How are animals classified?
The shape of coelenterates is very strange. They look like plants rather than animals. For example, anemones are like blooming flowers, corals are like willow branches dancing in the water, and corals are like unkempt fences ... There are about 10000 species of coelenterates in the world, most of which are distributed in warm shallow waters, and only corals live in fresh water. Although coelenterates are different in size and shape, they are all cavities formed by two layers of cells in structure, one end is closed and the other end is a mouth with tentacles.
Generally speaking, coelenterates have two basic forms: one is hydra, which adapts to a fixed life; One is jellyfish, which is suitable for floating life.
Jellyfish is a general term for coelenterates of jellyfish. There are many kinds of jellyfish, most of which are umbrella-shaped and have many tentacles and sensory organs. Jellyfish can be divided into two types: small hydra jellyfish and large bowl jellyfish, among which peach jellyfish belonging to hydra jellyfish and Haiyue jellyfish belonging to bowl jellyfish are more representative.
Hydra is the only coelenterate that lives in fresh water. Its cylindrical body is usually attached to aquatic plants, stones and other objects in the water. At one end of Hydra's body, there is a bottom plate on which Hydra slides and moves. Hydra can also do somersaults. At the other end of the hydra is its mouth, with 5-6 tentacles. In addition, the body of hydra has the function of regeneration.
There are about 65,000 species of corals, which are widely distributed coelenterates and all live in the ocean. Coral is mainly found in tropical shallow water. They are the main producers of coral reefs. Coral has tentacles, which are used to catch small animals. Some corals can secrete calcareous exoskeletons, which accumulate slowly in the ocean to form beautiful coral reefs.
Anemones are typical coelenterates. It has many tentacles. The number of these tentacles varies with the species of anemones, but they are all multiples of 6. When the antenna is stretched, it looks like a sunflower, hence the name. Anemone is a beautiful marine life. There are many kinds of anemones, most of which live in crevices or mud, and some are born on shells or crab claws. Common anemones are yellow anemones and green anemones. Coelenterates have a variety of reproduction methods, including budding reproduction, splitting reproduction and sexual reproduction.
There are many kinds of snail mollusks, but their structures are generally simple. Their bodies are soft and symmetrical, and generally consist of five parts: head, feet, viscera, mantle and shell, commonly known as shellfish. Because of different species, the ecological habits of mollusks are also different. Molluscs have four lifestyles: swimming, floating, benthic and parasitic. Mollusks are of great value to human beings. Some are delicious, nutritious and high in edible value; Some can be used as important medicinal materials; Some can make good industrial raw materials. Molluscs play an important role in people's life and production.
The shell of a mollusk is divided into three layers from the outside to the inside. The outer layer is the stratum corneum, and its function is to protect the calcium inside from being eroded by moths. The middle layer is prismatic layer, and the main component is calcium carbonate. The inner layer is nacre, which is wrapped by mantle. Its shell thickness can be continuously increased.
The germ cells of mollusks are all formed by epidermis. Some eggs are produced independently in a free state, and some are adhered by colloidal substances to form egg groups and fixed on objects. Fertilized eggs usually hatch in vitro, but there are exceptions, such as mussels hatching in the gill cavity of mother mussels, while snails are born directly after they are fully developed.
Octopus is also called octopus. Octopus has a big head with eight wrists on it, so it is also called "octopus". Most of them live in gravel or rocks in shallow water. Because they are very strange, they are often regarded as the representative images of monsters in literary works.
Squid is a general term for animals in sepiidae. Their bodies are like pockets, their eyes are big, and there are developed ink sacs in their bodies. When they are hurt by the enemy, they can release ink and escape, so they are also called "cuttlefish". Squid can be eaten raw or dried, and its dried product is also called "dried cuttlefish".
Snails are common mollusks in tropical and temperate regions. They have two pairs of antennae on their heads, and their eyes are at the top of the latter pair of antennae. They often live in humid areas, and when they encounter dry environment or hibernate, they will secrete mucus to seal their shells. Snails crawl very slowly and usually feed mainly on green plants.
Scallop is a common shellfish, which is widely distributed in all sea areas of the world, with the most abundant tropical marine species. Scales or small spines are often found on the surface of scallop shells, which are large and nearly round. The scallops are colorful and elegant, and can be used as decorations.
The body structure of arthropods is symmetrical left and right. The body is divided into several sections, and each section has appendages for walking. There are about 1 10,000 species of arthropods in the world, which are the largest species in the animal kingdom, and most of them are insects. It can be said that one out of every three animals in the world is an arthropod. Arthropods are widely distributed, and where there are animals, there are their footprints. Their body structure is completely adapted to the surrounding environment, so they have strong vitality.
Scorpion arthropods are divided into two parts: female and male, and the shapes and sizes of male and female individuals are also different. From larva to adult, there will be different morphological changes. Drones are grown from unfertilized eggs, which is a strange parthenogenesis.
The most striking feature of arthropods is their constant molting. Take cicadas for example. Cicada's bones are exoskeletons, which are necrotic tissues and cannot grow up with the body. They must change their old shells every once in a while and secrete bigger new bones from their bodies. Old bones split from behind, revealing only a new cicada bigger than before. Cicadas have to molt many times before they can grow from larvae to adults.
Arthropods all form respiratory organs directly from the skin, and animals living in water protrude from the skin to form book cheeks; Animals that live on land are book lungs that are sunken inward. Among them, aphids and chigger mites have no respiratory organs at all, and they breathe on the body surface.
Spiders are typical arthropods, generally with four pairs of feet. Their bodies are round or rectangular, divided into head, chest and abdomen, with a thin abdomen in the middle. Spiders have beards on their heads, and male spiders have a seminal vesicle on their beards. Their anal tips are prominent, which can secrete mucus and condense into fine spider silk when exposed to air. Under the eaves or in the corner, spiders often make a sticky web to catch insects that trap them.
