Chapter 4 Animal Kingdom

Animal Kingdom

  • Observation shows various animals with distinct structures and forms; over a million species classified.

  • Classification aids the systematic positioning of newly described species.

Basis of Classification

In spite of structural differences, fundamental features common to various individuals include:

  • Arrangement of Cells

  • Body Symmetry

  • Nature of Coelom

  • Patterns of Digestive, Circulatory, and Reproductive Systems

4.1.1 Levels of Organisation

  • All members of Animalia are multicellular but exhibit different cell organisation.

    • Cellular Level: e.g., sponges - loose cell aggregates.

    • Tissue Level: e.g., coelenterates - cells are arranged into tissues.

    • Organ Level: e.g., Platyhelminthes - tissues grouped into organs.

    • Organ System Level: e.g., Annelids, Arthropods, Molluscs - organs form systems for specific physiological functions.

4.1.2 Symmetry

  • Asymmetrical: e.g., Sponges - lack symmetry.

  • Radial Symmetry: Coelenterates, Ctenophores, Echinoderms - can be divided into two identical halves along any plane.

  • Bilateral Symmetry: Annelids, Arthropods - can be divided into two identical halves along one plane only.

4.1.3 Diploblastic and Triploblastic Organisation

  • Diploblastic Animals: e.g., Coelenterates - have two embryonic layers (ectoderm and endoderm) with mesoglea in between.

  • Triploblastic Animals: e.g., Platyhelminthes to Chordates - have an additional mesoderm layer.

4.1.4 Coelom

  • Coelomates: Animals with a coelom lined by mesoderm (e.g., Annelids, Molluscs).

  • Pseudocoelomates: Animals with a body cavity not entirely lined by mesoderm (e.g., Aschelminthes).

  • Acoelomates: Animals without a body cavity (e.g., Platyhelminthes).

4.1.5 Segmentation

  • Metameric Segmentation: e.g., Earthworm - body divided into segments with repetition of organs.

4.1.6 Notochord

  • The notochord is a rod-like structure in some animals during embryonic development.

    • Animals with notochord are called Chordates; those without are Non-Chordates.

Classification of Animals

Broad classifications based on fundamental features are as follows:

4.2.1 Phylum – Porifera

  • Common Name: Sponges

  • Characteristics: Mostly asymmetrical, marine, cellular level of organisation.

  • Water Transport System: Water enters through pores (ostia), into spongocoel, exits through osculum.

    • Digestive Process: Intracellular digestion.

  • Reproduction: Hermaphroditic (both sexes in one individual), asexual via fragmentation and sexual via gamete formation.

4.2.2 Phylum – Coelenterata (Cnidaria)

  • Characteristics: Aquatic, mostly marine, radially symmetrical.

  • Digestion: Extracellular and intracellular within a central gastro-vascular cavity; two forms - polyp (sessile) and medusa (free-swimming).

  • Reproduction: Alternation of generation (Metagenesis).

  • Examples: Physalia, Adamsia, Pennatula.

4.2.3 Phylum – Ctenophora

  • Common Name: Sea walnuts or comb jellies

  • Features: Marine, radially symmetrical, diploblastic with eight ciliated comb plates for locomotion. Bioluminescent properties; reproduction is only sexual.

4.2.4 Phylum – Platyhelminthes

  • Common Name: Flatworms

  • Features: Dorso-ventrally flattened, mostly endoparasites, bilateral, triploblastic, acoelomate.

4.2.5 Phylum – Aschelminthes

  • Common Name: Roundworms

  • Characteristics: Circular cross-section, may be free-living or parasitic, organ system level of organisation, bilaterally symmetrical, pseudocoelomate.

4.2.6 Phylum – Annelida

  • Characteristics: Segmented body (metamerically), coelomate animals, organ-system organisation.

4.2.7 Phylum – Arthropoda

  • Largest Phylum: Includes insects, diverse forms, jointed appendages, segmented bodies.

4.2.8 Phylum – Mollusca

  • Characteristics: Terrestrial or aquatic, coelomate, unsegmented body covered by shell.

4.2.9 Phylum – Echinodermata

  • Features: Marine animals with radial symmetry, unique water vascular system, endoskeleton.

4.2.10 Phylum – Hemichordata

  • Characteristics: Worm-like marine animals, possess a stomochord.

