Kingdom Animalia – Different Phylum, Classification, Characteristics

Kingdom Animalia is the largest phylum of animals, containing all animals that are known to scientists at the present time.

Kingdom Animalia - Different Phylum, Classification, Characteristics

Having a solid understanding of Kingdom Animalia is integral to understanding the makeup of our world, as well as the creatures inhabiting it, but the sheer volume of information can make this a little overwhelming.

To help, we have put together everything that you need to know about Kingdom Animalia, including the key terms, the animals included, and the information that you need to know.

What Is Kingdom Animalia?

The Kingdom Animalia contains all animals that are known by science today (as opposed to plants).

It includes all invertebrates such as insects, arachnids, mollusks, annelids, echinoderms, flatworms, jellyfish, etc., as well as vertebrates like fish, amphibians, reptiles, birds, and mammals. 

The Kingdom Animalia also includes some other groups that aren’t strictly animals, such as sponges, placozoans, ctenophores, and porifera.

Key Terms

In order to properly understand Kingdom Animalia, it is important to have a solid understanding of the key terms that tend to be used in discussions on these topics, and we will take a closer look at some of the most common and important terms below, along with clear, simple definitions.

  • Animalia: A group of organisms with common features. In this case, Animalia refers to all living things that share a common ancestor.
  • Invertebrate: An organism without a backbone or spinal column. This means they don’t have a skull, neck, or spine. They include insects, spiders, mollusks (like snails), and sea anemones.
  • Vertebrate: Any animal with backbones, which includes fish, amphibians, birds, reptiles, and mammals.
  • Arthropoda: All animals with jointed limbs, including crabs, lobsters, shrimp, ticks, millipedes, centipedes, scorpions, spiders, mites, and bees.
  • Mammalia: Animals with hair, fur, hooves, claws, wings, mammary glands, and milk-producing tears. Humans are mammals.
  • Amphibian: An aquatic animal with two sets of gills on its back, webbed feet, and a tail fin. Frogs, salamanders, newts, caecilians, and frogs are examples of amphibians.
  • Reptile: An animal with four legs and scales covering its body. Snakes, lizards, turtles, crocodiles, tortoises, and iguanas are reptiles.
  • Bird: An air-breathing, warm-blooded animal with feathers, beaks, and wings. Birds include ducks, geese, swans, ostriches, penguins, parrots, owls, falcons, hummingbirds, and eagles.
  • Fish: An aquatic animal with fins, scales, and a tail. Sharks, rays, cat sharks, cod, salmon, trout, pike, tuna, bass, carp, goldfish, and guppies are just a few examples of fish.
  • Fungi: Organisms that produce spores and reproduce through budding. Fungi include mushrooms, truffles, rusts, mildews, smuts, and yeasts.
  • Plantae: Plants are green, photosynthetic organisms that lack any specialized organs for locomotion.

They include ferns, mosses, algae, conifers, cycads, palms, gymnosperms, and angiosperms.

  • Placozoa: Placozoa are single celled creatures that live in water and feed off bacteria. They are sometimes called “sea eggs.”
  • Sponge: Sponge is another name for Porifera, which is a phylum that includes sponges, corals, and sea squirts.
  • Ctenophora: Ctenophora are marine animals that resemble comb jellies. They include comb jellies, tubeworms, and squid.
  • Porifera: Porifera are soft-bodied animals that lack true muscles or bones. They include sponges, corallines, sea pens, sea cucumbers, and jellyfish.
  • Chordata: Chordates are animals with a notochord, meaning their bodies consist of a long string of cells running from head to tail.

They include humans, fish, sharks, dolphins, whales, lampreys, hagfish, and tunicates.

  • Echinodermata: Echinoderms are a phylum consisting of starfish, sea urchins, brittle stars, sand dollars, sea cucumbers, sea lilies, sea dragons, sea angels and sea biscuits

1. Chordate phylum: The Chordate phylum includes humans, fishes, amphibians, reptiles, birds, bats, and other vertebrate animals.

2. Arthropoda phylum: This phylum includes arachnids, crabs, insects, spiders, centipedes, millipedes, scorpions, mites, ticks, and horseshoe crabs.

