In the biological world, there are more than 10 million species of animals, and there are currently 1.3 million species of animals known to humans. Scientists classify these animals into kingdoms, phylums, classes, orders, families, genus, and species in ascending order. We can generally divide animals into: coelenterates, molluscs, arthropods, echinoderms, and chordates (including birds, reptiles, etc.).
The shape of coelenterates is very strange, looking like plants rather than animals. For example, sea anemones are like blooming flowers, hydras are like willow branches dancing in the water, and corals are like shaggy fences... There are about 10,000 kinds of coelenterates in the world, most of them are distributed in warm shallow seas, and only hydras live in fresh water. . Although coelenterates vary in size and shape, they are all structurally a cavity formed by two layers of cells, with one end closed and the other end a mouth with tentacles.
Generally speaking, coelenterates have two basic forms: one is the polyp type, adapted to a stationary life; the other is the jellyfish type, suitable for a floating life.
Jellyfish is the collective name for jellyfish-type coelenterates. There are many types of jellyfish, most of which are umbrella-shaped in shape and have many tentacles and sensory organs. Jellyfish can be divided into two categories: small polyps and large bowl jellyfish. Representatives of these are the peach blossom jellyfish, which belongs to the polyps, and the moon jellyfish, which belongs to the bowl jellyfish.
Hydra is the only coelenterate that lives in fresh water. Its cylindrical body is usually attached to aquatic plants, rocks and other objects in the water. There is a base plate at one end of the polyp's body, and the polyp relies on this base plate to attach to objects and slide around. Hydras can also do somersaults. The other end of the hydra is its mouth, which has 5 to 6 tentacles. In addition, the body of hydra also has a regenerative function.
There are about 65,000 species of coral polyps, which are widely distributed coelenterates and all live in the ocean. Corals are mainly found in shallow tropical seas. They are the main producers of coral reefs. Coral polyps have tentacles that they use to catch small animals. Some coral polyps can secrete calcium exoskeletons, which slowly accumulate in the ocean to form beautiful coral reefs.
The sea anemone is a typical coelenterate with many tentacles. Different types of sea anemones have different numbers of tentacles, but they are all multiples of 6. When the tentacles are extended, they look like sunflowers, hence the name. Sea anemone is a very beautiful sea creature. There are many kinds of sea anemones, most of which live in rock crevices or mud, and some live on shells or crab claws. Common ones include yellow anemone, green anemone, etc. Coelenterates have multiple modes of reproduction, including budding, fission and sexual reproduction.
There are many kinds of snail molluscs but their structures are generally simple. Their bodies are soft and symmetrical. They are generally composed of five parts: head, feet, visceral sac, mantle and shell. They are commonly known as shellfish. Depending on the species, the ecological habits of molluscs are also different. Molluscs have four lifestyles: swimming, planktonic, benthic and parasitic. Molluscs are highly valuable to humans. Some of them are delicious, nutritious, and have high edible value; some can be used as important medicinal materials; some can be used as good industrial raw materials. Molluscs can play an important role in people's lives and production.
The shell of a mollusk is divided into three layers from the outside to the inside. The outer layer is the cuticle, which protects the calcium inside from borers. The middle layer is the prism layer, whose main component is calcium carbonate. The inner layer is nacre, which is surrounded by the mantle. The thickness of its shells can continue to increase.
The germ cells of molluscs are all formed from the epidermis. Some eggs are produced singly in a free state, while others are adhered to by a gelatinous substance to form egg groups and fixed on objects. Fertilized eggs usually hatch outside the body, but there are exceptions. For example, small river mussels hatch in the mother's gill cavity, while small field snails are born directly after they are fully developed.
Octopus is also called "octopus". The octopus has a large head and eight arms on it, so it is also called "octopus". They mostly live in the gravel or rocks of shallow seas. Because they look very weird, they often appear in literary works as representative images of monsters.
Squid is the collective name for cuttlefish. Their body is like a pocket, their eyes are large, and they have well-developed ink sacs in their bodies. They can release ink to escape when they encounter enemies, so they are also called "cuttlefish". Cuttlefish can be eaten fresh or dried. Its dried products are also called "dried cuttlefish".
