invertebrate

Biological terminology

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invertebrate^[1] （ Invertebrate ）It's not on the back side spine They are primitive forms of animals. The number of its species accounts for 95% of the total number of animal species. It is distributed all over the world, and there are about 1 million species. include protozoan 、 Echinoderma 、 Molluscs 、 Flatfish 、 Annelida 、 coelenterate 、 Arthropoda 、 Linear animal Etc.

zoology A branch of science. In animal classification, vertebrates and invertebrates are classified according to whether there are vertebrates in the animal body. Study the classification, morphology, physiological characteristics, geographical distribution reproduction The science of evolution is called Invertebrate zoology 。 Invertebrate zoology includes: Protozoology 、 Vermiology 、 entomology 、 Molluscology 、 Crustacean zoology Etc.

Chinese scientific name: invertebrate
Latin name: Invertebrate
circles: Animal kingdom

Distribution area: around the world
Interpretation: Animals without dorsal spine
Discipline: Invertebrate zoology

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brief introduction

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Experimental pictures of invertebrates (8 sheets)

Invertebrates refer to the lower animal groups without vertebrae. Corresponds to vertebrates. Both types and quantities are very large. From the perspective of living environment, there are traces of them in oceans, rivers, lakes, ponds and marshes, as well as on land; In terms of lifestyle, there are free life, parasitic life and symbiotic life; From the way of reproduction, some species can conduct asexual reproduction, some species can conduct sexual reproduction, some species can conduct both asexual reproduction and sexual reproduction, and some species can also conduct larval reproduction, parthenogenesis, etc. According to its evolutionary order, it can be divided into protozoa, sponges, coelenterates, flatworms, linear animals, annelids, molluscs, arthropods, echinoderms and other groups^[2] 。

classification

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Biological classification

They are the original form of animals Vertebrate General term for all departments except for. Just like BBC host David Attenborough Sir David Attenborough said: "If all vertebrate Disappeared from the earth, the world will still safe and sound But if invertebrates disappear, the whole Terrestrial ecosystem Will collapse. "

All invertebrate animals account for more than 95% of the existing animals. It is distributed all over the world, ranging from protozoa to giant squid. Generally, the body is soft and can attach to the inner skeleton of muscles, but there are often hard exoskeletons (such as most mollusks Crustacea And insects) to attach muscles and protect the body. Apart from the lack of vertebrae, invertebrates have little in common. Invertebrate taxonomy Nouns were formerly used as opposed to vertebrates (the word is still the name of a subphylum), but they are no longer used in modern classification. There are more than 20 times more invertebrates than vertebrates on the earth. Invertebrates are an incredibly diverse animal species. They have no common characteristics, only a little different kinship. There are many kinds of animals. People can only find them in the sea, but some kinds, such as insects, live on land and exist worldwide.^[3]

From Swedish biologist Linnai After naming the organism, biologists later used circles （Kingdom）、 door （Phylum）、 Outline （Class）、 order （Order）、 section （Family）、 genus （Genus）、 species (Species). The top boundaries are Prokaryote 、 protista 、 Mycelia 、 Flora And the animal kingdom. From the "boundary" at the top to the "species", the lower the level, the more similar the characteristics of the belonging creatures are.

The animal kingdom is generally divided into ten phyla, including: Protozoa 、 Porifera 、 Coelenterata 、 Platyhelminthes 、 Linear Fauna 、 Annelida 、 Mollusca 、 Arthropoda 、 Echinodermata 、 Chordate 。 Chordate is divided into Caudal cord , head cable, half cable vertebrate The four subphyla, except vertebrates, are invertebrates.