4.2.11 Phylum – Chordata

  • Fundamental Characteristics: Presence of notochord, dorsal hollow nerve cord, pharyngeal gill slits.

    • Subphyla: Urochordata, Cephalochordata, Vertebrata.

Classifications under Chordata

  1. Cyclostomata: Jawless fish, ectoparasites.

  2. Chondrichthyes: Cartilaginous fish, powerful jaws, cold-blooded.

  3. Osteichthyes: Bony fish, air bladder for buoyancy.

  4. Amphibia: Dual life in water and land.

  5. Reptilia: Terrestrial with dry skin and internal fertilisation.

  6. Aves: Birds, warm-blooded.

  7. Mammalia: Diverse habitats, mammary glands for nourishment.

Summary of Animal Kingdom Classification

  • Classification based on fundamental characteristics like level of organisation, symmetry, cell organisation, type of coelom, and more ultimately helps in categorizing the Animal Kingdom, understanding evolutionary relationships and biological diversity.

Exercises

  1. Discuss classification difficulties without considering fundamental features.

  2. Outline the steps for classifying a given specimen.

  3. Evaluate the importance of body cavity and coelom in animal classification.

Animal Kingdom

Observation shows various animals with distinct structures and forms, with over a million species classified within the Animalia kingdom. This classification aids in the systematic positioning of newly described species, allowing for better understanding of evolutionary relationships and biological diversity.

Basis of Classification

In spite of structural differences, fundamental features common to various individuals include:

  • Arrangement of Cells: Reflects the organization level among different animal groups.

  • Body Symmetry: Provides insights into the evolutionary and functional aspects of animals.

  • Nature of Coelom: The presence or absence of body cavities informs classification.

  • Patterns of Digestive, Circulatory, and Reproductive Systems: Variations in these systems illustrate the adaptability and evolutionary changes in different environments.

4.1.1 Levels of Organisation

All members of Animalia are multicellular but exhibit different levels of cell organization:

  • Cellular Level: e.g., sponges, which display a loose aggregation of cells instead of true tissue.

  • Tissue Level: e.g., coelenterates like jellyfish, where cells are organized into true tissues performing specific functions.

  • Organ Level: e.g., Platyhelminthes (flatworms), featuring tissues grouped into organs for more complex interactions.

  • Organ System Level: e.g., Annelids, Arthropods, and Molluscs, where organs collaborate to form systems that support physiological functions like digestion, circulation, and reproduction.

4.1.2 Symmetry

  • Asymmetrical: e.g., Sponges - lack any symmetrical form.

  • Radial Symmetry: Found in Cnidarians (like jellyfish) and Echinoderms (like starfish), they can be divided into two identical halves along multiple planes.

  • Bilateral Symmetry: Present in Annelids, Arthropods, and most higher animals, allowing division into two identical halves along a single plane, facilitating more complex movement and processing of sensory information.

4.1.3 Diploblastic and Triploblastic Organisation

  • Diploblastic Animals: e.g., Coelenterates which have two embryonic layers (ectoderm and endoderm) and a non-cellular jelly-like mesoglea in between, representing a simpler structure.

  • Triploblastic Animals: e.g., from Platyhelminthes to Chordates, characterized by an additional third layer of cells (mesoderm), contributing to more complex body plans and systems.

4.1.4 Coelom

  • Coelomates: Animals with a true coelom (body cavity) lined by mesoderm, crucial for supporting internal organs (e.g., Annelids and Molluscs).

  • Pseudocoelomates: Animals like Aschelminthes that have a body cavity not completely lined by mesoderm, resulting in less complex organ systems.

  • Acoelomates: Such as Platyhelminthes, that lack a body cavity altogether, leading to simpler internal structures.

4.1.5 Segmentation

  • Metameric Segmentation: e.g., Earthworm - the body is divided into segments, allowing for redundant organ systems and more efficient movement.

4.1.6 Notochord

The notochord is a rod-like structure present during embryonic development in some animals. Animals possessing a notochord are classified as Chordates, whereas those lacking it are referred to as Non-Chordates.

Classification of Animals

Broad classifications based on fundamental features include:

4.2.1 Phylum – Porifera

  • Common Name: Sponges

  • Characteristics: Mostly asymmetrical, primarily marine; classified at the cellular level.

