripes that move at particular speeds, which resemble speeds of their predators, starfish and whelks. The chemical sensitive pallial tentacles are also able to react to excretions of starfish. When a predator is spotted or the scallop is touched, the scallop quickly propels itself from danger. They can do this by rapidly clapping their two valves together and moving in jerks or darts. Movement occurs through a type of jet propulsion. A jet of water is forced backwards and out through the wings and hinge. The locomotion is mainly powered by the large muscle known as the body or mantle cavity. (Borradaile and Potts, 1963; Pearse, et al., 1987)

Ecosystem Roles

P. magellanicus play a critical role in their ecosystems. While feeding, they recycle incredible amounts of organic material and filter harmful bacteria from the water. They also aid in purifying polluted water. (Pearse, et al., 1987)

Economic Importance for Humans: Positive

Deep sea scallops are predominantly used in cuisine. The scallop's valves are removed and the soft adductor muscles are consumed in many dishes around the world. The shells hold an artistic appeal and are bought by thousands of tourists visiting the Northern Coast. Indians continue to use the convex shells as plates. (Borradaile and Potts, 1963)

  • Positive Impacts
  • food

Contributors

Renee Sherman Mulcrone (editor).

Kathryn Hodges (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

crepuscular

active at dawn and dusk

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

photic/bioluminescent

generates and uses light to communicate

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

planktivore

an animal that mainly eats plankton

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sessile

non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

References

Borradaile, L., Potts. 1963. The Invertebrata: A Manual for the Use of Students. Cambridge: The University Press.

Hart, D. January 2001. "Status of Fisheries Resources off Northeastern United States" (On-line). Accessed 11/04/04 at http://www.wh.whoi.edu/sos/spsyn/iv/scallop/.

Morris, P. 1951. Field guide to the shells of our Atlantic coast. Boston: Houghton Mifflin.

Morton, J. 1979. Molluscs. London: Hutchinson & Co. Ltd..

Pearse, V., J. Pearse, M. Buchsbaum, R. Buchsbaum. 1987. Living Invertebrata. California: The Bookwood Press.

Pennak, R. 1989. Fresh Water Invertabrates of the United States: Protozoa to Mollusca. New York: John Wiley & Sons, Inc..

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