Centipede is also called "centipede". The most common is centipede with less thorns. Its body is flat and long, its head is golden, and it has long tentacles and eyes. The body is divided into 2 1 segments, and each segment has two feet. The first pair of feet are called "E feet", which have poisonous glands and can secrete venom. Scolopendra can be made into medicinal materials after drying.
Hermit crab is an arthropod between shrimp and crab, most of which live in snail shells, hence the name "Hermit Crab". Hermit crab's body is composed of head, chest and abdomen, which is generally asymmetric. Hermit crabs have breastplates on their heads and chests, and their bellies are long and soft, so they can curl up in snail shells. Hermit crabs have a pair of pliers, which feed on small animals or dead animals and generally move in shallow waters by the sea.
Shrimp has a large volume, a flat body and a developed abdomen. They are often sold in pairs in northern China, so they are called "prawns". There are 29 species of prawns in the world, most of which live in tropical and subtropical shallow seas. They mainly feed on benthic invertebrates, such as polychaetes, mollusks with small crustaceans and sometimes some small zooplankton.
The grasshopper's body segment consists of three parts: head, chest and abdomen, which is one step more evolved than shrimp and crab. Moreover, each part of them is no longer the superposition of parts with the same function, but has its own unique function, which is in charge of sensation, movement and reproduction respectively, which greatly enhances the adaptability of locusts to the environment.
Echinoderm is named after its unique shape, represented by famous sea urchins, sea cucumbers and other animals. There are about 5,300 echinoderms, mainly distributed in temperate, subtropical and tropical oceans. They are either fixed on the bottom of the sea or floating on the bottom of the sea. Echinoderm's body is symmetrical from left to right when it is young, and it becomes radial symmetry when it is adult. The bones produced by mesoderm protrude to the body surface to form echinoderms.
Echinoderm's skeleton is endoskeleton, which is composed of some calcified small bone fragments. These bone fragments have different shapes or grow into joints, such as starfish and sea lilies; Or grow together like water bottles, such as sea urchins; Or distributed on the body wall, such as sea cucumber. Small bone fragments of echinoderms often protrude from the body surface to form rough echinoderms.
Echinoderm's "water pipe" system consists of several parts, mainly a sieve plate at the back, a downward straight pipe, a reservoir and five radiation pipes. The ends of the radial tubes form pins. This complex system is an important organ of echinoderms, which plays a key role in their movement, eating, breathing, feeling and digging nests.
Starfish is the most common echinoderm on the coast. They extend five wrists from the center of their bodies in the shape of a five-pointed star. Starfish are distributed in every ocean in the world. They live quietly, generally living in the intertidal zone without waves and the deep-water lower layer of coastal waters. There are many kinds of starfish: Roche starfish with five-pointed stars, bread starfish with hats, sand starfish with soft skin, and lotus starfish with lotus leaves.
Sea cucumbers are like worms in the ocean. Its body is worm-like or sausage-like. Sea cucumber has various colors such as black, brown and white, and some kinds of colors are particularly bright, such as Stichopus japonicus. They mainly feed on organic debris and microorganisms in seabed sediments. Sea cucumbers move very slowly on the seabed and cannot move as flexibly as fish. When it meets an enemy or is stimulated, it will spit out its internal organs to confuse the enemy, and it will take the opportunity to escape, so that the sea cucumber will not die, as long as it grows new internal organs after a while.
Sea urchins are spherical, heart-shaped or disc-shaped. Its shell consists of many calcareous bone plates. The shell is covered with many movable thorns, which makes the sea urchin look like a hedgehog, and its internal organs are wrapped in this shell. Sea urchins sometimes rely on these thorns to help them move. Sea urchins usually inhabit the seabed and feed on attached animals, organic debris, and even carrion and animal feces.
Sea lilies once flourished in Paleozoic, but now they have declined. There are two kinds of existing sea lilies: sea lilies with stalks and sea lilies with sea sheep teeth. Sea lilies with stems look like blooming lilies, mostly inhabiting the seabed, and their bodies can be divided into three parts: roots, stems and crowns. Sea ferns mostly live in shallow coastal waters, and their stems only exist in their infancy and will disappear when they grow up. Sea lilies, with their mouths facing up, use their gentle wrists to catch organic matter and tiny plankton.
There are about 40,000 species of chordates, the most in the animal kingdom. Their common feature is that the back of the body has an axial skeleton-notochord. Chordata are divided into three categories: caudate, cephalochordate and vertebrate. Vertebrates are the most evolved species among animals. They have a complete nervous system, mainly composed of the brain and spinal cord in the spinal cavity, including five groups: fish, amphibians, reptiles, birds and mammals. Each group has a special morphological structure and a special way of life.
Amphioxus belongs to Cephalotaxus, which has notochord, dorsal neural tube and pharyngeal branchial fissure. They have no scales, no obvious sensory organs such as head, eyes, ears and nose, and no special digestive system. Amphioxus is a transitional type from invertebrates to vertebrates, and is called "the ancestor of fish".
Salmon is a carnivorous fish, which feeds on small fish and plankton in the ocean. Its body is long and flat, and its mouth is prominent and slightly curved, shaped like a bird's mouth. Salmon is fierce, but it is also a kind of edible fish. They are large, with a body length of about 0.5 ~ 1 m and a maximum weight of over 6.5 kg. They are delicious in meat, rich in fat and high in nutritional value of fish eggs. So salmon is also a relatively precious large-scale economic fish.
The biggest feature of chordates is that they have soft and elastic chords composed of connective tissues. The notochord can support the body of this kind of animal, which is generally located on the back of the animal's body, above the digestive tract and below the dorsal nerve canal.