Dictionary > Kingdom Animalia

Kingdom Animalia

kingdom animalia definition and examples

Kindome Animalia
n., [ˈkɪŋdəm ˌæn əˈmeɪ li ə ]
Definition: A taxonomic kingdom comprising all living or extinct animals

Kingdom Animalia Definition

Each person can say that they know of or can name at least one animal. However, do people know that animals are not merely a group but a kingdom? What does Animalia kingdom mean? What defines kingdom Animalia? To define the kingdom Animalia, one must think of it in a biological sense. Kingdom Animalia or just Animalia is a huge kingdom consisting of eukaryotic, multicellular animals that are heterotrophic in nature.

Characteristics of Animalia Kingdom

What are the characteristics of Kingdom Animalia? Members of kingdom Animalia lack a cell wall, which is found in plant cells, despite the fact that they are unable to create their own food, which is one of the most distinguishing traits of plants. The majority of animals, with the exception of a few, are motile, which helps them to successfully respond to stimuli and obtain food, among other things. One can also go more into depth about the structure and reproduction and growth characteristics of animals.

Biology definition:
Kingdom Animalia is a taxonomic kingdom of living and extinct animals. Members of this kingdom are characterized by being eukaryotic, multicellular, heterotrophic, lacking a cell wall, and mostly are motile.

Kingdom Animalia Classification

Let’s find out about the classification of animals. The animal kingdom classification chart helps see clearly the different categories animals are put into. The animal kingdom chart also helps with the different animal kingdom facts that the group possesses.

In general, animals are separated into two groups:

They are, however, separated into various phyla, which will be examined in further depth below.

A. Vertebrates

Vertebrates are all creatures that belong to the Vertebrata subphylum. They are members of the Chordata phylum and have a backbone (vertebrae) (where the spinal cord is located). In addition, they have an internal skeletal system (endoskeleton) to which muscles are joined. Examples of vertebrates are seen in Figure 1 below.

Figure 1: Different types of vertebrates. Image Source: Maria Victoria Gonzaga of Biology Online.

1. Mammalia

Mammary glands, which produce milk for nourishing (nursing) their young in females, a neocortex (a portion of the brain), fur or hair, and three middle ear bones characterize mammals (from Latin mamma, ‘breast’). These features set them apart from reptiles (including birds), from whom they separated about 300 million years ago in the Carboniferous.

There are around 6,400 living mammalian species. Rodents, bats, and Eulipotyphla are the three biggest orders (hedgehogs, moles, shrews, and others). The Primates which consist of humans, apes, monkeys, and others, the Artiodactyla which include cetaceans and even-toed ungulates, and the Carnivora are the next three groups consisting of cats, dogs, seals, and others.

2. Reptilia

Reptiles are the creatures in the class Reptilia, a paraphyletic grouping that includes all sauropsid amniotes save Aves (birds). Turtles, crocodilians, squamates (lizards and snakes), and rhynchocephalians are examples of living reptiles (tuatara). Classified separately from other reptiles, birds are in the classical Linnaean classification system.

Crocodilians, on the other hand, are more closely related to birds than to other extant reptiles, hence recent cladistic categorization schemes include birds inside Reptilia, redefining the term as a clade. Other cladistic definitions drop the name reptile entirely in favor of the clade Sauropsida, which includes all creatures that are more closely related to current reptiles than to mammals. Herpetology is the study of classical reptile orders, traditionally mixed with contemporary amphibians.

3. Amphibia

Amphibians are ectothermic tetrapod animals of the Amphibia class. The group Lissamphibia includes all live amphibians. They live in a broad range of habitats, with the majority of species inhabiting terrestrial, fossorial, arboreal, or freshwater aquatic settings. As a result, most amphibians begin as larvae in water, although certain species have evolved behavioral adaptations to avoid this.

The larvae with gills typically metamorphose into an adult air-breathing species with lungs. Amphibians utilize their skin as a supplementary respiratory surface, and some tiny terrestrial salamanders and frogs lack lungs and rely only on their skin for respiration. They resemble lizards on the surface, but reptiles, like mammals and birds, are amniotes and do not need bodies of water to procreate.