Morphological classification

If classified by morphology, invertebrates are first classified into Unicellular animal (Protozoa) and multicellular animals (i.e Metazoan Metazoa). The animals to which the former belongs are controversial. For example, eye worms chloroplast Is classified as a plant. Multicellular animals are further divided into Lateral animal (Parazoa) and Eumetazoan （Eumetazoa）。 The former includes Sponge animal , Platyclads and Mesozoa 。 These three animals are lack of contact with the true metazoans, and the degree of tissue differentiation is low. Next, true metazoans are divided into Radiosymmetrical animal and Bilaterally symmetrical animal 。 The former includes Cnidaria and Ctenophora 。

Genetic classification

Classification by genetics and morphology Classified entry and exit are in bilaterally symmetrical animals.

Protostome Then it will be divided into two types according to the molting hypothesis: Molting animal and Crown rotifer 。 Molting animals are characterized by Ecdysone (Ecdyson) will remove the cuticle skin on the body surface. Arthropods, linear animals Slow-moving animal and Clawed animal They are molting animals. Crown ring animals are characterized by their development going through the trochlear larva stage (but some animals do not go through the larva stage during their development. A good example is earthworm ）Or yes Tentacle crown 。 Mollusca, Annelida Nugulata （Nemertea）、 Asterozoa （Sipunculida）、 Urechis （Echiura）、 Scutellaria （Pogonophora）、 Bryozoa （Bryozoa）、 Phylum Entoprocta （Entoprocta）、 Brachiopoda (Brachiopoda) and Broomworms (Phoronida) all belong to this crown wheel animal. This classification method has no morphological taxonomic problems. However, there are also some minor issues, such as the controversial classification position of clawed animals (located between molting animals and crown rotifers).

Classification basis

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① The invertebrate nervous system is in the form of a cord Alimentary canal The ventral surface of; and vertebrate It is tubular and located at the back of the digestive tube.

② Invertebrate heart Located at the back of digestive tube; Of vertebrates located on the ventral surface of the digestive tract.

③ Invertebrates have no bones or only Exoskeleton , no real Endoskeleton And vertebrae; Vertebrates have internal bones and vertebrae.

1822 Lamarck, J · - B.de The animal kingdom is divided into vertebrates and invertebrates. 1877 German scholar Heikker take Balanoglossus 、 Ascidian 、 amphioxus Such animals and vertebrates are collectively referred to as chordate, which is in parallel with each phylum of invertebrates classification system Descending to a subphylum of Chordata Hemichorda (Stigma) Urochordata (ascidians) and Cephalochordata (Amphioxus) tied. Since the 1970s, hemichords have become a separate phylum. Since the last three groups belong to the category of invertebrates, invertebrates actually include all animal phyla except vertebrates, which is a general name in zoology rather than a formal name Classification order 。

Classification

The species of invertebrates are very diverse, with more than 1 million species (about 50000 vertebrates) extant, and more extinct species; The number of phyla it includes is increasing with the development of zoology. Due to the more detailed research on various aspects of animals and the deeper understanding of their kinship, the classification status of various phyla often changes. Invertebrates are classified according to morphology and 18s rRNA There are two kinds of sequence classification.

Morphological classification

The multicellular animals are further divided into lateral animals (Parazoa) and true metazoans (Eumetazoa). Then press the bilaterally symmetrical animal Coelom There are three types of "yes", "no", "yes" and "no" Coelomatous animal （Acoelomata）、 Pseudocoeloma (Pseudocoelomata) and Eucoeloma （Eucoelomata）。 However, Nugulata is between pseudocoelomorphs and true coelomorphs, and its classification position is questionable. The representative of the coelomatous animals is flatworms. The coelom of an animal is not Mesoderm Wrapped, yes Gastrula Incomplete degradation products, representing animals are Nematode and Rotifer 。 The coelom of an animal is enclosed by the mesoderm.

According to the development of Blastoporus, the coelomorphs can be divided into protostomia Hindmouth (Deuterostomia) and transition type Tentacle （Tentaculata）。 The representatives of hindmouth animals are Echinoderma (and non "invertebrate" Chordate ）。 Transition types include Broomworm 、 Brachiopods and Bryozoan Three. Other eucoelomorphs are protostomes, including arthropods, bradytes, clawed animals, molluscs Starworm Urechis, annelids, etc.