  • Water Transport System: Water enters through numerous tiny pores (ostia), moves into a central cavity (spongocoel), then exits through a larger opening (osculum).

  • Digestive Process: Characterized by intracellular digestion, where food is processed within cells rather than being broken down in a body cavity.

  • Reproduction: Typically hermaphroditic (containing both male and female reproductive organs), capable of both asexual reproduction through fragmentation and sexual reproduction via gamete formation.

4.2.2 Phylum – Coelenterata (Cnidaria)

  • Characteristics: Aquatic, predominantly marine, exhibit radial symmetry.

  • Digestion: Employ extracellular digestion occurring within a central gastro-vascular cavity, having two distinct forms: polyp (sessile) for a stationary lifestyle, and medusa (free-swimming) for locomotion.

  • Reproduction: Follows a pattern of alternation of generations (Metagenesis).

  • Examples: Includes organisms such as Physalia (Portuguese Man o' war), Adamsia (sea anemones), and Pennatula (sea pens).

4.2.3 Phylum – Ctenophora

  • Common Name: Sea walnuts or comb jellies

  • Features: Reside in marine environments, display radial symmetry with a diploblastic structure. Notable for eight ciliated comb plates aiding in locomotion, and are known for their bioluminescent properties. Reproduction occurs solely through sexual means.

4.2.4 Phylum – Platyhelminthes

  • Common Name: Flatworms

  • Features: Exhibit dorso-ventrally flattened bodies, predominantly endoparasitic, bilaterally symmetrical, triploblastic, and classified as acoelomates.

4.2.5 Phylum – Aschelminthes

  • Common Name: Roundworms

  • Characteristics: Characterized by a circular cross-section, these organisms may be either free-living or parasitic, possessing an organ system level of organization, displaying bilateral symmetry, and classified as pseudocoelomates.

4.2.6 Phylum – Annelida

  • Characteristics: Feature a segmented body plan (metamerically structured) and are classified as coelomate animals with organ-system level organization, contributing to a greater complexity of physiology and movement.

4.2.7 Phylum – Arthropoda

  • Largest Phylum: Includes insects and other arthropods, characterized by diverse forms, jointed appendages, sophisticated nervous systems, and segmented bodies.

4.2.8 Phylum – Mollusca

  • Characteristics: Exhibits diversity in habitat (terrestrial or aquatic), coelomate structure, typically an unsegmented body covered by a hard shell, which can serve as protection, buoyancy, or growth.

4.2.9 Phylum – Echinodermata

  • Features: Comprised of marine animals showing radial symmetry and a unique water vascular system facilitating movement and feeding, alongside an internal skeleton (endoskeleton).

4.2.10 Phylum – Hemichordata

  • Characteristics: Comprise worm-like marine animals, featuring a structure known as stomochord, which contributes to their classification but not a true notochord as in Chordates.

4.2.11 Phylum – Chordata

  • Fundamental Characteristics: Defined by the presence of a notochord, dorsal hollow nerve cord, and pharyngeal gill slits during some stage of development.

  • Subphyla: Includes Urochordata (tunicates), Cephalochordata (lancelets), and Vertebrata (vertebrates).

Classifications under Chordata

  • Cyclostomata: Jawless fish such as lampreys and hagfish, known for being ectoparasites.

  • Chondrichthyes: Cartilaginous fish including sharks and rays, recognized for having powerful jaws and being cold-blooded.

  • Osteichthyes: Bony fish characterized by an air bladder for buoyancy and complex structures.

  • Amphibia: Exhibit dual life cycles, inhabiting both aquatic and terrestrial environments, displaying an affinity for moist habitats.

  • Reptilia: Terrestrial animals equipped with dry skin and internal fertilization, adapting to life on land.

  • Aves: Birds characterized by feathers, warm-blooded physiology, and specialized adaptations for flight.

  • Mammalia: Demonstrates a wide range of habitats, distinguished by mammary glands for nourishing offspring with milk.

Summary of Animal Kingdom Classification

The classification based on fundamental characteristics such as levels of organisation, symmetry, cell organization, type of coelom, and body structure proves essential in categorizing the Animal Kingdom, highlighting the evolutionary relationships and biological diversity that have arisen throughout the history of life on Earth.