3. Mollusca phylum: This phylum includes bivalves, gastropods, cone shells, chitons, whelks, limpets, tusk shells, and some cephalopods (octopus, squid).

4. Echinodermata: This phylum includes starfish, sea urchins and sea cucumbers  as well as brittle stars, and sea lilies.

5. Nemathelminthes: This phylum includes roundworms, ribbon worms and flatworms.

6. Annelida: This phylum includes earthworms, leeches, slugs, pill bugs, and segmented worms.

7. Brachiopoda: This phylum includes brachiops and brachiopods such as clams, oysters and snails.

8. Bryozoa: This phylum includes coral, sponge, and sea anemone.

9. Platyhelminthes: This class includes flukes, tapeworms, and nematodes.

Kingdom Animalia: A History

Kingdom Animalia: A History

The idea of the Kingdom Animalia first arose in the late 18th century, when Carl Linnaeus was studying the animal world.

He noticed that there were many similarities between plants and animals. He divided all living things into two groups: Plantae and Animalia. 

Later on, he added another group to his classification system called Protista which included protozoans, fungi, algae and slime molds.

Animalia is one of the three kingdoms of life. It consists of all multicellular organisms including plants, fungi, protists, bacteria, and metazoan animals.

Animalia are also known as Metazoa or Multicellular Animals.

They are differentiated from plants because they possess specialized cells called somatic cells that perform specific functions.

These cells can be either reproductive cells (reproductive cells) or non-reproductive cells.

Non-reproductive cells include nerve cells, muscle cells, epithelial cells, connective tissue cells, blood cells, bone cells, etc.

Reproductive cells include spermatozoa, ova, ovaries, testes, eggs, and sperms.

There are about 1.9 million species of animals on Earth today. Of these, only around 10% are classified as having true sexual reproduction.

Most of the remaining 90% reproduce asexually through mitosis. Some of them may even reproduce both sexually and asexually.

What Are Phylums?

We have briefly mentioned the significance of Phylum in our list of key terms above, but just what do we mean by this?

Well, let us take a look at the different types of phylum and their characteristics.

Phyla are subdivisions of the Animalia kingdom based on shared traits. There are 9 phyla currently recognized.

Each phylum contains a unique set of body structures and cell types.

1. Chordata: The chordates are characterized by the presence of notochords. Notochords are elongated, rod-like structures present in early embryos.

They play a major role in embryonic development.

2. Arthropoda: The arthropods are characterized by jointed appendages. Joints are parts of the skeleton where articulations occur.

In humans, joints allow for movement while providing protection against injury.

3. Cnidaria: The cnidarians are characterized by stinging tentacles. Stinging tentacles are used for defense and feeding.

4. Porifera: The poriferans are characterized by spicules. Spicules are rigid rods found in the walls of some marine invertebrates.

5. Nematoda: The nematodes are characterized by having no mouth. They feed using a stylet which is a long, thin tube with teeth along its length.

6. Platyhelminthes: The platyhelminthes are characterized by having an unsegmented body. Segments are segments of the body that form during embryogenesis.

7. Echinodermata: The echinoderms are characterized by five pairs of ambulacral plates. Ambulacral plates are small, plate-like structures located under the arms of the animal.

8. Annelida: The annelids are characterized by having segmental bodies. A segmental body is a series of repeating units called rings.

Rings are made up of repeated segments.

9. Mollusca: The molluscs are characterized by having two shells. Shells are hardened portions of the body that protect the soft tissues inside.

The Phylum classification system is quite simple. It basically divides all living things into groups based on how similar they are to each other.

This helps us understand the relationships between organisms better. 

For example, if you were to compare human beings to chimpanzees, then you would say that humans are more closely related to chimps than they are to dogs or cats.


The first phyla in the animal kingdom is known as Chordata, meaning ‘string’.

This group includes vertebrates (animals with backbones), tunicates (sea squirts), and urochordates (sea cucumbers).

All of these share certain features such as a notochord, a dorsal nerve cord, and gills.