There are many problems with this classification, such as Nugulates The flatworms and nematodes are protostomes, but they are not qualified to be classified because their body cavities are not "true body cavities". The tentacled animals have many characteristics of hindmouth animals, such as radiation cleavage , body cavity is composed of Endoderm Encapsulated by the mesoderm formed by invagination. But the evidence from molecular biology shows that they are protozoans.

Genetic classification

Macrobenthic invertebrates

The difference between genetic classification and morphological classification lies in bilaterally symmetrical animals. According to the genetic classification, bilaterally symmetric animals are first divided into protostomes and hindstomes according to the development trend of the gastrulae. The transitional tentacled animals in morphological classification are all classified into protostomes.^[4]

morphological character

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Most invertebrates are small, but mollusca Cephalopoda The animals of the genus Sepia have a body length of 18 meters, a wrist length of 11 meters, and a weight of about 2 tons. Most invertebrates are aquatic, most Marine products , if any Foraminifera 、 Radiolaria 、 Pot jellyfish 、 Coral 、 a squid And echinoderms, all of which are marine, some of which live in fresh water, such as Hydra , some snails 、 Clam Class A and freshwater shrimp and crab, etc. snail 、 Dame They live on wet land. and spider , polyps and insects are mostly Terrestrial animal 。 Most invertebrates live freely. Among aquatic species, the small ones live in floating; Having a body shell or crawling under water (e.g shrimp , crabs), or buried in the bottom sediment (such as Sand silkworm Class A), or fixed on foreign objects in water (such as Barnacle 、 Oysters Etc.). There are also many parasitic species of invertebrates, which are parasitic on the surface or body of other animals and plants (such as parasitic protozoa Trematode 、 Tapeworm 、 Echinococcus Etc.). Some species, such as earthworm Ascaris lumbricoides and Ascaris suum It can bring harm to human beings.^[5]

Body structure

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Motion system

Motion system Including body support and forward.

bones

Invertebrates do not have the spine and narrow bones that support vertebrates at the back. In a broad sense, bones include exoskeletons (protective effects, preventing water from evaporating), endoskeletons and Water skeleton Three. And invertebrates have these three kinds of bones.

Exoskeleton refers to crustacean and other hard tissues, such as snail's shell, crab's shell, insect's cuticle They are exoskeletons. Endoskeletons are found in vertebrates, hemivertebrates, echinoderms and Porous animal Medium, supporting inside. Endoskeletons of porous animals do not originate from mesoderm. The internal skeleton of echinoderms is composed of calcium carbonate Composed of proteins, these chemical crystals are arranged in the same direction. Water skeleton is the general name of the fluid under slight pressure in the animal body (including flat animals without coelom) and the muscles against it, plus the epidermis and its affiliated cuticle. The main skeletal form of invertebrates. In addition to the above molluscs, other invertebrates except echinoderms and arthropods have water skeletons.

motion

Invertebrates move in a variety of ways: ① move forward with the help of cilia; ② Linear animals without bristles and circular muscles snake through alternate contraction of longitudinal muscles on both sides; ③ The peristalsis of earthworms with bristles, circular muscles and longitudinal muscles. This is achieved by alternating contraction of longitudinal and circular muscles of different segments; ④ stay Seafloor sediment In the middle, a certain segment of the body is expanded to achieve fixation, and the other part of the body is thinned before drilling Starworm ；⑤ Clawed animal Crawling; ⑥ Insect flight (only a few).^[6]

excretory system

Not all invertebrates have Excretory organ Of. Flats, for example, rely on excretory cells located in the epidermal processes protruding inward from the lower epidermis to complete excretion. The common excretory organs of invertebrates are Protonephric duct and Metanephric duct 。

nervous system

The nervous system of invertebrates is not as complex and diverse as that of vertebrates. From the most primitive nerve cells, to nerve cells gathered into ganglia, to the later formation of the brain. Its form has also gone through a process from simple to complex, from diffuse neural networks to ordered neural chains, to the emergence of central and ladder shaped nervous systems. sense organ from Spinocyst Feeling stick (Yes vision and Sense of gravity ）, passing through the "eye" formed by the nerve cell cluster in the head of flat animals, to the insect Compound eye And cephalopods, such as the eyes of cuttlefish (formed by ectoderm), with increasing resolution. This is more conducive for animals to escape from enemies and prey.

