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Ans. Animalia, also known as the animal kingdom, is a classification that includes multicellular, eukaryotic organisms that are typically motile, rely on other organisms for food (heterotrophic), and reproduce sexually. It includes a wide range of life forms, from simple invertebrates to complex vertebrates like mammals, birds, and reptiles.
Q. What are 5 characteristics of Animalia?
Ans. The kingdom Animalia is characterized by multicellularity, eukaryotic cell structure, heterotrophic nutrition, mobility, and sexual reproduction. Animals are composed of multiple cells, their cells contain a nucleus, they obtain food by consuming other organisms, most can move at some life stage, and the majority reproduce sexually through the fusion of male and female gametes.
Q. What are the 9 types of phylum?
Ans. The nine major phyla in the kingdom Animalia include Porifera (sponges), Cnidaria (jellyfish, corals), Platyhelminthes (flatworms), Nematoda (roundworms), Annelida (segmented worms), Arthropoda (insects, spiders, crustaceans), Mollusca (snails, clams, squids), Echinodermata (sea stars, sea urchins), and Chordata (vertebrates like mammals, birds, and fish).
Q. How many animals are in Animalia?
Ans. The kingdom Animalia includes around 8.7 million known species, with many more still undiscovered. This vast diversity ranges from microscopic organisms to large mammals.
Q. Which is the largest phylum in Animalia?
Ans. Arthropoda is the largest phylum in the kingdom Animalia, encompassing over a million described species. This phylum includes an extensive range of organisms such as insects, arachnids, and crustaceans, found in nearly every habitat on Earth.
Animalia, Definition, Classification of Animalia, and Importance
Animalia, This article provides a detailed overview of Animalia, including its definition, classification, and importance, as well as related MCQs with answers.
Krati Saraswat4 Jun, 2025
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The Animalia kingdom, also known as the animal kingdom, includes a wide variety of living organisms that share certain common characteristics. All members of Animalia are multicellular and eukaryotic, meaning their cells have a nucleus. They are heterotrophic, which means they cannot make their food and must consume other organisms. Understanding Animalia is essential for the NEET Exam as it covers fundamental aspects of biological diversity and evolution.
Definition of Animalia
The Animalia kingdom encompasses multicellular, eukaryotic organisms that primarily consume organic material. Animals are characterized by their ability to move at some point in life, heterotrophic nutrition, and complex cellular organization. They exist in various environments, including terrestrial, aquatic, and aerial habitats.
Animals in the Animalia kingdom are classified based on different characteristics, such as body structure, type of body symmetry, and layers of tissue.
Basis of Classification: Classification is based on traits like cell arrangement, presence of tissues, and organ systems.
Levels of Organization : Animals show different organizational levels, such as cellular (basic), tissue (organized cells), organ (organized tissues), and organ systems.
Body Symmetry : Animals exhibit symmetry, either radial (like in starfish) or bilateral (like in humans).
Germ Layers: Germ layers develop into different body parts. Animals can have two layers (diploblastic) or three layers (triploblastic).
Coelom (Body Cavity): The coelom is a cavity between the digestive tract and body wall, providing space for organs.
Segmentation: Some animals, like earthworms, have a segmented body for movement and development.
Phylum of Kingdom Animalia
The kingdom Animalia is divided into various phyla based on body structures, features, and complexity.
Porifera (Sponges)
Members of porifera phylum are commonly known as sponges, and they are predominantly found in marine environments. Most sponges are asymmetrical, primitive multicellular animals with a cellular level of organization. They possess a unique canal system for water circulation, which flows through pores (ostia) in the body wall into a central cavity (spongocoel) and exits through the osculum. This system aids in food collection, respiration, and waste removal. Sponges have specialized cells called choanocytes (collar cells) that line the spongocoel, facilitating digestion internally. Their skeleton is made of spicules or spongin fibers. As hermaphrodites, they produce both eggs and sperm. They reproduce asexually through fragmentation or sexually by producing gametes, with fertilization occurring internally. Their development includes a larval stage distinct from adults. Examples : Sycon (Scypha), Spongilla (Freshwater sponge), Euspongia (Bath sponge).
Coelenterata (Cnidaria)
Cnidarians are aquatic animals, mainly marine, and display radial symmetry. They are named after their stinging cells, called cnidoblasts, located on the tentacles. These cells are essential for capturing prey and provide defense. Coelenterates exhibit a tissue level of organization and are diploblastic, having an external gastrovascular cavity with a single mouth. They possess a skeletal structure made of calcium carbonate in certain species, such as corals. The two main body forms in this phylum are the polyp (sessile, cylindrical) and medusa (umbrella-shaped, free-swimming). Species that exhibit both forms alternate generations through a process called metagenesis. Examples : Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan), Meandrina (Brain coral).
Ctenophora (Comb Jellies)
Also known as comb jellies or sea walnuts, these exclusively marine organisms are radially symmetrical, diploblastic, and exhibit tissue-level organization. They are recognized by their rows of ciliated comb plates, which assist in locomotion. Ctenophores can emit light, a property known as bioluminescence. They are hermaphroditic and reproduce sexually, with external fertilization and indirect development. Examples : Pleurobrachia, Ctenoplana.
