Kingdom Animalia PDF

# Kingdom Animalia In the previous theme, we learnt about various kingdoms – Monera, Protista, Fungi, Plantae, and Animalia. If you observe, you would find that there is evolution of life forms. Complex multicellular organisms like birds, trees, and human beings have evolved from simple unicellular...

# Kingdom Animalia In the previous theme, we learnt about various kingdoms – Monera, Protista, Fungi, Plantae, and Animalia. If you observe, you would find that there is evolution of life forms. Complex multicellular organisms like birds, trees, and human beings have evolved from simple unicellular organisms like bacteria and amoeba. Within the plant kingdom also, we have observed how prokaryotic unicellular Monerans like bacteria evolved into eukaryotic, multicellular, saprophytic fungi and then into flower- and fruit-bearing big trees like mango. ## Invertebrates and Vertebrates Kingdom Animalia too shows an interesting evolution pattern. This kingdom is broadly classified into two divisions - Invertebrates and Vertebrates - on the basis of absence/presence of the vertebral column (backbone). Less-evolved invertebrates do not possess a vertebral column, whereas vertebrates, with the backbone, find their place high up in the evolution tree. Invertebrates comprise eight major phyla, while vertebrates are classified into five major groups. In order to observe the gradual evolutionary pattern, we will first learn about the characteristic features and see examples of different groups of invertebrates and then those of vertebrates. ## Invertebrates **(Animals without a backbone or bony skeleton)** Invertebrates are classified into eight subgroups on the basis of the level of complexity in body organization. ### 1. Porifera - Pore-bearing animals * **porus** - 'pore' + **fero** – 'bear' * These are the simplest multicellular animals with no tissues, organs, or organ systems. Their body is made up of cells that are loosely held together and perform life functions more or less independently. This is called **cellular level of organization**. * These animals do not have legs or appendages but have a **muscular foot** that helps in locomotion. * Some common examples of this group are snail, pearl oyster, and octopus. ### 8. Echinodermata - Spiny skinned animals * **ekhinos** - 'spiny' + **derma** - 'skin' * This phylum comprises very beautiful marine animals with rough, spiny, and star-like, disc-like, or flower-like bodies. * They do not have legs to move. The movement occurs with the help of **tube feet**. These tube feet also help in feeding and respiration as water moves through them. * They have a true **coelom** or body cavity with a network of fluid-filled canals that facilitate gas exchange, locomotion, and feeding. * Some common examples of this group are starfish, sea urchins, and brittle star. ## Vertebrates **(Animals with backbone or bony skeleton)** This group includes animals which are triploblastic, i.e. three layers of cells enclose the true body coelom (cavity). Vertebrates have well-developed body parts and organ systems, such as the nervous system with a well-developed brain and sense organs and two pairs of limbs or fins (in case of fishes) for locomotion. Respiration is through gills in lower vertebrates that live in water and through lungs in higher vertebrates that live on land. This group is divided into five subgroups on the basis of complexity in body organization: Pisces, Amphibia, Reptilia, Aves, and Mammals. ### 1. Pisces - Group of fishes * These are aquatic animals. * Their respiratory organs are **gills**, which help them absorb oxygen dissolved in water. ### 5. Annelida - Segmented worms * **annellus** - 'little ring', hence called ringed worms or segmented worms. * As the name suggests, the soft body of annelids is divided into segments by ring-like grooves or annuli. * They breathe through their moist body surface. * Their body wall has three layers of cells (triploblastic) and encloses a true coelom, i.e. body cavity. * They have very basic level of organ systems - nervous system and circulatory system. **Nephridia** are the special organs for excretion. * Some common examples of this group are - earthworm and leech. ### 6. Arthropoda - Animals with jointed legs * **arthron** - 'joint' + **pous** - 'foot' * As suggested by the name itself, the animals belonging to this group have jointed legs. * Their body wall has three layers of cells (i.e. triploblastic) and encloses a true