4. Agnatha

Agnatha is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, with both living and extinct species (cyclostomes and ostracoderms). Cyclastomes are the sister group to all vertebrates with jaws, known as gnathostomes. Recent molecular evidence from rRNA and mtDNA, as well as embryological data, substantially support the concept that the cyclostomes, or live agnathans, are monophyletic.

The first fossil agnathans occurred in the Cambrian period, and two families of agnathans still exist today: lampreys and hagfish, with a total of roughly 120 species. Because hagfish lost vertebrae secondarily, they are classified as members of the subphylum Vertebrata; before molecular and developmental data concluded this happening, Linnaeus created the group Craniata (which is still sometimes used as a strictly morphological descriptor) to refer to hagfish plus vertebrates.

5. Osteichthyes

Osteichthyes is a taxonomic group of fish whose skeletons are mostly formed of bone tissue, they are sometimes called bony fish as well. They are distinguished from the Chondrichthyes by their cartilage-based skeletons. The great majority of fish are members of the Osteichthyes order, which is an exceptionally varied and plentiful organization that includes 45 orders, over 435 families, and 28,000 species.

It is the most numerous class of vertebrates on the planet today. Osteichthyes is separated into two groups: ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are around 425 million years old, and they are also transitional fossils, with a tooth arrangement that is intermediate between a shark and bony fish tooth rows.

6. Chondrichthyes

Chondrichthyes is a class of about 1050 extant cartilaginous fishes that includes skates, sharks, rays, and chimeras. The class consists of 12 orders separated into two monophyletic subclasses, the Elasmobranchii (sharks, rays, and skates) and the Holocephali (chimeras).

With just 40 live species of chimera in the sole order Chimaeriformes representing the Holocephali, the great majority of extant chondrichthyans are elasmobranchs grouped into 11 orders. Although previous classifications divided the elasmobranchs into two categories, sharks and batoids (rays and skates), Campagno recognized four unique groupings based on phenetics (overall similarity) and classified them as the four elasmobranch superorders.

B. Invertebrates

In contrast to cartilaginous or bony vertebrates, invertebrates are any animals that lack a vertebral column or backbone. Invertebrates account for more than 90% of all extant animal species. They are found all over the world and include species such as sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squid. Invertebrates are particularly significant as agricultural pests, parasites, or agents for parasitic infection transfer to humans and other vertebrates.

Invertebrates provide food for humans, are essential components of food chains that feed birds, fish, and a variety of other vertebrate species, and play critical roles in plant pollination. Despite providing crucial environmental services, invertebrates are frequently overlooked in wildlife study and conservation, with large vertebrate studies taking precedence.

Furthermore, numerous invertebrate taxa (including many types of insects and worms) are seen purely as pests, and by the early twenty-first century, widespread pesticide usage had resulted in significant population losses among bees, wasps, and other terrestrial insects.

Figure 2: Different invertebrates. Image Source: Maria Victoria Gonzaga of Biology Online.

Levels of Organization

It is interesting to note that despite all animal kingdom species being multicellular, not all of their cellular arrangements abide by this rule. Animal levels of the organization are categorized into the following categories based on cellular organization patterns:

  • The Cellular Level of Organization: Cells in animals with this kind of cell organization are grouped in loose cell aggregates. Sponge organization is a good example of this.
  • Tissue Level Organization: Animal cells exhibit divisions in cell activity. Cells that complete the same job are tissues. Coelenterates is one example.
  • Organ Level of Organization: Tissues of a certain animal group that perform the same function are grouped together to create an organ. Each organ has a distinct purpose. Platyhelminthes is an example. Organ System Level of Organization: Organ system level of organization has been found in animals where organs have been coupled to create functional systems, each system concerned with a certain physiological function. Chordates, Annelids, Mollusks, Echinoderms, and Arthropods are a few examples.
levels of organization
Figure 3: Levels of organizations. Image Credit: I2wp.com.


