There are about 10000 kinds of sponges known today. Unlike other invertebrates, most sponges live in the ocean, and only a few live in fresh water. Living sponges have a variety of body colors, ranging from brown, orange to purple, and the body height varies from 1-200cm, and the shapes are flat, spherical, barrel-shaped and pot-shaped. Sponge adheres to the bottom of the sea. They use the flagella movement on the inner wall of the body to generate water flow in the water. Water flows into the sponge through numerous water inlet holes (ports) on the porous surface of the sponge, and the food contained in the water is filtered and absorbed before being discharged from the body through water outlet holes (ports). This simple cycle mode is the way for sponges to survive. The physiological structure system of sponge is very simple. At the stage of no organ formation, the system stays at the tissue level. One or more cavities of sponge are radially symmetrical or asymmetrical, and the cavities are composed of two cell layers, namely, the inner cortex and the outer cortex. Their endoskeleton is called spicule or sponge bone, and some species have both. The types of sponges are distinguished according to the shape of endoskeleton, which can be divided into three categories:
1.Calcarea: This kind of sponge is calcium carbonate spicule, which is a relatively primitive species, mostly living independently, distributed in shallow water and intertidal zone of land coast, with about 50 species.
2.xactinellida: This kind of sponge is a silicon bone needle, also known as "glass sponge", with a medium size and lives in the deep sea with a water depth of 500- 1000 meters. Most of them live independently, with about 450 species.
3. Demonpongiae: There are many kinds of sponges in this class, about 9,500 species. Except for a few species, most of them have bones, which are single-or four-release silica spicules, organic sponge fibers or both, but there are absolutely no calcium spicules and six-release silica spicules. A few species are produced in fresh water, and most of them are seafood. They often grow together in groups, and the individual boundaries are unknown. Coelenterates are classified according to the symmetry of their bodies. The coelenterate's body cavity is radially symmetrical, and there is a digestive cavity in the body, which is called "gastric vascular cavity". The cavity has a mouth without anus, tentacles around the mouth and special stinging cells, so coelenterates are also called "CNIDAR". Although coelenterates have simple organs, they are still classified as organized animals in classification.
Coelenterates are divided into three categories:
1. Hydra: This class is the most primitive of coelenterates. Hydra has a very simple body structure. Their body wall consists of only two layers of cells, with a simple stomach cavity and no body cavity separated. They usually live in groups. The germ cells of hydra are formed from ectoembryos, and there is a phenomenon of generation alternation, that is, there are asexual hydra generations and sexual jellyfish generations, and these hydra mothers have marginal membranes. Some polyps secrete calcareous bones, while others turn into jellyfish.
2.Scyphozoa: coelenterates of this class are mainly jellyfish, which can also be collectively called jellyfish. Their jellyfish wings have no marginal membranes and their bodies have three germ layers. Germ cells are derived from endoderm and do not secrete bones. In terms of body structure, jellyfish has an oral arm with stinging cells, which can be used to catch prey and then send it to the mouth. The mouth opens in the center and leads to the stomach sac in the body. The gonad is located on the cyst wall, and there is also the phenomenon of generation alternation. The first generation of corals appeared in the larval stage, while the first generation of jellyfish was more developed.
3. Coral: Common anemones, corals, etc. All belong to this class. The most important feature is that they only have hydra without water, which means they only have hydra generation. The class is divided into two subclasses: Octocorallia: it has eight pinnate tentacles, and its body is divided into eight equal parts, usually with a ditch, which lives in a fixed group and secretes calcium or horny bones. They often appear on the coast of tropical warm waters, such as crocodiles, cockscomb, and sea pens. Hexacorallia: It has six tentacles or multiples of six, almost no branches, an extremely complicated diaphragm, two ciliated tubes and an exoskeleton. Such as anemones, Carnivora, scarabs, etc. All belong to this kind of mollusk (mollusk). Besides radial symmetry, another form of body cavity is bilateral symmetry. As the name implies, mollusks are soft and usually have a protective shell, but some species have degenerated or even disappeared, such as octopus and squid. Their body cavities are not segmented, their abdomen has developed muscular feet, and their shells wrap their bodies. The protective shell is hidden in the coat. Molluscs can be divided into five categories, including all kinds of creatures, such as shellfish with shells, snails with shells, octopus without shells and squid with degenerated shells.
1. Gastropoda: Gastropoda is the second class in the animal kingdom after insects, including snails, live slugs (sea rabbits) and other species. The biggest feature is that the abdomen and feet are combined into a special sports organ. Based on this main feature, Gastropoda is divided into three subclasses: Prebranchial subclass: the gill is located in front of the heart, and the digestive cavity is twisted at 180 degrees, that is, the digestive cavity is U-shaped in adulthood, and the anal opening is in the same direction as the head, which is both sexes. There are a pair of tentacles. This category includes snails from seawater and some fresh water. Post-branchia: the shell is atrophied or completely degraded, and the internal organs are partially twisted or not. They are hermaphroditic and all live in seawater, such as live slugs (sea rabbits). Pulmonary phylum: it has no gills and breathes with its lungs. Mainly live in land and fresh water, only a few live in the ocean. Shells are small in shape, with or without simple spiral, such as snails and freshwater snails.
2. Bivalves: It has two symmetrical shells, headless teeth and tongue, and an axe-shaped gastropod. The thinner part of the body is the ventral surface, and the thicker part of the shell top is the back surface. The two shells are connected by a butterfly hinge. Inside the two shells, there are internal organs surrounded by the outer jacket, and the rear end of the outer jacket is deformed into a water outlet pipe and a water inlet pipe. There are two shell muscles on the shell to control the opening and closing of the shell. They have cilia on the inner surface of mantle and gill surface, which can control the entry and exit of water, thus breathing and filtering life. It is bisexual and has sexual reproduction.