digestive system

The echinococcus is barrel shaped, and the mouth and anus are the same opening. his digestive system go by the name of gastrovascular system (Gastrovaskularsystem), which performs digestion and transportation functions just like the intestines of flatworms, because they do not circulatory system 。

The endoparasitic linear animal factory has degenerated, and they absorb nutrients from the host's small intestine by the cephalomes. Most metazoan animals have digestive ducts that run through the whole body Digestive gland And circulatory system for extracellular digestion. The digestive tract usually consists of: mouth, pharynx, esophagus (earthworm, etc., and swollen Crop ）The stomach, intestines, and anus. And bivalves even use gill Filter food.^[7]

circulatory system

The task of the circulation system is transportation. It will respiratory system Oxygen and nutrients in the digestive system are transported to other parts of the body, while metabolic waste is transported to the excretory organs. Invertebrates do not necessarily have a circulatory system, such as the above-mentioned spinocysts, flatworms, slow-moving animals and linear animals. The animals with circulatory system are like the open circulatory system of mollusks (the circulatory system of cephalopods tends to be closed) and the closed circulatory system of annelids. There are many in the body of insects, spiders and other animals Haemolymph 。

respiratory organ

Invertebrates, like other organisms, need to oxidize energy materials to obtain energy, and this process requires the respiratory system to provide oxygen. The most common respiratory organ of invertebrates is the gill. However, the respiratory organ of insects is trachea, which opens on the surface of the body and can be closed (Stigman). They constantly subdivide into the body, and directly transport oxygen to cells without passing through the circulatory system mitochondrion Next, a very effective respiratory system.

reproductive system

Invertebrates reproduce in various ways. First, it can be divided into sexual and asexual. Some animals, such as echinococcus and parasite Linear animals, with Generational alternation Phenomenon. If the animal is Hermaphrodite , self will also appear mating Phenomenon.

Asexual reproduction The common form is Budding reproduction 。 Spinocytic Asexual generation 。 Sexual reproduction is characterized by the combination of germ cells. The reproductive process can be completed by one person alone, but it is more common for two individuals to provide different mating types germ cell To do it together. The former is found in Pork tapeworm The posterior sexually mature segment will be fertilized in the latter segment. Earthworms also occasionally see themselves mating.

When two individuals mate, the two sides are usually Hermaphrodite Earthworms and snails are hermaphrodites, but they only play a gender role in mating. The mating forms of invertebrates are various. Use of both mating sides of earthworm Genital zone (Clitellum). One side's genital belt is facing the other side Genital foramen 。 Party's sperm It is discharged from the male genital pore, goes along its own sperm groove on the body surface to the other's sperm bag (Receptaculum seminis) and is stored, waiting for egg be fertilized 。

male scorpion There is a special reproductive organ called Spermatophore, which contains sperm. It sticks the seminal vesicle to the ground through secretion. The male and female scorpions dance courtship dance, first sweeping the ground with their tails to attract the attention of the female scorpions. Then the two chelate each other and pull each other. The male scorpion will sting the female scorpion with a poisonous needle and release a small amount of toxin to paralyze and enchant the female scorpion. Then the male scorpion sows the seminal vesicle and pulls the female scorpion to make the reproductive part of the abdomen contact the opening of the seminal vesicle to obtain sperm. The female will try to eat the male scorpion during mating. And male Malu Place the seminal vesicle high and leave. The female horse will later find the seminal vesicle and take it away, and then the fertilization process will take place.

