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Pecten maximus

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The great scallop, known scientifically as Pecten maximus, is a marine bivalve mollusc. This means it is a saltwater clam with a shell made of two parts. It belongs to the Pectinidae family and is the type species for its genus. These animals are found throughout the northeast Atlantic Ocean. They are highly valued as an edible species in many parts of the world.

Pecten maximus(02)
Pecten maximus(02)

The anatomy of the shell is very distinctive. The right valve, or lower shell, is convex and slightly overlaps the flat left valve. Large specimens can reach a length of 21 cm. The shells feature 12 to 17 wide radiating ribs. These ribs create a crenulated or scalloped edge. Numerous concentric lines also appear on the valves. These lines serve as a growth history for the animal. The shells can show many colors. The left valve is often reddish-brown. The right valve may be white, cream, or pale brown. It can also show pink, red, or bright yellow tints. Some shells even display zigzag patterns or spots.

Inside the shell, the scallop has specialized organs for survival. A very large and powerful adductor muscle allows the animal to open and close its valves. The mantle, which is the soft body tissue, has a unique edge. The outer layer of the mantle features long tentacles. At the base of these tentacles are 30 to 36 simple eyes, also called ocelli. These eyes can be dark blue or green. The scallop also has a finger-like foot. This organ spins byssal threads. These threads are used to attach the animal to the seafloor through a small opening called the byssal notch.

Yeux et tentacules d'une coquille Saint-Jacques (Pecten maximus) (Ifremer 00570-68227 - 49129)
Yeux et tentacules d'une coquille Saint-Jacques (Pecten maximus) (Ifremer 00570-68227 - 49129)

Scallops use several clever mechanisms to live on the ocean floor. They are filter feeders that extract particles from the water. Small hairs called cilia create a feeding current. This current draws water across the gills. The gills trap food particles in a stream of mucous. This mucous then carries the food to the mouth. To hide, the scallop creates a small hollow in the sediment. It does this by opening and closing its valves to eject water from the mantle cavity. This raises the shell at an angle. Water then jets into the sediment to create a recess. Once settled, sand or mud covers the upper valve. Only the tentacles and eyes remain visible to the world.

While they often stay still, scallops can swim to escape predators. Starfish like Asterias rubens and Astropecten irregularis are main predators. When a threat is detected, the scallop performs an escape reaction. It rapidly claps its valves together. This action expels jets of water from each side of the hinge. The scallop jumps forward using the curved edge of the shell. This swimming is usually limited to these sudden bursts of movement. The ability to grow depends on the environment. Scallops in sheltered habitats grow faster than those in high wave action. High waves can make it hard for the feeding apparatus to work. Strong currents can also disturb the delicate process of larval settlement.

Great atlantic scallop, capture production, thousand tonnes, 1950-2022
Great atlantic scallop, capture production, thousand tonnes, 1950-2022

The reproductive biology of Pecten maximus is quite complex. They are hermaphroditic, meaning they have both male and female reproductive organs. These are called gonads and are shaped like tongues. The female gonads are red or orange, while the male gonads are white. Spawning is often influenced by temperature and age. Mature scallops generally spawn from April or September. A three-year-old scallop can release 15 to 21 million oocytes per emission. Fertilization happens externally in the water column. The larvae can drift for up to a month. This long larval stage helps the species distribute itself across wide areas.

Humans have a significant relationship with this species through fisheries and aquaculture. In 1999, the United Nations reported a total catch of 35,411 tonnes. The United Kingdom and France were the largest producers that year. In the UK, scallop fishing is one of the top five fisheries by value. Some scallops are caught using Newhaven scallop dredges. Others are gathered by hand by divers. Aquaculture, or farming, is also practiced in countries like Norway and France. However, scientists monitor scallops closely for domoic acid. This is a toxin that can cause Amnesic Shellfish Poisoning in humans.

Pecten maximus(02)
Pecten maximus(02)
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File:Pecten maximus(02).jpg
Pecten maximus(02).jpg
File:Yeux et tentacules d'une coquille Saint-Jacques (Pecten maximus) (Ifremer 00570-68227 - 49129).jpg
Yeux et tentacules d'une coquille...
File:Great atlantic scallop, capture production, thousand tonnes, 1950-2022.svg
Great atlantic scallop, capture...
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