3.Ceohalopoda: Everyone lives in the ocean. Unlike most mollusks, Ceohalopoda is an active carnivore. Not only do they swim fast, but some species even have developed eyes and great wisdom, such as octopus and squid. They can be said to be the most evolved group of mollusks. Cephalopods are divided into two subclasses: Tetrabranchia: it has two pairs of gills and a shell, but its shell is only coiled on one plane and has an open circulatory system and compartments. Nautilus, a living fossil, belongs to this subclass and there are only three different species. Bibranchiata: it has a pair of gills, mesothelium degenerates into a body, adopts a closed circulatory system and has ink sacs. This subclass is divided into two categories: Octopus (whose shell degenerates into body) and Octopus without shell. There are many suckers on the surface of tentacles of squid and octopus, which can be used to catch prey. Besides teeth and tongues, they also have two hard lips to kill their prey. Octopus moves by first filling its sheath with water, and then vigorously spraying water. At this time, the body moves at a high speed in the opposite direction.
4.Scaphopoda: Its name comes from the fact that they have feet that can dig the bottom, but they have no heads and gills, such as ivory shells and so on.
5. Polypodia: It has no tentacles, flat feet, head and flaky shells. Usually it lives on a stone, and it will be firmly adsorbed when it meets the enemy. If annelids are distinguished by their body structure, there are two kinds of segmented body cavities: annelids and arthropods. Their bodies are composed of a series of segments, and their walls and internal organs are segmented. These segments extend horizontally and are separated by a diaphragm. Some types of body segments can reach more than 65,438+000, and other organs can be repeated in each segment except digestive tract and nervous system.
There are about 10000 species of annelids, which are divided into three categories:
1. polychaete: all kinds of tube worms that grow freely in the ocean belong to this category. They have bristles on their bodies, good prostate, eyes and antennae.
2. Oligochaeta: All live in fresh water or soil. There are several bristles on the body, and the head is underdeveloped. They are all hermaphroditic. The representative species is common earthworm.
3. Leeches: They all live in fresh water. They have no diaphragm and appendages, and there are permanent muscle suckers at both ends of the head and tail. The representative species is the common leech (leech) Arthropods The body of most arthropods can be divided into three parts: head, chest and abdomen. Unlike annelids, arthropods are fixed for life, and they are the most diverse in the animal kingdom. The biggest feature is that it has segmented appendages, which are not only used for sports, but also often transformed into organs for swimming, breathing, reproduction, defense and hunting. The exoskeleton of arthropods is composed of chitin, which has the functions of protecting and attaching muscles and preventing water loss in the body. These hard exoskeletons limit the growth, so arthropods need to go through molting many times in the development process and grow rapidly without hardening the exoskeleton. The decapitation of arthropods has also evolved a lot and can become a part of it independently. With an independent head, the sensory organs and nervous system of arthropod forebody become extremely developed, so most arthropods have a pair of complex compound eyes and some equally complex sensory organs.
Arthropoda can be divided into three subfamilies:
1. Trilobite: It is the most primitive arthropod. At present, only their fossils remain. According to these fossils, there are about 4000 different species.
2.Chelicera: The most representative animal is horseshoe crab, which belongs to the order Petalopoda.
3. Crustacea: Crustacea is the only animal that mainly lives in the sea, including all kinds of shrimps and crabs. They play an important role in the marine food chain. They are both primary consumers and primary producers, and they are one of the important food sources for marine fish. Another big class of crustaceans is Inscta, which is the most successful creature on earth. Echinoderm The embryo division and formation of echinoderms are different from the above phylum. Echinoderms, like vertebrates, belong to the retrostomata, while annelids, arthropods and molluscs belong to the protostomata. The difference between them is that the latter is radiation cleavage and the body cavity is formed by mesoderm invagination. Original stoma: spiral cleavage, gastrula cells expand outward to form body cavity, and embryo stoma develops into late stoma. Therefore, the genetic relationship between echinoderms and humans is relatively close. Although there are great differences in appearance and morphology, many evidences will be found from embryology. All echinoderms live in the ocean, and the biggest feature is that they have a water vascular system, which consists of a group of pipes that can circulate seawater. They have developed body cavities, complete digestive system and incomplete circulatory system, and the nervous system is relatively simple with radial nerve fibers.
Echinoderms are divided into five categories:
1. sea lilies: the mouth is upward and there are tentacles around the mouth. There are many branched feathers on the tentacles, which can be used to catch food. The most representative animals are the sea feather star and the sea lily.
2.Asteroidea: the body contains a middle plate, the mouth is located under the middle plate, and there are 5-20 tentacles, and there are many tube feet on the tentacles. All kinds of starfish belong to this category.
3. Ophiuroiidea: It also has a middle disk and tentacles, but its middle disk is thin and long, which obviously stands out from the middle disk and can move faster than starfish. The most representative animal is the sheep's foot.
4. Sea urchins: It has no tentacles, but it has a body shell, from which many spiny spines protrude and are moved by tube feet. All kinds of sea urchins belong to this category.
5. Holothurian: The body is a rotatable muscle bundle with deformed tube feet around the mouth for foraging. Because of their weak action ability, they developed a special self-defense behavior, that is, when attacked by the enemy, they would shoot internal organs from the anus to the enemy and take the opportunity to escape, so that the internal organs could regenerate. All kinds of sea cucumbers belong to this category.