Certain species, most notably sponges and ameboid protozoans, lack symmetry, having either an irregular shape that varies from individual to individual or one that undergoes continual changes of form. The great majority of creatures, on the other hand, have a distinct symmetrical shape. Animals have four types of symmetry: spherical, radial, biradial, and bilateral.

Body Cavity/Coelom

The coelom (or celom) is the primary body cavity that surrounds and houses the digestive tract and other organs in most animals. It is lined by mesothelium in certain mammals. It is undifferentiated in other species, such as mollusks. Coelom features have previously been used to categorize bilaterian animal phyla into informal groupings for practical purposes.


Acoelomata is essentially a subgroup (or super-phylum) of creatures that lack a real body cavity. The body cavity, also known as a coelom, is a fluid-filled region positioned between the body wall and the digestive system.

The ventral (where the heart, lungs, and intestines, among other things, are placed) and dorsal cavities are two of the greatest examples of human bodily cavities (where the brain and spinal cord are located). The area between the body wall and the intestine in acoelomates is generally made up of mesenchyme (or some muscle fibres) rather than coelomic fluid (the fluid that separates and protects various organs).

Pseudocoelomates (animals that have a false coelom)

A pseudocoelomate is an organism having a body cavity that is not generated from the mesoderm, as is the case with a real coelomate. Since the blastocoel, or cavity within the embryo, becomes the body cavity, a pseudocoelomate is also known as a blastocoelomate. A real coelom is bordered with a peritoneum, which serves to keep fluid from entering the body cavity. The bodily fluids bathe the organs and obtain nutrients and oxygen from the fluid in the cavity in a pseudocoelomate.


Coelomate creatures, also known as Coelomata (sometimes known as eucoelomates – “genuine coelom”), have a bodily cavity called a coelom with a full lining produced from mesoderm called peritoneum (one of the three primary tissue layers). The entire mesoderm lining permits organs to be linked to one another and hung in a certain sequence while still moving freely inside the space. Coelomates make up the majority of bilateral creatures; this includes all vertebrates.

Different Phyla under the Kingdom Animalia

The kingdom organisms are divided into many phylum animals in the kingdom Animalia phylum. What is a phylum? What is it for? A phylum (plural: phyla, not phylums) is a major taxonomic rank below Kingdom. The members of the animal kingdom are categorized into numerous phyla and subpyla. These divisions help to form the animal kingdom hierarchy and include the eukaryotic kingdom chart.

Animal phyla
Figure 4: the Phylum of Kingdom. Image Credit: ResearchGate.net.

1. Kingdom Animalia: Phylum Chordata

A member of the Chordata phylum is called a chordate. At some time during their larval or maturity phases, all chordates have 5 synapomorphies or main traits that separate them from all other species. The five synapomorphies are a notochord, then the dorsal hollow nerve cord, endostyle – which is also known as the thyroid. There are also pharyngeal slits and a post-anal tail. The term “chordate” is derived from the first of these synapomorphies, the notochord, which is important in chordate structure and movement. Chordates are bilaterally symmetric, have a coelom, a circulatory system, and metameric segmentation.

Main characteristics of chordates

Chordates possess very distinct anatomical features.

  • A notochord is a rigid cartilage rod that runs down the interior of the body. The notochord develops into the spine in the vertebrate subgroup of chordates, and in fully aquatic animals, this allows the animal to swim by bending its tail.
  • A neural tube’s dorsal end. This develops into the spinal cord, the major communication trunk of the nervous system, in fish and other vertebrates.
  • Slits in the pharynx. The area of the throat behind the mouth is known as the pharynx. The slits in fish are changed to create gills, but in certain other chordates, they are part of a filter-feeding system that collects food particles from the water in which the animals dwell.
  • The post-anal tail. A powerful tail that extends behind the anus.
  • A type of endostyle. This is a groove in the pharynx’s ventral wall. It generates mucus to capture food particles in filter-feeding animals, which aids in food delivery to the esophagus. It also stores iodine and is thought to be a forerunner of the vertebrate thyroid gland.

