Scientific Classification of Animal Kingdom

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“Taxonomy” means how scientists arrange and group living things based on their similarities and differences. When we say “animal kingdom” or “Kingdom Animalia” we’re talking about a big group of creatures that are all animals. These animals have some things in common, like having many cells (Multicellularity), eating other things for food (Heterotrophy), and being able to move around (Motility) etc. Scientists use the animal kingdom to study and understand animals better. It’s like sorting animals into different groups to make it easier to learn about them.

All Animals are Placed under Kingdom Animalia

In this article, we’ll go on an exciting journey to explore the scientific classification of Animal Kingdom, Chart and characteristics.

taxonomy flow chart animal kingdom

Scientific Classification of Animal Kingdom Phylum

The kingdom Animalia, commonly known as the animal kingdom, is one of the five major kingdoms in the biological classification system. It includes all animals, which are multicellular, heterotrophic organisms that obtain their food by consuming other organisms. Animals are characterized by their ability to move at some stage of their life cycle and by the absence of cell walls around their cells, distinguishing them from plants and fungi. The fundamental basis for the classification of animals in the Animal Kingdom includes Levels of Organisation, Symmetry, Diploblastic and Triploblastic Organisation, Coelom development, Segmentation of the body and presence or absence of Notochord. Animal Kingdom is Divided into 11 Phylums. They are:-

Classification of Animal Kingdom
  • (i) Chordata (Most Advance Animals)
  • (ii) Hemichordata
  • (iii) Echinodermata
  • (iv) Mollusca
  • (v) Arthropoda
  • (vi) Annelida
  • (vii) Aschelminthes
  • (viii) Platyelminthes (Flatworms)
  • (ix) Ctenophora
  • (x) Coelenterata
  • (xi) Porifera ( Most Primitive Animals )

All Animals are Multicellularity

Phylums : Chordata

Chordata is one of the main phyla of animals, the basic form of classification of these animals is the presence or absence of notochord. So, there are two main groups: Chordates and Non-chordates.

classification of Chordata

Chordates

Chordates are a diverse group of organisms that belong to the phylum Chordata. They also have a hollow nerve cord and pharyngeal gill slits. Common characteristic features of Chordates are as follows:

  • Notochord: Chordates have a notochord at some stage during development. Notochord is a flexible, rod-like structure that provides support to the body.
  • Hollow Nerve Cord: Chordates have a hollow nerve cord, a cylindrical structure located on the dorsal (upper) side of the body. In vertebrates, this cord develops into the spinal cord.
  • Pharyngeal gill slits: Chordates usually have pharyngeal gill slits, which open into the throat. These structures may serve a variety of functions, including filter feeding in some chordates.
  • Post-anal tail: Chordates have a post-anal tail, which extends beyond the anus at one point in their development. In many vertebrates, this tail is reduced or modified during embryonic development.
  • Example: Sea Squirts, Fish, Birds and Mammals etc.

The phylum Chordates is divided into three main subphyla, each containing specific groups of organisms with distinct characteristics. Here are the divisions or subphyla within Chordates:

classification of Chordates
Subphylum – Urochordata (Tunicates)

Urochordates are marine animals that are often encased in a hard outer covering called a tunic. Adult tunicates exhibit filter feeding and have a relatively simple body plan.

Characteristic Features of SubphylumUrochordata

  • Urochordates, commonly known as tunicates or sea squirts, are marine animals.
  • They usually have a sac-like body enclosed in a tough outer covering called a tunic.
  • Adult urochordates are sessile, meaning they are attached to a substrate and do not move around.
  • Urochordates exhibit filter feeding, using specialized structures to capture and filter food particles from water.
  • Although adults have a relatively simple body plan, their larval stages more closely resemble those of typical chordates, including the presence of a notochord and dorsal nerve cord.
  • Examples: Ascidians, Doliolum, Oikopleura, etc.
Subphylum – Cephalochordata (Lancelets)

Cephalochordates are small, marine animals that retain many chordate characteristics throughout life. They have a notochord and a dorsal nerve cord but no true spinal column.

