Where do pearls come from?
Pearls are highly valued as gemstones. Most gemstones come from the Earth, but pearls come from living things. They are created by mollusks, such as oysters.
Importance of Mollusks
Mollusks are important in a variety of ways; they are used as food, for decoration, in jewelry, and in scientific studies. They are even used as roadbed material and in vitamin supplements.
Mollusks as Food
Edible species of mollusks include numerous species of clams, mussels, oysters, scallops, marine and land snails, squid, and octopuses. Many species of mollusks, such as oysters , are farmed in order to produce more than could be found in the wild ( Figure below ).
An oyster harvest in France.
Today, fisheries in Europe, Japan, and the US alone produce over 1 billion pounds of oyster meat each year. Abalone (a marine gastropod mollusk), a great delicacy, can fetch up to three hundred dollars per pound. Eating mollusks is associated with a risk of food poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations to reduce this risk. At certain times of the year, (usually the warmer months) many species of saltwater mollusks become very poisonous due to an algal bloom known as "red tide." The mollusks filter feed on the tiny creatures (called "dinoflagellates" in the bloom) that produce the toxins. Eating shellfish during a red tide can cause serious illness and even death to humans.
Tastes in molluscan food vary tremendously from one person to the next and from culture to culture; however, when it comes to a question of survival, most mollusks are edible. Some are considered delicacies such as oysters and escargot while others such as the clams and mussels of freshwater ponds and streams are less likely to be consumed due to taste, but none-the-less are very edible. Land-based mollusks are also eaten. France alone consumes 5 million pounds of escargot (a snail that lives in trees) every year. Of course, some people are allergic to mollusks and need to be careful about consuming any kind of shelled animals.
Mollusks in Decoration and Jewelry
Two natural products of mollusks used for decorations and jewelry are pearls and nacre. A pearl is the hard, round object produced within the mantle of a living shelled mollusk. Pearls are produced by many bivalves when a tiny particle of sand or grit is trapped between the mantle and the shell. It's as if the mollusk has a splinter. The mollusk forms a protective covering around the irritant. Most pearls used as jewelry are made by pearl oysters and freshwater mussels; most of the ones sold are cultured and not wild. Natural pearls have been highly valued as gemstones and objects of beauty for many centuries. The most desirable pearls are produced by oysters and river mussels. The substance used to form the pearl covering, is made from the mother of pearl material that lines the interior of the shell.
Mother of pearl is also known as nacre. Nacre is the iridescent inner shell layer. It can be found in buttons, watch faces, knives, guns, and jewelry. It is also used to decorate various musical instruments.
Mollusks in Scientific Studies
Several mollusks are ideal subjects for scientific investigation of the nervous system. The giant squid has a sophisticated nervous system and a complex brain for study. The California sea slug, also called the California sea hare, is used in studies of learning and memory because it has a simple nervous system, consisting of just a few thousand large, easily identified neurons. These neurons are responsible for a variety of learning tasks. Some slug brain studies have even allowed scientists to better understand human brains. Some octopuses and squid are incredibly smart. They are capable of learning to solve problems and do mazes.
- Some mollusks, such as oysters and scallops, are important food sources.
- Mollusks are used for decoration and are important in scientific studies.
Use the resources below to answer the questions that follow.
Explore More I
- The Squids Giant Axons at http://www.youtube.com/watch?v=omXS1bjYLMI (4:49)
- What large tubular structures did Professor Young find in squids?
- Why were the size of these structures important to Professor Young's work?
- What did scientists discover when they were able to empty the contents of a squid axon?
- How did World War II help the study of neuron functioning?
Explore More II
- How are pearls made? at http://www.whyzz.com/how-are-pearls-made
- How are natural pearls made?
- How are cultured pearls made?
- Name three mollusks that are used for food.
- What is a pearl?
- What mollusks produce pearls? How are they made?
- What makes the California sea slug ideal for studies of learning and memory?