Chordate Features

  • All Chordates will have a vertebrate backbone, and this means that there is a spine running down the center of the back of the animal. These animals also have paired fins on their tails.
  • All Chordates have gills. Gills are organs that help filter water through the skin.
  • All Chordates possess a notochord. This is a flexible structure that runs down the middle of the spinal column. Notochords provide support to the embryo and aid in locomotion.
  • All Chordates contain a dorsal nerve cord. Dorsal nerve cords are bundles of nerves that run from head to tail. They act as communication systems among cells within the body.
  • All Chordates have a skeleton, but it is very different from that of other phyla. Instead of being composed of bone, their skeletons are made of cartilage.

Cartilage is a type of connective tissue that allows bones to move freely.

  • All Chordates do not have mouths. Instead, they use tentacles to take food into their bodies. Their digestive tract is also completely separate from their mouth.

Chordate Classification

Classification of chordates is fairly easy. There are three main classes of chordates: Cephalochordates, Tunicata, and Urochordates.

Cephalopods are members of the phylum Chordata. They are divided into two subphyla; Cephalochordata and Craniata. Cephalopods include squid, octopus, cuttlefish, and nautilus.

The tunicate is an invertebrate that has a sac-like body covered in a thin layer of epithelial cells. This sac is called the tunic.

Some species of tunicates are jellyfish. Urochordates are marine invertebrates that look like sea cucumbers. They are sometimes referred to as “tunicates”.



Arthropod means ‘jointed foot’ because arthropods have jointed appendages.

Arthropods are one of the most diverse phyla of animals. Most insects belong to this phylum.


Insects are an extremely diverse class of animals. They can be found almost everywhere on Earth, including Antarctica. Many insects live in symbiotic relationships with plants.

Others eat plant material, while still others feed on meat. Insects are often considered pests, but many people find them fascinating.

There are about 1 million described insect species.

There are four major groups of insects:

  • Coleoptera: The order Coleoptera contains beetles. Beetles are important agricultural pests. For example, the Colorado potato beetle causes serious damage to potatoes.
  • Lepidoptera: The order Lepidoptera includes butterflies and moths. 

As you may know, butterflies are commonly seen in gardens, and enjoy flowers and leaves, while moths are nocturnal creatures that fly around at night looking for places to lay eggs.

  • Hymenoptera: The order Hymenoptera includes bees and wasps, both of which are social insects, as well as ants, which are more solitary, and sawflies, which are parasitoids. 
  • Diptera: The order Diptera includes flies (or true bugs). Flies are common throughout the world, and some are even beneficial. However, there are also many types of disease-transmitting flies.

Arthropoda Features

Some of the main distinctive features of Arthropoda include:

  • Joints: Arthropods have joints. These are small areas where two or more parts of the body meet.

Joints allow movement and flexibility. In addition, they help protect the animal’s internal organs.

  • Skeleton: Arthropods have a hard exoskeleton. This protects the soft tissues inside the body. It also helps keep the creature warm.
  • Mouth: Arthropods have external openings called mouthparts. These are used to ingest food.
  • Digestion: Arthropods digest their food internally. They do not need to chew it before swallowing.

Instead, they break down the food by using enzymes produced in their stomachs.

  • Circulatory System: Arthropods have circulatory systems. Blood flows through these systems. Red blood cells carry oxygen from the lungs to all parts of the body.
  • Respiratory system: Arthropods breathe air. Their respiratory systems consist of tracheae, which connect to spiracles.

Spiracles are holes located near the surface of the skin. Air enters the tracheae, then passes into the spiracle. From there, it moves into the rest of the body.

  • Sense Organs: Arthropods have sense organs. These organs detect light, sound, smell, taste, temperature, pressure, pain, and other things.

Some insects have eyes, antennae, and legs. Other animals have only eyes or antennae.

  • Reproduction: Arthropods reproduce sexually. Males and females mate. Then, fertilized eggs develop into larvae, pupae, or adults.
  • Development: Arthropod development is very different from human development. Larvae hatch out of the egg and grow into adult forms.
  • Metamorphosis: Arthropods undergo metamorphosis. During this process, individuals change form. For instance, caterpillars turn into butterflies.
  • Reproductive cycle: Arthropods have one reproductive cycle. Females produce eggs. Eggs become larvae, pupae, and eventually adults.
  • Habitat: Arthropods live on land, in water, or in the air. Many species live underground. Others live in trees, under rocks, and in burrows. Some arthropods live in caves.
  • Food: Arthropods eat plants, fungi, bacteria, protozoa, nematodes, mollusks, and other invertebrates. Some feed on dead animals.