Characteristic Features of Subphylum – Cephalochordata

  • Cephalochordates, also known as lancelets or amphioxus, are small marine animals.
  • They retain many chordate characteristics throughout their lives, making them an important group for understanding the evolutionary history of chordates.
  • Cephalochordates have a notochord, dorsal nerve cord, pharyngeal slit, and a post-anal tail throughout the life cycle.
  • They are usually filter feeders, capturing food particles from water using their pharyngeal slits.
  • Unlike urochordates, cephalochordates are capable of active swimming.
  • Example: Amphioxus or lancelet.
Subphylum – Vertebrata (Vertebrates)

Vertebrata are the most diverse and well-known subphylum of chordates. These include animals with well-developed vertebral columns (spines) and complex nervous systems. Vertebrata encompasses a wide range of animals, from fish and amphibians to mammals including reptiles, birds and humans.

Characteristic Features of Subphylum Vertebrata

  • Vertebrata are the most diverse and well-known subphylum of chordates.
  • They are characterized by a well-developed vertebral column (spine or spine) that surrounds and protects the dorsal nerve cord.
  • Vertebrata also has a cranium, which is a bony or cartilaginous structure that encloses and protects the brain.
  • This subphylum includes a wide range of species from fish and amphibians to reptiles, birds and mammals.
  • Vertebrata exhibit a variety of adaptations and complexity and have successfully adapted to terrestrial, freshwater and marine environments.

Vertebrata are further classified into several classes, each containing specific groups of animals. Here is a simplified classification of the subphylum vertebrates:

classification of Vertebrata
Class Agnatha (Jawless Fishes)
  • Example: Lampreys and Hagfishes.
  • These are primitive, jawless fish with a cartilaginous skeleton. They often have a sucker-like mouth.
Class Chondrichthyes (Cartilaginous Fishes)
  • Example: Sharks, Rays, and Skates.
  • These fishes have a skeleton made of cartilage and tough, tooth-like scales. They typically have well-developed jaws.
Class Osteichthyes (Bony Fishes)
  • Example: Perch, Salmon, and Catfish.
  • Bony fishes have a skeleton made of bone. They are the most diverse group of vertebrates and include both freshwater and marine species.
Class Amphibia (Amphibians)
  • Examples: Frogs, Toads, and Salamanders.
  • Amphibians typically undergo a metamorphic life cycle, starting in water with gills and transitioning to land with lungs as adults.
Class Reptilia (Reptiles)
  • Examples: Snake, Turtle, Crocodile, and Lizard.
  • Reptiles are characterized by scaly skin, and most of them lay eggs. They are cold-blooded (ectothermic).
Class Aves (Birds)
  • Examples: Eagles, Penguins, Sparrows, and Owls.
  • Birds are warm-blooded (endothermic) and have feathers, beaks, and hollow bones. They are adapted for flight.
Class Mammalia (Mammals)
  • Example: Humans, Dogs, Cats, Whales, and Bats.
  • Mammals are characterized by having mammary glands that produce milk to nourish their young. They typically have hair or fur and are warm-blooded.

Non-chordates

Non-chordates are animals that do not belong to the phylum Chordata. Unlike chordates, non-chordates lack specific structural features such as a notochord, hollow nerve cord, pharyngeal slit, and a post-anal tail. Common characteristic features of Non-chordates are as follows:

  • Exoskeleton (in some phyla): Many non-chordates, especially in the phylum Arthropoda, have an exoskeleton made of chitin, which provides support and protection.
  • Segmentation (in some phyla): Some non-chordate phyla such as the Annelida exhibit body segmentation with repeated, similar body segments along their length.
  • Bilateral Symmetry: Non-chordates typically exhibit bilateral symmetry, where their bodies can be divided into two equal parts along a central axis.
  • Germ layer: During embryo development, they often have three germ layers (ectoderm, mesoderm, and endoderm), which give rise to different types of tissue.
  • Digestive system: Non-chordates have a complete digestive system, including a mouth and anus, which allows them to efficiently ingest, process and eliminate food.
  • Nervous system: They possess a nervous system, although its complexity varies among different phyla. Some have ganglia or nerve clusters that act as primitive brains.
  • Circulatory system (in some phyla): Certain non-chordates have a circulatory system for transporting nutrients, gases and other substances throughout their body.
  • Respiration: Their breathing patterns are different. Some use gills, others have simple dilation through the tracheal system or their body surface.
  • Reproduction: Non-chordates reproduce by a variety of methods, including sexual reproduction through external or internal fertilization and in some cases asexual reproduction.
  • Larval stage: Many non-chordates undergo metamorphosis, having distinct larval stages before becoming adults.