coelom, i.e. body cavity. This coelom, called **haemocoel** in these animals, is reduced in size and contains blood called **haemolymph** that flows freely throughout their body, unlike us. * They have organ systems, such as the nervous system and respiratory system, which are not well developed but are in a primitive form. * Their body has three major segments - the upper part called **head**, the middle one called **thorax**, and the lower segment called **abdomen**. * This phylum comprises the largest number of organisms in the animal kingdom. Due to a huge variety in characteristic features, this phylum is subdivided into four groups: ### 3. Platyhelminthes – Flat worms * **platy** - 'flat' + **helminth** – 'worm' * These animals have a ribbon-like or leaf-like, thin, flat body without a body cavity (coelom), unlike the members of the phyla Porifera and Cnidaria. * The body wall is made up of three layers of cells, i.e. they are **triploblastic animals**. * Flatworms are mostly parasites that live inside the body - **endoparasites** of other animals or human beings which serve as **host**. Around the mouth, endoparasites have hooks, or suckers, by which they attach themselves to the host tissue. * Some examples of this group are tapeworm and liver fluke. * Like tapeworms, are the head lice and bed bugs also endoparasites? * They are **pseudo coelomate**. * Tapeworms get their name as they are long, thin, and flat like a tape. * Tapeworms can be huge! When whales get tapeworms, these on-board companions can grow to 100 feet or more! ### 4. Nemathelminthes (new name) or Aschelminthes (old name) – Threadworms or Roundworms * **nema** - 'thread' + **helminth** – 'worm' * These are small, thread-like animals with a cylindrical and unsegmented body. * These animals also have a body wall that is made up of three layers of cells, i.e. they are **triploblastic animals**. * Nematodes are found everywhere - in fresh water, sea water, or humus-rich soil. Many nematodes live as parasites and cause various diseases. * Some examples of this phylum are Ascaris, pinworm, and filarial ### 2. Coelenterata (old name) or Cnidaria (new name) - Hollow sac-like animals * **koilos** - 'hollow' + **enteron** - 'intestine' * The animals of this group have a hollow body cavity with only one opening called the **mouth**. The mouth is surrounded with finger-like structures called **tentacles**, which help the animal to catch its prey, and in locomotion. * Their body is made up of two layers of cells that surround the body cavity, i.e. they are **diploblastic animals**. They have very basic tissue-level organization. They are **Acoelomate**. * Some of these cnidarians live in groups or colonies such as corals and some cnidarians such as hydra, jellyfish, and sea anemones are solitary, i.e. live alone. ### 3. Reptilia - Group of creeping animals * They are the first vertebrates fully adapted for life on dry land. * Reptiles also are cold-blooded animals. * They lay eggs on land. * They have a partially divided four-chambered heart. * They have a dry and scaly skin. * Respiration is through lungs only. * They have two pairs of limbs to help in locomotion (except snakes). * Some examples of this group are wall lizard, crocodile, tortoise, snakes, and chameleon. ### 4. Aves - Group of birds * This group includes animals with flight adaptations such as hollow bones to keep their body light. * Body is covered with feathers and forelimbs are modified into wings. * Respiration is through lungs. * They have a completely divided four-chambered heart. * They are warm-blooded animals, i.e. they maintain a constant body temperature irrespective of the environment. * They lay eggs with hard shells. * Some examples of this group are hen, sparrow, eagle, peacock, and ostrich. ### 5. Mammalia - Group of animals having mammary glands * This group includes animals that give birth to young ones and feed them milk with the help of mammary glands. * Mammals are mostly adapted to terrestrial life, but a few like walrus and seal are semi-aquatic (not living wholly in water), and others like dolphin and whale are completely aquatic. * They are warm-blooded animals, (they maintain a constant body temperature irrespective of the environment). * Respiration is through lungs. * They have a completely divided four-chambered heart. * Their body is covered with hair or fur. * They have two pairs of limbs. * Some examples of mammals are rat, kangaroo, lion, deer, and human beings.