Arthropoda Classification

There are three major groups of arthropods: Insecta, Crustacea, and Chelicerata. Insecta includes most of the familiar insects such as bees, ants, beetles, wasps, and cockroaches.

Crustacea includes crabs, lobsters, shrimp, barnacles, and krill. Chelicerata includes spiders, scorpions, ticks, and horseshoe crabs.

Class Insecta

The Insecta class contains many familiar insect orders, including Diptera (flies), Lepidoptera (butterflies and moths), Coleoptera (beetles), Hymenoptera (bees, sawflies, and ants), Orthoptera (grasshoppers and crickets), Hemiptera (true bugs), Psocodea (cicadas), and Neuroptera (lacewings).

Order Diptera

There are about 20,000 known species of dipterans. Most of them bite with piercing mouthparts called proboscis.

Biting flies include mosquitoes, midges, gnats, black flies, and horseflies. Short-bodied flies include houseflies, blowflies, flesh flies, robber flies, and crane flies. 

The order Diptera contains two suborders: Nematocera (biting flies) which contains four families (anoplura, culicidae, muscidae and simuliidae), and Brachycera (short-bodied flies) which refers to short-bodied flies.

These include the true bugs, caddisfly, mayfly, stonefly, dragonfly, damselfly, and butterfly families.

Order Lepidoptera

The lepidopteran insect order is the largest group of living insects. It has over 100,000 described species.

The order Lepidoptera consists of five superfamilies: Papilionoidea (including butterflies, skippers, and moths), Gelechioidea, Hesperioidea, Pyraloidea, and Drepanoidoidea.

Order Coleoptera 

The coleopteran insect order is one of the oldest orders of animals. It contains beetles, weevils, ground beetles, rove beetles, booklice, and others.

The order Coleoptera also includes many important agricultural pests including corn rootworms, Colorado potato beetle, boll weevil, and European corn borers.

Order Hymenoptera

Hymenoptera is a large order of insects with about 20,000 described species. Most hymenopterans have a single pair of wings but some groups have multiple pairs.

The order Hymenoptera is divided into four suborders: Apocrita, Symphyta, Diplura, and Aculeata.

Order Orthoptera

Orthoptera is an order of insects that includes grasshoppers, crickets, katydids, and tree frogs. The order Orthoptera is divided into suborders:

  • Suborder Ensifera: The suborder ensifera (en in; fer iron) contains the true grasshoppers, tree crickets, and katydids.
  • Suborder Strepsiptera: The strepsiptera suborder is composed of two families: Gryllacrididae and Tettigoniidae.
Order Hemiptera

The hemipteran insect order is made up of two suborders: Sternorrhyncha (true bugs) and Nepomorpha (water striders).

True bugs include stink bugs, assassin bugs, shield bugs, water boatmen, aphids, scale insects, mealybugs, whiteflies, psyllids, and planthoppers.

Water striders include nymphs of the family Gerridae.

Order Psocodea

Psocodea is the name given to a group of arthropods that lack jointed legs.

These include horseshoe crabs, scorpions, spiders, centipedes, millipedes, pseudoscorpions, and pycnogonida.

The order Psocodea is divided into three superfamilies: Pycnogonida, Scorpionoidea, and Crustacea.

  • Pycnogonida: This superfamily is made up of the pycnogonids or sea louse. Pycnogonids are marine crustaceans found worldwide.
  • Scorpionoidea: The scorpionidae superfamily includes the scorpions, mites, solifugae, and kin.
  • Crustacea: The crustaceans are the largest animal phylum on Earth. They include lobsters, shrimp, crabs, barnacles, and amphipods.
Order Neuroptera

Arachnids or Araneae, also called spiders, are members of the class Arachnida.

They are generally considered as being the most primitive living member of the arthropod lineage.