Different Between Chordates and Non-Chordates

Sl no.ChordatesNon Chordates
1Notochord present.Notochord absent.
2Central nervous system is dorsal,
hollow and single.
Central nervous system is ventral, solid and double.
3Pharynx perforated by gill slits.Gill slits are absent.
4Heart is ventral.Heart is dorsal (if present).
5A post-anal part (tail) is present.Post-anal tail is absent.

Phylums : Hemichordata

Hemichordata comprises a group of marine organisms that show some similarities to both chordates and echinoderms. They are characterized by unique anatomical features that set them apart from other phyla. Some common characteristic features of Phylum Hemichordata:

  • Proboscis: Hemichordates have a proboscis, which is an elongated, tube-like structure that protrudes from the front of their bodies. The proboscis is used for feeding and can be extended and retracted as needed.
  • Collar: They possess a collar region, which is a transitional segment between the proboscis and the trunk. The collar often contains important anatomical structures, including the stomochord.
  • Stomochord: One of the distinctive features of hemichordates is the presence of a stomochord. This tubular structure, located in the collar region, serves as a support for the body, similar to the notochord found in chordates.
  • Trunk: Hemichordates have a trunk region that follows the collar. This part of their body typically contains the digestive and reproductive systems.
  • Pharyngeal Structure: They possess pharyngeal structures that are involved in filter feeding and respiration. These structures are important for their survival in marine environments.
  • Marine Habitat: Hemichordates are exclusively marine organisms, inhabiting various ocean habitats, including the seafloor and the water column.

Phylums : Echinodermata

Phylum Echinodermata includes a diverse group of marine animals known for their spiny skin and unique radial symmetry. These fascinating creatures exhibit several distinctive characteristics that set them apart from other phyla. Some common characteristic features of Phylum Echinodermata:

  • Pentaradial Symmetry: Echinoderms typically display pentaradial symmetry, which means their bodies are arranged in five or multiples of five symmetrical parts. This radial symmetry allows them to orient themselves in various directions without a distinct front or back.
  • Water Vascular System: They possess a unique water vascular system, which is a network of fluid-filled canals connected to tube feet. This system facilitates locomotion, feeding, and gas exchange.
  • Endoskeleton: Echinoderms have an endoskeleton composed of calcium carbonate plates or ossicles embedded in their skin. These structures give them the characteristic spiny appearance.
  • Tube Feet: They use tube feet for various functions, including movement, feeding, and attachment to surfaces. These tube feet are operated by the water vascular system and can be extended or retracted as needed.
  • Regenerative Ability: Echinoderms have remarkable regenerative capabilities, allowing them to regrow lost body parts, including arms and even entire individuals from a single body fragment.
  • Lack of Brain and Eyes: Most echinoderms lack a centralized brain, although they have a decentralized nervous system. They also lack well-developed eyes, relying instead on light-sensitive cells for sensory perception.
  • Dermal Branchiae (Skin Gills): Some echinoderms possess dermal branchiae, which are specialized structures used for gas exchange. These structures extend from the body surface, increasing the surface area for respiration.

Phylums : Mollusca

Phylum Mollusca represents a diverse group of invertebrate animals that inhabit marine, freshwater, and terrestrial environments. Mollusks exhibit a wide range of body forms and adaptations, making them one of the most varied and successful phyla in the animal kingdom. Some common characteristic features of Phylum Mollusca:

  • Soft Body with Muscular Foot: Mollusks typically have a soft body that may be enclosed within a hard shell. They also possess a muscular foot, which is used for various functions such as locomotion and burrowing.
  • Mantle and Mantle Cavity: They have a specialized tissue called the mantle that covers the visceral mass. The mantle often secretes the shell in molluscs that possess one. The mantle cavity houses the gills of aquatic species and serves as a chamber for respiration.
  • Radula: Many mollusks have a radula, which is a specialized feeding organ with rows of tiny teeth. The radula is used for scraping or tearing food particles before ingestion.
  • Shell (in many species): A prominent feature of many molluscs is the presence of a hard external shell that provides protection from predators and harsh environmental conditions. However, not all molluscs possess a shell.
  • Bilateral Symmetry: Mollusks exhibit bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis.
  • Open Circulatory System: They typically have an open circulatory system, where blood or hemolymph bathes the organs directly before being pumped back to the heart.
  • Gills or Lungs: Aquatic molluscs often have gills for respiration, while some terrestrial molluscs have evolved lungs or other specialized respiratory structures.
  • Diverse Feeding Strategies: Mollusks display various feeding strategies, including herbivory, carnivory, filter-feeding, and scavenging, depending on the species and their habitats.

Phylums : Arthropoda

Phylum Arthropoda is one of the largest and most diverse phyla in the animal kingdom, encompassing a wide array of invertebrate organisms. Arthropods are characterized by their segmented bodies, exoskeletons, and jointed appendages. Some common characteristic features of Phylum Arthropoda:

  • Arthropoda: Exoskeleton: Arthropods have an external skeleton, known as an exoskeleton, which provides structural support and protection. This exoskeleton is made of a tough, waterproof substance called chitin.
  • Segmentation: They exhibit a segmented body characterized by distinct body regions, including the head, thorax, and abdomen in many arthropods. This segmentation allows for flexibility and specialized movement.
  • Jointed Appendages: Arthropods have jointed appendages, such as legs, antennae, and mouthparts, which are adapted for various functions such as locomotion, feeding, and sensory perception.
  • Bilateral Symmetry: Most arthropods display bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis.
  • Open Circulatory System: Arthropods typically have an open circulatory system, where blood or hemolymph is pumped into the body cavity, bathing the internal organs directly.
  • Moulting: They undergo periodic moulting, a process known as ecdysis, to shed their exoskeleton and allow for growth. During this process, a new, larger exoskeleton is formed underneath the old one.
  • Diverse Habitats and Lifestyles: Arthropods inhabit diverse ecosystems, including terrestrial, freshwater, and marine environments. They occupy various niches and play essential roles in food webs and ecosystems worldwide.
  • Diverse Species: The phylum Arthropoda includes a vast number of species, such as insects, arachnids, crustaceans, and myriapods, showcasing an incredible diversity of forms, sizes, and adaptations.

Phylums : Annelida

Phylum Annelida comprises a diverse group of segmented worms that can be found in various aquatic and terrestrial environments. Annelids exhibit a range of sizes and shapes, but they share several common characteristic features. Some key characteristics of Phylum Annelida:

  • Metamerism: Annelids exhibit metamerism, which is the segmentation of their bodies into distinct, repetitive segments. Each segment typically contains a set of organs and muscles.
  • Hydrostatic Skeleton: Annelids have a hydrostatic skeleton, which is a fluid-filled body cavity that provides support and enables movement through peristaltic contractions.
  • Longitudinal and Circular Muscles: They possess both longitudinal and circular muscles in their body walls, allowing them to move and contract in different directions.
  • Setae: Many annelids have small bristle-like structures called setae on their body segments, which aid in movement and provide traction.
  • Closed Circulatory System: Annelids have a closed circulatory system, with blood enclosed within vessels, which helps transport nutrients, gases, and wastes throughout their bodies.
  • Well-Developed Nervous System: They have a well-developed nervous system, including a nerve cord and ganglia, which helps coordinate their movements and sensory perception.
  • Bilateral Symmetry: Annelids typically exhibit bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis.
  • Various Lifestyles: Annelids encompass various lifestyles, including marine worms, earthworms, and leeches, each adapted to their specific habitats and ecological niches.

