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Invertebrates: different types, definitions, photos, and more

Invertebrates are the most diverse and widespread group of animals on Earth, accounting for the vast majority of species in the animal kingdom. Invertebrates do not have a backbone, and their body structures vary greatly from simple to complex, adapting to a variety of ecological environments.

  • Scientific name: Invertebrata (not a strict scientific classification, only describing animals with invertebrate characteristics)

  • Main characteristics:

    1. Spineless: lack of backbone

    2. Various sizes: From microscopic microorganisms to giant squids, the size range is huge.

    3. Diversity: There are many species, including insects, mollusks, annelids, etc.

    4. Diverse reproduction methods: Includes asexual reproduction and sexual reproduction.

    5. Dominance: Plays an important role in terrestrial, marine and freshwater ecosystems.

  • Ecological role:

    • Decomposer: Promotes nutrient cycling.

    • Food chain base: Provides food for many vertebrates.

    • Pollinator: Insect pollination maintains plant ecosystems.

  • Evolutionary history:

    • Originated from the Cambrian explosion (about 540 million years ago).

    • They are the earliest group of animals to evolve and form the cornerstone of modern ecosystems.


Invertebrate classification table

Invertebrates are divided into several phyla. The following are the main invertebrate phyla and their representative categories.

Classification levelPhylumClassGenusExamples
PhylumPoriferaCalcareaSpongiaLime sponge, glass sponge
CnidariaScyphozoaAureliaJellyfish, anemone


AnthozoaCoralliumRed coral, staghorn coral
PlatyhelminthesPlatyhelminthesTurbellariaPlanariaTurbellaria


TrematodaSchistosomaSchistosoma


CestodaTaeniaPork tapeworm
NematodaSecernenteaCaenorhabditisNematodesRoundworms
AnnelidaAnnelidaPolychaetaNereisNereis


HirudineaHirudoLeech, leech


OligochaetaLumbricusEarthworm
MolluscaMolluscaGastropod (Gastropoda)HelixSnails, snails


BivalviaMytilusMussels, clams


CephalopodaSepiaSquid, octopus
ArthropodaArthropodaInsectaFormicaAnts, butterflies


ArachnidaAraneusSpiders, scorpions


CrustaceaCancerCrabs, shrimps
EchinodermataEchinodermata (Echinodermata)AsteroideaAsteriasStarfish


EchinoideaEchinusSea urchin

Main characteristics and adaptations of invertebrates

1. Body structure

  • Spineless: lack of vertebrae, body structure ranges from simple to complex.

  • Diversity: diverse morphology, ranging from single cells to complex multicellular structures.

2. Respiration and circulation

  • Gas exchange: gas exchange through the body surface or gills.

  • Circulatory system: from none to closed circulatory system (such as annelids)

3. Reproduction method

  • Asexual reproduction: through division or budding (such as sponges).

  • Sexual reproduction: through fertilized eggs.

4. Environmental adaptation

  • Found in the ocean, fresh water and land, it is an important component of the ecosystem.


Evolutionary History of Invertebrates

  1. Cambrian Explosion:

    • Invertebrates originated in the Cambrian period (about 540 million years ago) and diversified rapidly during the Cambrian Explosion.

    • Fossils representing early invertebrates include trilobites and brachiopods.

  2. Ocean Domination:

    • During the Paleozoic Era, invertebrates dominated the oceans, including corals and echinoderms.

  3. Land Invasion:

    • Arthropods (such as insects and arachnids) were the first invertebrates to adapt to life on land.


Ecological roles of invertebrates

  1. Decomposers:

    • Annelids (such as earthworms) decompose organic matter and improve soil.

  2. Food chain base:

    • Insects and plankton are food sources for many vertebrates.

  3. Pollination and seed dispersal:

    • Insects such as bees are important agents of plant pollination.


Invertebrates in the world

1. Marine invertebrates

  • Representative species: Coral (Corallium), Starfish (Asterias), Anemone (Aurelia).

  • Distribution: Mainly distributed in tropical and temperate waters.

2. Terrestrial invertebrates

  • Representative species: Ants (Formica), snails (Helix).

  • Distribution: Adapted to various terrestrial ecological environments.

3. Freshwater invertebrates

  • Representative species: Leech (Hirudo), mussel (Mytilus).