Some arachnids are venomous, others are not. The order Neuroptera is divided into five suborders:

  • Subdivision Aethiopica: Includes the aethiopian whip scorpion, the aethiopian stick insect, the aethiopica tarantula hawk, and the ethiopian wolf spider.
  • Subdivision Amblypygi: Includes the amblypygi wasps, the amblypygids, and the amblypygi from flies.
  • Subdivision Anoplura: Includes the parasitic hymenoptera, the parasitic dipterans, and the parasitic coleopterans.
  • Subdivision Chelicerata: Includes the chelicerates, the mygalomorphs, and the anomalocaridids.
  • Subdivision Cyclorrhapha: Includes the cyclorrhaphan fly, the cyclorrhapha beetles, the cyclorrhapha midges, the cyclorraphoids, and the cyclorrhapha butterflies.
Class Crustacea

The crustacean subphyla are Decapoda (shrimp), Brachyura (crabs), Penaeidae (penaeus shrimps), Amphipoda (amphipods), Isopoda (pill bugs), Siphonostomatoida (barnacles), Malacostraca (lobster, prawns, etc.), Maxillopoda (maxillary appendages), Branchiopoda (brine shrimp), Copepoda (crawfish), Ostracoda (cockroaches), Oniscidea (woodlice), and Trichoptera (caddisfly larvae).

Class Chelicerata

Chelicerata is a large taxonomic order which includes spiders, ticks, mites, harvestmen, scorpions, and their relatives.

It is one of the oldest extant orders of animals, dating back at least 300 million years. 

Most species have eight legs and an exoskeleton covered in hairs, bristles, spines, or other structures.

Their mouthparts consist of four pairs of mandibles, each pair with its own set of teeth for chewing food. Many chelicerate species can move by means of jumping or running.



The third phyla is known as Cnidaria, which contains jellyfish, corals, sea anemones, sea pens, hydrozoans, and hydromedusae.

Cnidaria Examples

Some of the main types of Cnidaria include:


Jellyfish are eumetazoa cnidarians that live in oceans around the world. There are over 10,000 different types of jellyfish.

They are usually transparent, but some species may be translucent or even opaque.

Jellyfish do not have any bones, so they cannot crawl away from predators. Instead, they use tentacles to capture prey.


A coral reef is a community of marine organisms, including plants, algae, invertebrates, and fish, that grow together in an environment supplied with sunlight and nutrients.

Coral reefs provide habitat for many species of fish, sea turtles, birds, mammals, and other animals. Coral reefs are found in tropical waters worldwide.

Sea Anemone

A sea anemone is a small animal that has a soft body and no hard parts. The most common type of sea anemone is the tube-dwelling anemone.

Tube-dwelling anemones are usually attached to rocks or shells with a long stinging column called a nematocyst. This nematocyst is used to inject venom into passing creatures.


Hydrozoans are aquatic animals that lack true tissues, such as muscles, nerves, and blood vessels.

Because of this, they rely on water currents to circulate fluids throughout their bodies. Some species of hydrozoans are filter feeders, while others are carnivores.


Hydromedusae are also known as sea whips. These are tiny marine animals that swim using whip-like tails. They are often brightly colored.

Sea Pens

Sea pens are colonies of polyp-bearing sessile benthic suspension feeders. They are sometimes referred to as “sea fans” or “sea lilies”.

Sea pens are typically colonial organisms, although solitary individuals are known. Sea pens are commonly found in coastal areas where there is strong tidal current.

Cnidaria Features

Some of the main features of cnidaria include:

  • All cnidarian cells contain nuclei.
  • Cnidarian cells do not have cell walls.
  • A single layer of epithelial cells lines the entire surface of the organism.
  • Each individual cell is surrounded by a fluid-filled cavity called a coelom.
  • Cells communicate through chemical signals.
  • Cnidarians reproduce sexually.
  • Cnidarians have two sexes.
  • Cnidarians lack vertebrae.
  • Cnidarians possess a nervous system.
  • Cnidarians do not have a circulatory system.
  • Cnidarians’ digestive systems are simple.
  • Cnidarians absorb food via a pharynx.
  • Cnidarians excrete mucus.
  • Cnidarians have a specialized organelle called a tentacle.
  • Cnidarians have tentacles, made up of multiple segments.
  • Cnidarians have a mouth at the anterior end of the body.
  • Cnidarian tentacles are covered with sensory hairs called setae.