Phylums : Aschelminthes

Phylum Aschelminthes, also known as the pseudocoelomates, encompasses a diverse group of unsegmented, bilaterally symmetrical worms that inhabit various environments. Despite their simple body plan, they exhibit a range of adaptations that have enabled them to thrive in different ecological niches. Some common characteristic features of Phylum Aschelminthes:

  • Pseudocoelom: Aschelminthes have a pseudocoelom, which is a fluid-filled body cavity that is not completely lined by mesoderm. This body cavity provides space for internal organs and allows for the circulation of nutrients.
  • Bilateral Symmetry: They exhibit bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis.
  • Complete Digestive System: Aschelminthes possess a complete digestive system with separate mouth and anus openings, allowing for efficient food ingestion and waste elimination.
  • Cuticle: They have a protective outer covering called a cuticle, which provides support and protection. The cuticle may undergo periodic shedding during growth.
  • Longitudinal Muscles: They typically have longitudinal muscles that run along the length of their bodies, enabling movement and flexibility.
  • Excretory System: Aschelminthes have a simple excretory system that helps regulate the balance of fluids and waste products in their bodies.
  • Reproduction: They reproduce through sexual or asexual means, depending on the specific species. Some species may also exhibit hermaphroditic characteristics.
  • Diverse Lifestyles: Aschelminthes include both free-living and parasitic species, demonstrating a wide range of lifestyles and ecological roles.

Phylums  : Platyhelminthes

Phylum Platyhelminthes consists of a diverse group of invertebrate animals commonly known as flatworms. These organisms exhibit a flattened, often ribbon-like body shape. Some common characteristic features of Phylum Platyhelminthes:

  • Bilateral Symmetry: Flatworms display bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis.
  • Flattened Body Shape: They have a dorsoventrally flattened body, which allows them to live in or move through narrow spaces.
  • Three Germ Layers: Platyhelminthes have three germ layers (ectoderm, mesoderm, and endoderm) during their embryonic development. These layers give rise to various tissues and organs in their bodies.
  • Digestive System: They possess a gastrovascular cavity with a single opening that serves both as a mouth and an anus. This allows them to ingest and expel food effectively.
  • Excretory System: Flatworms have a simple excretory system consisting of protonephridia, which helps regulate water balance and remove metabolic waste from their bodies.
  • Nervous System: They exhibit a ladder-like nervous system, with longitudinal nerve cords and transverse nerves that help coordinate movement and responses to stimuli.
  • Hermaphroditic Reproduction: Many flatworm species are hermaphroditic, meaning they have both male and female reproductive organs. Some species can also reproduce asexually through fission or regeneration.
  • Parasitic and Free-living Species: Platyhelminthes include both parasitic and free-living species. Some flatworms, like tapeworms, are internal parasites, while others live in freshwater or marine environments as free-living organisms.

Phylums : Ctenophora

Phylum Ctenophora, commonly known as comb jellies, comprises a group of marine invertebrates known for their comb-like rows of cilia, which they use for locomotion. They are distinct from other marine organisms due to several unique features. Some common characteristic features of Phylum Ctenophora:

  • Bioluminescence: Many ctenophores exhibit bioluminescent properties, producing light through chemical reactions within their bodies. This bioluminescence serves various purposes, including attracting prey and communication.
  • Comb Rows: Ctenophores possess eight rows of cilia, known as “combs,” that run along their bodies. These combs are responsible for their characteristic shimmering or iridescent appearance and aid in their movement through the water.
  • Biradial Symmetry: Unlike most animals, which exhibit either radial or bilateral symmetry, ctenophores have biradial symmetry. This means they have two planes of symmetry that pass through their oral-aboral axis, allowing them to be divided into two similar halves along two different planes.
  • Tentacles with Colloblasts: They have specialized tentacles that contain adhesive cells called colloblasts, which are used to capture and immobilize prey. These cells release a sticky substance to ensnare small marine organisms.
  • Gastrovascular System: Ctenophores have a simple gastrovascular system that functions in both digestion and distribution of nutrients. This system consists of a central cavity with branching canals for food digestion and transportation.
  • Diploblastic Organization: They exhibit diploblastic organization, consisting of two primary germ layers during their embryonic development. These layers include the outer ectoderm and the inner endoderm, providing the basis for the development of various tissues and organs.
  • Transparent Body: Many ctenophores have transparent or translucent bodies, allowing light to pass through them. This transparency often contributes to their delicate and graceful appearance in the water.