2. Kingdom Animalia: Phylum Porifera

Sponges, members of the phylum Porifera (meaning ‘pore bearer,’) are a basic animal group that is related to the Diploblasts. They are multicellular creatures with pores and channels that let water move through their bodies, which are made up of jelly-like mesohyl sandwiched between two thin layers of cells.
Sponges have unspecialized cells that can change into other types and travel between the major cell layers and the mesohyl regularly. Sponges lack neurological, digestive, and circulatory systems. Instead, most rely on a steady flow of water through their bodies to get food, oxygen, and waste removal. Sponges were the first creatures to split out from the last common ancestor of all animals, making them the sister group of all other animals.

3. Kingdom Animalia: Phylum Platyhelminthes

Flatworms, Platyhelminthes, or platyhelminths are a phylum of very basic bilaterian, unsegmented, soft-bodied invertebrates. They are acoelomates (without a body cavity) and lack specific circulatory and respiratory organs, limiting them to flattened geometries that enable oxygen and nutrients to move through their bodies by diffusion. Because the digestive cavity only has one opening for both ingestion (nutrient intake) and egestion (removal of unprocessed wastes), food cannot be processed constantly.

4. Kingdom Animalia: Phylum Cnidaria

Cnidaria is a phylum under the kingdom Animalia that contains approximately 11,000 species of aquatic organisms found in both freshwater and marine settings, with a focus on the latter. Their distinctive characteristic is cnidocytes, which are specialized cells used mostly for prey capture. Mesoglea, a non-living jelly-like substance sandwiched between two layers of epithelium, each roughly one cell thick, makes up their bodies.

5. Kingdom Animalia: Phylum Annelida

The annelids (Annelida, from Latin anellus, “small ring”), often known as ringed worms or segmented worms, are a vast phylum that includes ragworms, earthworms, and leeches. The species live in and have evolved to a variety of ecologies, including some in marine habitats such as tidal zones and hydrothermal vents, some in freshwater, and yet others in wet terrestrial areas.

Annelids are bilaterally symmetrical, triploblastic, and coelomate invertebrates. They have parapodia for movement as well. Most textbooks continue to utilize the conventional classification of polychaetes (nearly all marine), oligochaetes (including earthworms), and leech-like animals.

Since 1997, cladistic research has drastically altered this system, with leeches now considered a subgroup of oligochaetes and oligochaetes considered a subgroup of polychaetes. Furthermore, the Pogonophora, Echiura, and Sipuncula, which were formerly considered different phyla, are now considered sub-groups of polychaetes. Annelids are part of the Lophotrochozoa, a protostome “super-phylum” that also contains molluscs, brachiopods, and nemerteans.

6. Kingdom Animalia: Phylum Mollusca

After the Arthropoda, Mollusca is the second-largest phylum of invertebrates. Mollusks (or molluscs) are the members. There are around 85,000 known species of mollusks. The number of new fossil species is believed to be between 60,000 and 100,000. The fraction of unnamed species is quite high. Many taxa are still understudied.

Mollusks are the most numerous marine phylum, accounting for around 23% of all identified marine creatures. Freshwater and terrestrial environments are where most mollusks are. They are extremely different, not only in terms of size and physical structure but also in terms of behavior and environment.
The phylum is often classified into seven or eight taxonomic groups, two of which are extinct. Cephalopod mollusks like squid, cuttlefish, and octopuses are among the most neurologically sophisticated invertebrates, with the giant squid or gigantic squid being the biggest known invertebrate species. The gastropods (snails and slugs) are by far the most common mollusks, accounting for over 80% of all identified species.

7. Kingdom Animalia: Phylum Arthropoda

Arthropods are invertebrates with an exoskeleton, segmented bodies, and paired jointed limbs. Arthropods are classified as members of the phylum Arthropoda. They are recognized by their jointed limbs and chitin cuticle, which is frequently mineralized with calcium carbonate.

An arthropod’s body plan is made up of segments, each with a pair of appendages. Arthropods have a bilaterally symmetrical body and an external skeleton. To continue developing, they must go through moulting stages, in which they lose their exoskeleton to expose a new one. Some animals have wings. They are a hugely varied group, with up to ten million different species.