Cnidaria Classification

There are more than 10,000 different kinds of Cnidaria. All belong to one of three phyla: Anthozoa (corals), Hydrozoa (hydromedusae) and Scyphozoa (jellyfish).

Anthozoans are divided into four classes: Actiniaria, Cubozoa, Medusozoa, and Octocorallia.

  • Actiniaria includes the following orders: Alcyonacea, Antipatharia, Coralliophila, Dendro Nereida, Euphyllia, Lithophyllida, Merulinidae, Millepadaliina, Nassariidae, Pectinariidae, Scleractinia, Tubastraea, Turbinidae, Verongida, Zoanthidea.
  • Cubozoa include the following order: Calcispongiae.
  • Medusozoa include the following orders: Acropora, Ceriantharia, Chlor Acantharia, Comatulida, Coscinodiscus, Cyanea, Diploastrea, Dysidea, Gorgonocephalidae, Heterostelechidae, Leptotheca, Lobo Phylliidae, Microcosmus, Montipora, Mycedium, Nausithoe, Oculinella, Paragorgia, Porites, Psammaplexus, Raccolta, Rhombopora, Sphenobaena, Stylaster, Tabulata, Thalassiosira, Trachymedusae, Trichocysts, Urogymnura, Xenia, Xestospongia.


Another category of phyla are porifera, which means “porous”, referring to the fact that these animals have no skeleton.

The word “sponge” comes from the Greek word spongos meaning sponge.

Porifera are usually soft bodied invertebrates that live attached to a substrate such as rock, coral reef, sea floor, etc., using a variety of methods including cementing themselves together with their own secretions, attaching themselves to other creatures, or living on algae. 

Porifera can be classified into five groups: Demosponges, Hexactines, Homosiphonia, Poecilosclerida, and Tetractinellida.

  • Demosponges are the most diverse group of sponges. There are about 6,500 species in this group.

They are characterized by having a network of fibers that form an open structure. Most demosponges feed by filtering water drawn through the pores of the sponge. 

Some demosponges use their bodies as filters; others filter particles out of seawater. Many species of demosponges also produce chemicals that kill bacteria and parasites.

  • Hexactines are small marine sponges found in shallow waters all over the world. Their skeletons consist of hexagonal plates connected by thin rods.

These sponges are often brightly colored. 

For example, some species of Hexactinellida are red, orange, yellow, green, blue, purple, pink, white, black, and brown.

  • Homophobia is another group of marine sponges. It has been suggested that they may be related to the Hexactinellida.
  • Poecilosclerida sponges are one of the largest groups of sponges.

They grow up to across and are commonly known as Sea Sponge because they are so common in tropical seas. They are sometimes called “sea apples”. 

The name poecilosclerida refers to the similarity between the shape of the body and the head of a fish.Tetractinellida is a group of very rare sponges. They are mostly found in deep-water environments.

Porifera Characteristics

Some of the main characteristics of porifera include:

  • They have a hard outer layer (the exoskeleton) and a softer inner part (the endoskeleton).
  • The exoskeletons of many sponges are made of calcium carbonate, but there are also sponges whose skeletons are made of silica, chitin, cellulose, magnesium phosphate, iron oxide and other materials
  • Sponges are not plants nor animals, but rather a type of multicellular organism.
  • Sponges do not have blood vessels, nerves, bones, muscles, or any other sort of internal organs. However, they do have cells that perform functions similar to those of other organisms. In addition, they have cell types that are unique to them.
  • Sponges can survive without food for long periods of time.
  • Sponges are usually soft and flexible.
  • Sponges reproduce both sexually and asexually.
  • Sponges live in almost every environment on Earth.

Porifera Classification 

Sponges are classified into two major phyla: Porifera and Demospongiae.