  • Distribution: Distributed in lakes, rivers and wetlands.


Conservation status of invertebrates

  1. Environmental pollution:

    • Chemical pollution and plastic waste seriously affect marine invertebrates.

  2. Climate change:

    • Rising temperatures and ocean acidification pose a threat to coral reefs and marine life.

  3. Overfishing:

    • Commercial fishing puts pressure on invertebrate populations such as shrimp and crabs.

  4. Protection measures:

    • Establish marine protected areas.

    • Study the contribution of invertebrates to the ecosystem.

Invertebrates refer to lower animal groups that do not have backbones. They are the primitive form of animals. Their species account for 95% of the total number of animal species. Distributed all over the world, there are about 1 million species in existence. Including protozoa, echinoderms, mollusks, flatworms, annelids, coelenterates, arthropods, nematodes, etc.

Protozoa Echinodermata Mollusca Platyhelminthes Annelida Coelenterata Arthropoda Nematomorpha Brachiopoda Hemichordata
fleshy acornworm

fleshy acornworm

Balanoglossus carnosus

Hemichordata Level 2

Features:Enterobranchians

The fleshy acornworm (scientific name: Balanoglossus carnosus) is an enterobranchial animal distributed in the coastal areas of the western Pacific and the northeastern Indian Ocean, belonging to the genus Abalanoglossus of the family Balanoglossidae.Included in the "China National Key Protecte...

Brachytongue

Brachytongue

Glossobalanus mortenseni

Hemichordata Level 2

Features:Enterobranchians

Glossobalanus mortenseni (scientific name: Glossobalanus mortenseni) is an enterobranchial animal distributed along the coast of the Sea of Japan and the coast of China. It belongs to the genus Glossobalanus of the family Glossobalanus. It was described and named by Dutch scholar Cornelius Jan van d...

Acorheaded worm

Acorheaded worm

Balanoglossus misakiensis, acorn worm, jade hook

Hemichordata Level 2

Features:Misaki Acornworm has a strong regenerative ability. The front segment of the insect body with snout, collar and gill area can regenerate the rear organs to restore a complete individual.

Balanoglossus misakiensis (scientific name: Balanoglossus misakiensis) is an enterobranchial animal distributed in coastal areas of Japan and China, but in very small numbers. It is distributed along the coasts from the Yellow Sea to the South China Sea in my country. It belongs to the genus Acornic...

Multibrachial Lingula

Multibrachial Lingula

Glossobalanus polybranchioporus

Hemichordata Level 1

Features:Polybrachia is a unique invertebrate in China. It is of great significance to the study of animal system evolution and biodiversity. It is a national first-level protected wild animal in China.

Polyglochiola was discovered by Chinese biologist Zhang Xi and others in 1965, and was named because of its distinctive feature of having many gill pores.Glossobalanus polybranchioporus (scientific name: Glossobalanus polybranchioporus) is an animal of the genus Glossoporidae in the family Acorniced...

Atlatsjapyx atlas

Atlatsjapyx atlas

pa

Features:Wingless, eyeless, slender body, multi-segmented filamentous antennae, with a pair of segmented tail whiskers or unsegmented tail hairpins.

Atlas japyx atlas (scientific name: Atlas japyx atlas) is an arthropod found in Xiangcheng County, Sichuan Province, the People's Republic of China. It is the only species of the genus Atlas japyx in the family Atlas japyx of the order Dicer. At the time of discovery, it was the largest known dichopod insect in the world at that time. This species belongs to the species of the Diceridae family....

Saccoglossus hwangtauensis

Saccoglossus hwangtauensis

Saccoglossus hwangtauensis,Huangdao long-nosed acorn worm, jade hookworm

Features:Light orange body

The snout of the Huangdao long-nosed worm is relatively long, about 1/20 of the total length, hence the name. The snout is oblate and conical, with an obvious or inconspicuous longitudinal groove on each of the central lines of the dorsal and ventral surfaces, extending from the base of the snout to...

Grylloblattella cheni

Grylloblattella cheni

Grylloblattella cheni

Features:

Chen's western cockroach has an ancient origin, which can be traced back to the Upper Lime Period about 300 million years ago. It can be called a "living fossil" of the class Insecta. As an extremely rare insect that ordinary people rarely see, there are only a few museums in the world...