Phylums : Coelenterata

The term “Coelenterata” was once used to describe a now obsolete phylum that included various groups of simple, aquatic, invertebrate animals, such as jellyfish, sea anemones, and corals. However, the classification has been revised, and these organisms are now placed in separate phyla due to significant differences in their anatomical and molecular characteristics.

As of the current classification, the phylum Coelenterata is no longer recognized. Instead, the animals previously classified under Coelenterata are now typically placed in the phylum Cnidaria. Therefore, it would be more accurate to refer to this group as Cnidarians. Common characteristic features of the phylum Cnidaria (formerly Coelenterata) include:

  • Radial Symmetry: Cnidarians exhibit radial symmetry, meaning their body parts are arranged around a central axis, much like the spokes of a wheel.
  • Tentacles and Nematocysts: They have specialized tentacles armed with stinging cells called nematocysts, which they use for defence and capturing prey.
  • Gastrovascular Cavity: Cnidarians have a single body cavity called the gastrovascular cavity, which serves both digestive and circulatory purposes.
  • Two Body Forms: They typically exhibit two body forms: the polyp form, which is generally sessile and cylindrical, and the medusa form, which is typically free-swimming and umbrella-shaped.
  • Mesoglea: Cnidarians have a jelly-like, non-living substance called mesoglea located between the inner and outer layers of cells.
  • Nerve Net: They possess a simple nervous system in the form of a nerve net, which allows them to respond to stimuli in their environment.

Phylums : Porifera

Phylum Porifera refers to a diverse group of simple, multicellular animals commonly known as sponges. Sponges are primarily marine organisms, although some species can be found in freshwater environments. They are known for their unique body structure and filter-feeding capabilities. Some common characteristic features of Phylum Porifera:

  • Porous Body Structure: Sponges have a porous body structure with numerous small openings called ostia, which allow water to enter their bodies.
  • Sessile Lifestyle: They are sessile organisms, meaning they are anchored to a surface and do not move around. Sponges attach themselves to rocks, shells, or other substrates.
  • Asymmetrical or Radial Symmetry: Sponges can exhibit either asymmetrical or radial symmetry, lacking the bilateral symmetry seen in many other animals.
  • Choanocytes: They have specialized cells called choanocytes, which have a collar-like structure and flagella. Choanocytes create water currents to help the sponge filter and trap food particles.
  • Spicules and Spongin Fibers: Sponges have structural elements known as spicules, which can be composed of calcium carbonate or silica. In some sponges, a protein called spongin forms a flexible network within the body.
  • Ameboid Cells: Ameboid cells, also known as amoebocytes, are present in the mesohyl of sponges. These cells are responsible for various functions, such as digestion, transportation, and structural support.
  • Filter Feeding: Sponges are filter feeders, actively filtering water to obtain nutrients, including small particles, bacteria, and dissolved organic matter.
  • Regenerative Abilities: Sponges possess remarkable regenerative abilities, enabling them to repair and regrow damaged or removed body parts.

Phylum Porifera represents a unique and ancient lineage of animals that play a crucial role in marine ecosystems. Their simple yet specialized body structure and feeding mechanisms contribute to the overall biodiversity and ecological balance of marine environments.

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Animal Kingdom Phyla: FAQ

Q. How Many Phylum in Animal kingdom?

Ans. There were around 40 recognized phyla in the animal kingdom.

Q. Which is the Largest Phylum of Animal Kingdom?

Ans. The largest phylum in the animal kingdom is the phylum Arthropoda. Arthropods are characterized by their jointed limbs and hard external skeletons. This diverse group includes insects, arachnids, crustaceans, and myriapods, among others. They are found in a wide range of habitats and have adapted to various ecological niches, contributing significantly to the overall biodiversity of the planet.

Q. Crocodile Belongs to Which Class of Animal Kingdom?

Ans. Crocodiles belong to the class Reptilia in the animal kingdom. They are large, predatory, semiaquatic reptiles that have been around for millions of years. Along with alligators, caimans, and gharials, crocodiles are part of the order Crocodilia within the class Reptilia.

Q. What are the two main classifications of the Animal Kingdom

Ans. The two main classifications within the animal kingdom are vertebrates and invertebrates. These classifications are based on the presence or absence of a backbone.

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