Platyhelminthes (Flatworms)
Flatworms are named for their flattened, leaf-like bodies and are primarily parasitic. They display bilateral symmetry, are triploblastic, and lack a body cavity (acoelomate). Organ level of organization is present. Special adaptations like hooks and suckers enable them to latch onto hosts, and their cells called flame cells help in excretion. These organisms are hermaphroditic, with internal fertilization and multiple larval stages in development. Many, like Planaria, have remarkable regeneration abilities. Examples : Taenia (Tapeworm), Fasciola (Liver fluke).
Aschelminthes (Nematodes or Roundworms)
Aschelminthes are found in varied environments and may be parasitic or free-living. These organisms are bilaterally symmetrical, triploblastic, and have a pseudocoelom (a partially lined body cavity). The body is cylindrical, and they possess a complete digestive system and a muscular pharynx. They are dioecious, meaning sexes are separate. They may have direct development, where the young resemble the adult, or indirect development with a distinct larval stage. Examples: Ascaris (Roundworm), Wuchereria (Filaria worm), Ancylostoma (Hookworm).
Annelida (Segmented Worms)
Annelids are found in aquatic and terrestrial habitats and exhibit bilateral symmetry with a segmented body. The segments allow for flexibility and efficient movement, aided by circular and longitudinal muscles. Aquatic species, like Nereis, use parapodia (small appendages) for swimming. These organisms possess a closed circulatory system, with specialized structures called nephridia for excretion. The nervous system consists of paired ganglia connected by a ventral nerve cord. Examples: Nereis, Pheretima (Earthworm), Hirudinaria (Leech).
Arthropoda (Insects and Allies)
The largest phylum in Animalia, Arthropoda , encompasses a wide range of insects and other organisms. These animals have a segmented body, jointed appendages, and a chitinous exoskeleton. They exhibit bilateral symmetry and organ-system level organization. Arthropods have an open circulatory system and diverse respiratory organs, including gills, lungs, and tracheae. Sensory organs such as antennae and compound eyes are well-developed. Examples: Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect), Anopheles (Mosquito), Limulus (King crab).
Mollusca (Soft-bodied Animals)
Mollusks are the second-largest phylum, consisting of soft-bodied animals with a calcareous shell, a muscular foot, and a distinct head region. They are mostly aquatic but can also be found on land. The space between the visceral hump and the mantle forms the mantle cavity, housing feather-like gills for respiration. They are dioecious and reproduce via indirect development.
Echinoderms , exclusively marine, are known for their calcareous endoskeleton, which gives them their spiny appearance. Adults show radial symmetry, but their larvae are bilaterally symmetrical. Echinoderms possess a unique water vascular system that assists in locomotion, food capture, and respiration. They have an indirect development stage with free-swimming larvae. Examples : Asterias (Starfish), Echinus (Sea urchin).
Hemichordata (Acorn Worms)
Initially categorized under Chordata, Hemichordata now stands as a separate phylum. These worm-like marine organisms have a proboscis, collar, and trunk structure. They exhibit bilateral symmetry and an open circulatory system, with gills for respiration and proboscis glands for excretion. They are dioecious, with external fertilization and indirect development. Examples : Balanoglossus, Saccoglossus.
Chordata (Animals with Notochord)
Chordates are defined by having a notochord, a dorsal hollow nerve cord, and pharyngeal gill slits. They possess a post-anal tail and a closed circulatory system. Chordates display a high level of organ-system organization and are further classified into subgroups based on additional structures, including vertebrates with a developed spinal column.
Examples: Mammals, birds, fishes, reptiles, and amphibians.
Subphyla of Phylum Chordata
Chordata is divided into three subphyla:
Urochordata (Tunicata): These are exclusively marine animals in which the notochord is only present in the larval tail. Common examples include Ascidia, Salpa, and Doliolum.
Cephalochordata: Also marine, members of this subphylum have a notochord that extends from the head to the tail and remains throughout their life. An example of cephalochordates is Branchiostoma (also known as Amphioxus or Lancelet).
Vertebrata : Vertebrates possess a notochord during the embryonic stage, which is later replaced by a vertebral column made of cartilage or bone in adults. Vertebrates exhibit additional distinct characteristics, such as a muscular heart (with two, three, or four chambers), kidneys for excretion and osmoregulation, and paired appendages, which can be fins or limbs.
Importance of Animalia
The kingdom Animalia plays a crucial role in various ecosystems and offers significant benefits to humans and the environment. Here are some key points highlighting the importance of Animalia:
Ecosystem Balance : Animals contribute to maintaining ecological balance by serving various roles, such as predators, prey, pollinators, and decomposers. They help regulate populations of other species, promoting biodiversity and stability within ecosystems.
Food Chain Dynamics : Animals are integral components of food webs and chains, where they serve as both producers and consumers. Herbivores, carnivores, and omnivores interact with plants and other organisms, supporting energy flow and nutrient cycling.
Pollination : Many animals, particularly insects like bees, butterflies, and birds, are essential for pollinating flowering plants. This process is vital for the reproduction of many crops and wild plants, supporting agriculture and natural ecosystems.
Soil Fertility and Agriculture : Some animals, such as earthworms and certain insects, enhance soil fertility through their activities, improving soil structure and nutrient availability. This contributes to healthier agricultural systems and sustainable farming practices.
Genetic Diversity : The vast diversity within Animalia contributes to the genetic resources available for breeding and conservation efforts. This diversity is essential for adapting to changing environmental conditions and ensuring the survival of various species.
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