The exhibition "Shells on Stamps" is currently on display at the Beijing Museum of Natural History from July 7 to October 7. The exhibition shows the extremely close relationship between shellfish and humans. They are rich in species and widely distributed, and they can be found everywhere in the sea, in rivers, on hillsides, and in the shade of trees. They have been one of the most commonly used ingredients since ancient times, and according to rough statistics, there are at least 400 kinds of shellfish on tables around the world. At the same time, the atmosphere of shell collection and stamp collection is so great, the crowd is large, and the scope is wide, which can be called the two major popular in the collection industry. Today, we continue to revisit the second part of Mr. Yang Siyi's article "Shells and Shell Makers" published in the 1989 02 issue of Nature magazine, following the names of shells to understand the classification of shellfish.
Maker of shells and shells
Taxonomy of shells
Yang Siyi
People collect shells, either because they like their magnificence or by the strangeness of their shape. As for what exactly is a shell? How did they come about? Probably very few people have asked. Some people may know that they are the shells of a class of animals, but they are often blind to such animals and their lives. This situation seems somewhat perverse. Because the owners of the shells are the same inhabitants of the earth as us, they are our "neighbors", and their survival is closely related to our human life. It is necessary for us to understand them.
In order to know the maker of the shell, you may wish to observe the "snail" that everyone is most familiar with. Whenever it rains in spring and summer, they can be seen everywhere in corners, under trees, vegetable fields, and meadows. As they crawl, two pairs of antennae can be seen at the front, and the ventral surface of the antennae is its mouth. Needless to say, this front is the head of the snail. There is a large foot behind the head, suitable for crawling. The back of the foot carries a shell. Remove the shell to see a film wrapped around the snail's body like a coat. People call this film the mantle film. Cut open the mantle membrane to see the various internal organs of the snail. The body of all shellfish is made up of the head, feet, mantle membrane and internal organs. The shell is only the secretion of the mantle membrane. Because this type of animal is soft and boneless, it is collectively called mollusk.
As early as the Cambrian era half a billion years ago, molluscs appeared on Earth. They can be seen in rivers, lakes and seas, alpine plains, and even arid deserts. Although the bodies of mollusks are composed of heads, feet, mantle membranes and internal organs, different taxa have diverged greatly over the long course of evolution. According to their different body structure, they can be divided into seven major groups.
No board class
These animals resemble worms, have no shells on their bodies, but have stratum corneum and various calcareous bone needles on their coat membranes. There are about 100 species in the world, all of which live in the sea, and the dragon girl hairpin found along the coast of China belongs to this type of animal.
Multi-board class
Their bodies are generally oval in shape, covered with eight plate-like shells on the back, and the mantle membrane only covers the back of the body. Most of them live in the intertidal zone or shallow sea, but a few live in the deep sea. There are about 600 species in the world, and the common stone turtle on the rock shore belongs to this category.
Veneer class
This is a very old mollusk with an oval-shaped body and a shell like a hat. They live a creepy life in the deep sea. In the past, such animals were only fossilized, and it was not until 1952 that live animals were discovered, and people named them New Saucer Shells. Only 8 species have been found in the world so far in 1970. There are many special places in their body structure, which are relatively close to the appearance of their ancestors. The discovery of such "living fossils" provides useful new materials for exploring the origin and evolution of molluscs.
Flap gills
The left and right sides of the body of such animals are flattened, and from the back to the ventral surface, they are "wrapped" by a mantle membrane on the left and right and a scallop on the left and right produced by the mantle membrane. They are mostly buried in sediment and live on tiny organic matter filtered through the water by lobed gills. The head has been completely degraded due to its long-term use in shells, and the feet are flattened, like an axe, which is very convenient for digging sediment. There are about 15,000 species worldwide, most of which live in the oceans and a few in freshwater. They are the main objects of fishing and farming, such as mussels, oysters, scallops, river mussels and so on.
Foot diggers
This is a class of marine benthic molluscs. They look like horns or ivory with openings at both ends. The large mouth end is the head end, and the small mouth end is the tail end. The foot is developed, columnar, and can protrude from the head end to dig up sediment, so it is called foot diggers. Because they have lived buried on the seafloor for a long time, their heads have also degenerated. There are not many types of such animals, there are about 200 species in the world, and the common ones in China are large-horned shellfish, long-horned shellfish, octagonal shellfish and so on.
Gastropods
This is the largest group of molluscs, and their feet are located on the ventral surface of the body, so they are called gastropods, and they usually have a spiral shell, so some people call them snails. So far, more than 80,000 kinds of species have been found in the world, distributed all over the world, as deep as 8,000 meters deep sea, as high as more than 6,000 meters high mountains, can be found in their traces. Their lifestyles are diverse and their morphology is extremely varied, and most of the shells we collect belong to this type of animal.
Cephalopods
Including our common squid, octopus, squid and so on. Their heads and feet are very developed, and because the foot rings are born in front of the head, they are called cephalopods. All of these animals live in the ocean, living a swimming life, and their shells are mostly degraded or enclosed in the mantle membrane. There are many kinds of fossil animals, but only more than 500 species survive today.
The exhibition of "Shells on Stamps" ends on October 7
Welcome to the Exhibition during the National Day holiday
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