Annelid Polychaeta , will use Schizogenesis (Schizogamie), that is, to detach the body part containing germ cells and complete fertilization in water. Snails have "arrows of love" containing calcium carbonate. Both mating partners pass several times Foreplay Is mutual Dawdle (They will have a rest due to fatigue), and both parties will be excited. Then shoot the "arrow of love" to the other party, reach the climax, and exchange germ cells.

Generations change. Take jellyfish as an example, jellyfish (Medusa) will produce polyps through sexual reproduction of sperm egg fusion. The hydra then undergoes asexual reproduction, that is, collateral sprouting and splitting, and becomes a jellyfish again after the stage of stromatophyte and butterfly larva.

Body temperature problem

Invertebrate -- Earthworm (7 sheets)

Because there is no temperature regulating system in invertebrates, the metabolic rate changes with the change of external temperature. Up to higher Chondrichthyes , such as shark It is a warm blooded animal with temperature regulating mechanism. True Thermostatic animal It should start with birds.^[8]

Development history

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Time of occurrence

The emergence of invertebrates on the earth was at least 100 million years earlier than vertebrates. Most invertebrates Fossil See at the paleozoic era Cambrian , there were arthropod Trilobites And brachiopods. Then it developed Paleocephalopods And species of ancient echinoderms. By the end of the Paleozoic era, ancient types of organisms had been extinct on a large scale. mesozoic There are also ancient types of molluscs (such as Ammonites ）At the end of the period, it gradually disappeared, and modern genera and species of molluscs appeared in large numbers. reach Cenozoic era It has evolved into a large number of modern invertebrates, while brachiopods, which flourished in the Paleozoic, have only survived a few representatives (such as Sea bean sprouts ）。

Life explosion

Also called Cambrian life explosion (Cambrian Explosion), known as Paleontology And geology, since Darwin Since the theory of evolution was put forward, it has been puzzling the academic community. About 600 million years ago, geologically known as the beginning of the Cambrian, most invertebrate phyla appeared in a short period of several million years. This kind of invertebrate fossils (arthropods, molluscs, brachiopods, annelids, etc.) with numerous phyla appeared in Cambrian strata almost at the same time and suddenly, but no animal fossils were found in the older strata before Cambrian for a long time, which is called "Cambrian life explosion" by paleontologists, It is called "Cambrian Explosion" for short. It is still listed as one of the "top ten scientific problems" by the international academic community.

Representative organism

Nautilus

stay Ordovician Nautilus is a top predator in the ocean of Trilobites 、 Sea scorpion In that era when marine invertebrates were at their peak, they dominated the whole ocean with their huge size, sensitive smell and ferocious beaks. Nautilus It has experienced hundreds of millions of years of evolution on the earth, but its shape, habits and other changes are very small. It is called“ living fossil ”, studying Biological evolution And paleontology. Nautilus was almost all over the world in the Paleozoic, but it was basically extinct South Pacific There are also six kinds of nautilus in the deep sea.

Graptolite

invertebrate Graptolite yes Ordovician The most strange and special group, since the early Ordovician At the beginning, it has flourished in breeding and is widely distributed. Some are fixed, some are creeping, some are wandering, and some are floating. The Ordovician graptolites are mainly Orthograptolite Family and genus of, such as didymograptus （DIDYMOGRAPTUS）、 phyllograptus （PHYLLOGRAPTUS）、 Tetragraptus （TETRAGRAPTUS）、 Climacograptus (CLIMACOGRPTUS), etc.

jellyfish

Invertebrate fossils (2 sheets)

Jellyfish are invertebrates, belonging to a member of the coelenterata. The coelenterata is the simplest structure of animals, including jellyfish sea anemone , corals and hydras. There are more than 200 kinds of jellyfish in the world's oceans. They are distributed in waters all over the world, whether in tropical waters, temperate waters, shallow water areas, oceans about 100 meters deep, or even fresh water areas. Jellyfish existed 650 million years ago, even before dinosaurs.^[9]