Characteristics of mollusks? What are the main characteristics of mollusks?

The body is soft and unsegmented, and is usually divided into cephalic-foot (some heads are vestigial or absent; foot muscular) and visceral-mantle (composed of dorsal visceral mass, mantle, and mantle cavity). The dorsal ** fold extends downward into the mantle, which secretes a calcareous shell encapsulated in vitro (some degenerate into an inner shell or no shell). No true endoskeleton.

There is a blood cavity (i.e., a series of dilated venous sinuses) in the body. Blood chambers function like fluid bones to maintain tension in the body. The blood contains a small number of astrologic or amoeba-shaped cells.

Blood contains hemocyanins (gastropods and cephalopods). The muscles of the mouth contain myoglobin. True body cavities degenerate into genital and pericardiac cavities.

The body surface usually has cilia or mucus. There is a toothed tongue in the mouth. The toothed tongue is a unique organ of most mollusks, consisting of multiple rows of toothed plates, shaped like a file, and used to aid in feeding.

Large digestive glands are common. Ctenophores have gills with cilia on the surface that stimulate water flow (in bivalves it helps to filter food particles from water). The excretory organ is the kidney.

Marine species excrete ammonia or urea, and terrestrial gastropods excrete uric acid. Hermaphroditic or allogeneic. In vitro fertilization for cephalopods and parts of gastropods, and allogeneic fertilization for hermaphrodites.

There are several pairs of ganglia. The largest mollusk, the king squid, has a wrist of 12 meters (40 feet), and the smallest is a snail that is only 1 centimeter long. Molluscas are found in a variety of habitats such as seawater, freshwater, terrestrial (especially woodlands, and even dry areas).

Some gastropods are endoparasites of other animals, and mollusks are economically important. Many aquatic species, especially clams, oysters, scallops and mussels, are edible and can be harvested or farmed. The terrestrial genus Helix is used as a delicacy in Europe.

Many shells or pearls can be used as decorations, and ship maggots and the like can harm docks and wooden boats. Some freshwater snails are intermediate hosts for parasitic worms.

The morphological structure of mollusks varies greatly, but the basic structure is the same. The body is soft and has a hard shell in which the body is hidden for protection, and they are quite slow to move due to the fact that the hard shell hinders movement. It is not segmented, it can be divided into three parts: head, foot, and visceral mass, and the outer membrane often secretes shells.

The foot is shaped like an axe and has two shells, like an oyster.

Petal gill (river mussel): bivalves, valve gills, axe-footed, headless.

Gastropoda (snails): monococ, spiral-shaped; The head is symmetrical from side to side, and the internal organs are asymmetrical; The pairs degenerate on one side, leaving only one; The head is distinct, and the feet are located on the ventral surface.

Cephalopoda (squid): symmetrical left and right; The head is well developed, and the feet are located on the head; degeneration or disappearance of shells, inner shells; Highly developed nerves and senses.

The body is soft, not segmented (veneers can be segmented), and can be divided into four parts: head, feet, visceral mass and mantle (mantle) formed by the expansion of the back**. Molluscas are dioecious, with a few hermaphrodites.

Molluscas are three-germ, symmetrical on both sides, and have a true body cavity. The true body cavity of mollusks is formed by the fissure cavity method, that is, the body cavity formed by the mesoderm. However, the true body cavity of mollusks is underdeveloped and only exists in the pericardiac cavity and gonadal cavity, so the significance of the appearance of the true body cavity will be left to the Annelida.

Molluscs vary greatly in morphology, but they can be divided into four parts in terms of structure: head, foot, visceral sac and mantle. The head is located at the front end of the body, the foot is located at the back of the head, the ventral surface of the body, is a multi-muscular motor organ that extends from the body wall, the visceral sac is located on the back of the body, and is an internal organ surrounded by the soft body wall, the mantle is a membrane or a pair of membranes formed by the extension and drooping of the body wall on the back of the body, and the cavity between the mantle and the visceral sac is the mantle cavity. Calcium carbonate is secreted from the mantle to the body surface, forming one or two shells that surround the entire body, and a few species of shells are surrounded by the body wall or the shells disappear completely.

These basic structures vary greatly from class to class.

Molluscs have an intact digestive tract, respiratory and circulatory systems, and metanephridium, which is more evolved than the protokidney.

There are many species of mollusks and they are widely distributed. There are more than 110,000 species and 35,000 fossil species, making it the second largest group in the animal kingdom after arthropods. In particular, some mollusks use their "lungs" to breathe, and their bodies have the ability to regulate water, making mollusks and arthropods the only terrestrial animals suitable for living on the ground.

The main characteristics of mollusks:

1. The body is divided into three parts: head, feet, and internal organs.

2. It has a shell and a mantle.

3. The true body cavity is extremely degenerate.

4. The appearance of full-time respiratory organs, gills.

5. Except cephalopods.

Except for lung snails and cephalopods, most of the other marine animals are indirectly developed.