Snails are a common mollusc in tropical and temperate regions.
Their heads have two pairs of antennae, and their eyes are on the top of the latter pair. They often live in humid areas. When encountering dry conditions or hibernating, they secrete mucus to seal the mouth of their shells. Snails crawl very slowly and usually feed mainly on green plants.
Scallop is a common shellfish that is widely distributed in various sea areas of the world, with the most abundant species in tropical oceans. The shells of scallops are larger and nearly round. There are often radiating ribs on the surface of the shells, and there are scales or small spines on the ribs. The shells of scallops are brightly colored and very beautiful, and can be used as decorations.
The body structure of arthropods is symmetrical, and the body is segmented, and each segment has appendages for walking. There are approximately more than 1 million species of arthropods in the world, making them the most diverse phylum in the animal kingdom, most of which are insects. It can be said that one out of every three animals in the world is an arthropod. Arthropods are widely distributed. Wherever there are animals, there are their footprints. Their body structure is fully adapted to the surrounding environment, so they have strong vitality.
Scorpion arthropods are divided into female and male parts, and the shapes and sizes of male and female individuals are also different. From larvae to adults, different morphological changes occur. Drones grow from unfertilized eggs, which is a strange form of parthenogenesis.
The most striking feature of arthropods is that they constantly shed their skin. Take cicadas as an example. The skeleton of cicadas is an exoskeleton, which is a dead tissue. Therefore, it cannot grow as the body grows. It must Every once in a while, the old shell is replaced and a new, larger skeleton is secreted from the body. The old skeleton splits from the back, and a new cicada, only slightly larger than the original one, emerges. A cicada needs to molt many times before it can grow from a larva to an adult.
The respiratory organs of arthropods are formed directly from the skin. Animals living in water have skin that protrudes outward to form gills; animals living on land have book lungs that are sunken inward. Among them, aphids and chiggers have no respiratory organs at all, they breathe through the surface of their bodies.
Spiders are typical arthropods. They generally have 4 pairs of legs. Their bodies are round or oblong and are divided into cephalothorax and abdomen. In the middle is a very thin abdomen that joins the two parts. . The spider has pedipalps on its head, and there is a sperm vesicle on the pedipalps of the male spider. The tip of their anus is protruding and can secrete mucus, which can condense into fine spider silk when exposed to air. Under the eaves or in corners, spiders often build sticky webs to catch small insects that cast themselves into the web.
Centipedes are also called "centipedes". The most common one we see is the Centipede Centipede. It has a long and flat body, a golden head, long antennae and converging eyes. The body is divided into 21 segments, each segment has a pair of legs, the first pair of legs is called "jaw legs", which have venom glands that can secrete venom. Centipedes can be made into medicinal materials after drying.
Hermit crabs are arthropods between shrimps and crabs. Most of them live in snail shells, hence the name "hermit crab". The body of a hermit crab consists of two parts, the cephalothorax and abdomen, which are generally asymmetrical from left to right. Hermit crabs have a cephalothorax with a long cephalothorax, and a long and soft abdomen that can be curled in the snail shell. Hermit crabs have a pair of chelicerae and feed on small or dead animals. They usually move in shallow waters near the sea.
Prayfish are larger in size, with a flat body and a well-developed abdomen. Often sold in pairs in northern China, they are called "prawns". There are 29 species of shrimps in the world. Most of them live in tropical and subtropical shallow seas. They mainly feed on invertebrates on the seabed, such as polychaetes, small crustaceans, molluscs, etc., and sometimes also prey on some small planktonic animals. animal.
The body segments of locusts are composed of three parts: head, thorax and abdomen, which is one step further evolved than shrimps and crabs. Moreover, each of their body segments is no longer a partial superposition of the same functions, but each has its own unique role, responsible for sensation, movement and reproduction. In this way, the locust's ability to adapt to the environment has been greatly enhanced.
Echinoderms are named for their unique shapes, represented by the famous sea urchins, sea cucumbers and other animals. There are about 5,300 existing species of echinoderms, mainly distributed in temperate, subtropical and tropical oceans. They are either fixed on the seabed or floating on the seabed. Echinoderms have bilaterally symmetrical bodies when young and become radially symmetrical as adults. The bones produced by the mesoderm protrude toward the body surface to form the echinoderm.