There are several subphyla within these phyla, and these include: Calcarea, Clionaida, Dictyoceratida, Dysidea, Halichondrida, Heteroxyidae, Spongillidae, Leucosolenia, Microciona, Myxillina, Osculatiidae, Petrosida, Placodermi, Polymastia, Pourtalesiidae, Spirocystina, Tetraclitacea, Thorectidae, Trachymedusae, Verongimorpha, Xenastra, Xesto Idea, Zoantharia, and others.


The nematodes are characterized by having no mouth. They feed using a stylet which is a long, thin tube with teeth along its length.

Their bodies are elongated and wormlike. Nematodes are divided into three classes: Chromadorea, Enoplea, and Spirurida.

Nematoda Characteristics

The primary characteristic of nematoda is their lack of mouth.

Nematoda Classification

Nematodes are classified into three classes: Chromadoria, Enoplia, and Spirurida. These are further subdivided into various orders, families, genera, and species.


The chromadorea nematode has an anterior region that contains the esophagus and pharynx. It has a posterior region that contains the intestine and rectum.

This class includes the following orders: Ascaridoidea, Diplogasteromorpha, Rhabditoidea, Strongyloid Idea, Travassuloidea, and Trichocephalida.


The enoplian nematode has a single-chambered esophagus and lacks a buccal cavity. This class includes the order Enoplea.


The spirurida nematode has a large buccal cavity and four chambered stomachs.

This class includes the orders Aphelenchoididae, Capillariidae, Cyathostominae, Gongylonema Today, Haemonchus, Longistriatidae, Oxyuroidea, Physalopteridae, Rhabdoderma Today, Otariidae, Stephano Filariidae, Strongyloidiasis, Triodontophorus, and Ucinetid.



Platyhelminthes are flatworm-type animals that have a body covered by a cuticle.

The Platyhelminthes are divided into six classes: Acoela, Cephalochordata, Cycliophora, Gastrotricha, Monogenea, and Trematoda.

Platyhelminthes Characteristics

Platyhelminthes are characterized by the following features:

  • A coelomic system consisting of a gut and associated organs (glandular tissue)
  • A muscular layer surrounding the entire body
  • A simple nerve net that connects all parts of the body
  • A pair of tentacle-bearing lateral appendages called cirri


Echinoderms are marine invertebrates belonging to the phylum Echinodermata.

In general, echinoderms are characterized by five pairs of ambulatory arms or fins, one dorsal and four ventral. 

They also possess radial symmetry in the arrangement of the body segments.

The echinoderms are divided into eight classes: Asteroidea, Crinoidea, Holothuroidea, Ophiuroidea, Paxillosida, Pedinoida, Solenogastres, and Vestimentifera.

Echinoderms Characteristics

  • A central nervous system with a brain and spinal cord
  • An endoskeleton composed of mineralized plates
  • Five pairs of ambulatory limbs
  • A radial symmetry in the arrangement and number of body segments
  • A radially symmetric organization of the internal organs


Annelids are segmented worms with a head at each end. They are typically soft bodied, but some groups such as earthworms have hard exteriors.

Annelids are divided into two subphyla: Polychaeta and Hirudinea.

Annelida characteristics include the following:

  • Body is unsegmented, lacking true segments
  • Head at both ends
  • No anus
  • Mouth on underside
  • Two rows of parapodia
  • Parapodia usually bear hooks
  • Spiracles present in most polychaete species
  • Tubules present in many species


Mollusks are members of the phylum Mollusca. Mollusks have a mantle covering their bodies.

Most mollusks are bivalves; however, there are other types of mollusks including gastropods, cephalopods, tectibranchiates, monoplacophorans, and brachiopods.

There are three major divisions within the Mollusca: Bivalvia, Gastropoda, and Cephalopoda.

Molluscan characteristics include the following:

  • Bivalve shell consists of two shells joined together along an edge
  • Gastropod shell is formed from a single piece of calcite
  • Cephalopod shell is made up of a series of chambers separated by a thin partition
  • The mantle covers the whole body except for the tentacles and mouth

Final Thoughts

There you have it!

This is just a brief introduction to the different segments of the Kingdom Animalia – this is just a brief overview of the phyla involved, as this is a broad topic with plenty to learn!

Jennifer Dawkins