6. The system is symmetrical on both sides, the body is not segmented, it has a mantle membrane and a shell, and the body cavity is a true body cavity, but it is not developed.

7. Most species are dioecious or even heteromorphic, and a few species are hermaphroditic.

Available Value. 1. Edible value.

Seafood abalone, jade snails, fragrant snails, red snails, Dongfeng snails, mud snails.

Cockles, mussels. Scallops, glams, oysters, clams.

Clams, clams, razor clams, squid, squid, octopus, freshwater snails, snails, mussels, clams, and land-dwelling snails are delicious and have high nutritional value.

2. Agricultural value.

Small mollusks with a high yield can be used as fertilizer or fodder for farmland, river clams.

Freshwater fish can be raised. The shells of mollusks are a good raw material for burnt lime. Shells with thick nacre (such as mussels, horseshoe snails, etc.) are the raw materials for making buttons.

3. Craft or decoration.

The shells of many shellfish have unique shapes and patterns, which are shiny and colorful, and are the favorite items of ancient and modern Chinese and foreign people.

The characteristics are as follows:The main characteristics of mollusks: soft body, mantle on the surface, mostly with shells; The locomotor organ is the foot.

Molluscs (Latin scientific name: granulifusus kiranus), also known as shellfish, is a general term for mollusks, and is the largest group except arthropods, with about 100,000 species, and the system varies greatly.

Introduction:

Characteristic, a Chinese word, pronounced tè zhēng, means the characteristic of a thing that is different from others.

The Biography of Lang Yi in the Book of the Later Han Dynasty: "The birth of heaven is solid, and it must be a holy Han, and it is advisable to sign it in order to show the Quartet." ”

Northern Qi Yan Zhitui "Yan's Family Motto: Later Marry": "In Jianguang, the bus is characteristic, and it is in the service." ”

Jin Yuanhao asked "Wang Huanghua's Tombstone": "Avoid the rebellion at the end of the Han Dynasty and migrate to Liaodong." Cao Gong's characteristics, no, seclusion for life. ”

The body of mollusks is soft, the body is wrapped with a mantle, generally with shells, some shells are degenerate, the body is not segmented, can be divided into three parts: head, feet, and internal organs, and there is a mantle outside the body, and the shape of the feet has its own characteristics, such as the axe feet of river mussels, the gastropods of snails, and the brachiopods of squid

The system is symmetrical from left to right, the body is not segmented, there is a mantle, a crust, and the body cavity is a true body cavity, but it is not developed.

Molluscs, like snails and mussels, are protected by a hard shell, and their bodies are extremely soft and frag......ile

The main characteristics of mollusks are that the body is soft and not segmented, and it is generally divided into heads and feet (some heads are vestigial or disappear; foot muscular) and visceral-mantle (composed of dorsal visceral mass, mantle, and mantle cavity).

The habitat of mollusks is very vast, from tropical continents to the oceans of the Arctic and Antarctic, from highland ponds above 7,000 meters above sea level to the deep sea below 800 meters. There are many species of mollusks, second only to arthropods, with more than 100,000 species extant.

They vary greatly in morphology, but both have soft bodies. Most of them live in the ocean, and only some bivalves and gastropods migrate to brackish and freshwater to inhabit.

Body Divisions

The body of mollusks can generally be divided into three parts: head, feet and internal organs.

1. Head. Located at the front of the body. Agile species, the head is clearly differentiated, and there are sensory organs such as eyes and antennae, such as snails, snails and squid; Slow-moving species have underdeveloped heads, such as turtles; Burrowing or sedentary species, the head degenerates and disappears, such as mussels, oysters, etc.

2. It is usually located on the ventral side of the body and is a locomotor organ, which often has different shapes due to the different lifestyles of animals. Some have well-developed feet that are leaf-shaped, axe-shaped or columnar, and can crawl or dig sediment; Some feet degenerate and lose their motor function, such as scallops.

sedentary species, on the other hand, are inadequate, such as oysters; Some feet have been specialized into wrists, born on the head, and are predatory organs, such as squid and octopus, called cephalopods; A few species of pods specialize in the lateral part of the foot (i.e., parapodium) into sheets that can swim and are called pteropods, such as pteropoda.

3. Visceral mass.

The visceral mass is the part of the internal organ that is usually located on the dorsal side of the foot. Most species of visceral masses are symmetrical, but some twist into a spiral shape and lose their symmetry, such as snails.

Molluscs include snails, mussels, snails, cockles, and squid.

Clams, oysters, scallops, mussels.

Nautilus, coral, razor clams, abalone, jellyfish, nudibranchs.

Sea anemones, tube worms, etc. Molluscs, also known as shellfish, are the collective name of molluscs and are the largest group of animals except arthropods, with about 100,000 species. <

Molluscs include snails, octopuses, mussels, snails, cockles, squid, oysters, scallops, mussels, nautilus, corals, razor clams, abalone, jellyfish, nudibranchs, sea anemones, tube worms, etc. Molluscs, also known as shellfish, are the collective name of molluscs and are the largest group of animals except arthropods, with about 100,000 species.