8. Kingdom Animalia: Phylum Hemichordata

Hemichordata is a phylum of marine deuterostome organisms that is commonly regarded as the echinoderms’ sister group. They first emerge in the Lower or Middle Cambrian and are divided into two groups: Enteropneusta (acorn worms) and Pterobranchia. Planctosphaeroidea, a third class, is known exclusively from the larva of a single species, Planctosphaera pelagica. Graptolithina, an extinct class, is connected to pterobranchs.

Acorn worms are worm-like invertebrates that live alone. They mainly live in burrows (the earliest produced tubes) and are deposit feeders, however, some species are pharyngeal filter feeders, and the Torquaratoridae family is a free-living detritivore. Many are well recognized for producing and accumulating halogenated phenols and pyrroles. Pterobranchs are filter feeders that live in a collagenous tube structure known as a coenecium.

9. Kingdom Animalia: Phylum Echinodermata

An echinoderm is any marine animal that belongs to the group Echinodermata. Adults include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as sea lilies or “stone lilies,” which have radial symmetry (usually five points). Adult echinoderms can be found from the intertidal zone to the abyssal zone at all ocean depths.

The phylum has over 7,000 extant species, making it the second-largest grouping of deuterostomes (a superphylum) after chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are the biggest phylum with no members in freshwater or on land.

10.  Kingdom Animalia: Phylum Ctenophora

Ctenophora is a phylum of marine invertebrates known as comb jellies that live in seawater all around the world. They are famous for the clusters of cilia they utilize for swimming (often referred to as “combs”), and they are the biggest creatures that swim using cilia.

Adult ctenophores range in size from a few millimetres to 1.5 m (5 ft) depending on the species. Only 100 to 150 species have been verified, and another 25 may yet be incompletely characterized and designated. Cydippids, which have egg-shaped bodies and retractable tentacles fringed with tentilla (“small tentacles”) that are coated with colloblasts, sticky cells that trap prey, are textbook examples.

11. Kingdom Animalia: Phylum Aschelminthes

Archaeocyatha is a taxon of extinct, sessile, reef-building marine sponges that lived during the Cambrian Period in warm tropical and subtropical seas. The Archaeocyatha origin is presently thought to be in East Siberia, where they have been recognized since the beginning of the Cambrian Tommotian Age, 525 million years ago (mya).

They first arose in other parts of the world much later, during the Atdabanian period, and soon diversified into over a hundred families. They were the planet’s earliest reef-building creatures and are a global index fossil for the Lower Cambrian.

Kingdom Animalia examples

Animalia is a kingdom of eukaryotic creatures. Parthenogenesis is the process through which they reproduce sexually or asexually. When you think of animals, you typically think of species from the phylum Chordata, but there are many others.

    • Jellyfish – For millions of years, long before dinosaurs existed, jellyfish have been traveling about on ocean currents. The jelly-like creatures may be found in both cold and warm ocean water, as well as deep-sea and along coasts, and they pulsate with ocean currents. Jellyfish, despite their name, are invertebrates, or organisms without backbones, not fish.


    • Dogs – A domesticated ancestor of the wolf, the dog (Canis familiaris or Canis lupus familiaris) is recognized by an upturned tail. The dog is descended from an extinct wolf, and the current wolf is the dog’s closest living relative. Before the development of agriculture, hunter-gatherers domesticated the dog for the first time some 15,000 years ago. Dogs have increased to a vast number of domestic individuals as a result of their long contact with humans, and they have developed the capacity to live on a starch-rich diet that would be insufficient for other canids. Dogs evolved to be particularly attuned to human behavior over millennia, and the human-canine link has been the subject of much research.


Try to answer the quiz below to check what you have learned so far about Kingdom Animalia.


Choose the best answer. 

1. Which of the following is a characteristic of organisms belonging to Kingdom Animalia?

2. Group of animals with a backbone

3. Animals with a true body cavity

4. Invertebrates with an exoskeleton, segmented bodies, and paired jointed limbs

5. Class of cartilaginous fish species

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