The skeleton of echinoderms is an endoskeleton, which is composed of some small calcified bone fragments. These bone fragments have different shapes, or they grow into joints, such as starfish and crinoids; or they grow together like a water bottle gall, such as sea urchins; or they are distributed in the body wall, such as sea cucumbers.
The small bone fragments of echinoderms often protrude from the body surface, forming a rough echinoderm.
The "water pipe" system of echinoderms consists of several parts, mainly the sieve plate on the back, a downward straight pipe, a water reservoir and five radial pipes. The ends of the radial tubes form tube feet. This complex system is an important organ of echinoderms and plays a key role in their movement, feeding, breathing, sensing and nest digging.
Starfish are the most common echinoderms on the seashore. They have five arms extending from the center of their bodies, forming a five-pointed star shape. Starfish are distributed in all oceans around the world. They live a peaceful life, usually in the deep water substratum of waveless intertidal zones and offshore waters. There are many types of starfish: there are five-pointed star-like Roche starfish, there are hat-like bread starfish, there are soft-skinned sand starfish, there are lotus leaf starfish that are shaped like lotus leaves, etc.
Sea cucumbers are like bugs in the ocean. Its body is worm-shaped or sausage-shaped. Sea cucumbers come in various colors such as black, brown, and white. Some species are particularly brightly colored, such as sea cucumbers. They mainly feed on organic debris and microorganisms in seafloor sediments. Sea cucumbers move very slowly on the seabed and cannot move flexibly like fish. When encountering an enemy or being stimulated, they will spit out their internal organs to confuse the enemy and then take the opportunity to escape. In this way, the sea cucumber will not die and will grow again after a while. New entrails.
Sea urchins have spherical, heart-shaped or disc-shaped bodies. Its shell is made of many calcareous bony plates tightly fused together. The shell is covered with many movable spines, making the sea urchin look like a hedgehog, and its internal organs are enclosed in this shell. Sea urchins sometimes rely on these spines to help them move. Sea urchins usually live on the seafloor and feed on attached animals, organic detritus, and even carrion and animal feces on the seafloor.
Crinoids were once very prosperous in the Paleozoic Era, but have now declined. Existing crinoids are divided into two types: crinoids and crinoids. The appearance of sea lilies is very similar to that of blooming lilies, and they mostly live on the seabed. Their bodies can be divided into three parts: roots, stems, and crowns. Sea ferns mostly live in shallow coastal seas, and their stems are only in their infancy. It exists and will disappear when you grow up. The mouth of the crinoid is upward, and it uses its gentle wrists to capture organic matter and small plankton.
There are about 40,000 species of chordates, which are the most advanced phylum in the animal kingdom. Their unique feature is the presence of a central axial skeleton - the notochord - on the back of the body. Chordates are divided into three categories: urochordates, cephalochordates and vertebrates. Vertebrates are the most evolved species among animals. They have a complete nervous system, which is mainly composed of the brain and the spinal cord in the spinal cavity. They include five groups: fish, amphibians, reptiles, birds and mammals. Each group has It has a special morphological structure and a special way of life.
Amphioxus belongs to the phylum Cephalochordates and has a notochord, dorsal neural tube and pharyngeal gill slits. They have no scales, no obvious sense organs such as heads, eyes, ears, and noses, and no specialized digestive systems. Amphioxus is a transitional type of evolution from invertebrates to vertebrates and is called the "ancestor of fish".
Salmon is a carnivorous fish that feeds on small fish and plankton in the ocean. Its body is long and flat on the sides, and its mouth is protruding and slightly curved, shaped like a bird's beak. Salmon has a ferocious temperament, but it is also a food fish. They are large in size, with a body length of about 0.5 to 1 meter, and a maximum weight of more than 6.5 kilograms. Their meat is delicious, rich in fat, and their eggs have high nutritional value. Therefore, salmon is also a relatively rare large-scale economic fish.
The biggest feature of chordates is that they have a soft and elastic notochord composed of connective tissue. The notochord can support the body of this type of animal. It is generally located on the back of the animal's body, above the digestive tract, and on the back. underneath the neural tube.