Animal Kingdom

Without fundamental features (like symmetry, levels of organisation, or coelom), classification would be chaotic and unscientific. It would be impossible to:

• Study millions of species individually.
• Assign a systematic position to newly described species.
• Understand the evolutionary relationships and complexities between different groups.

The steps to classify a specimen involve observing its:

1. Level of Organisation: Cellular, tissue, organ, or organ system.
2. Symmetry: Asymmetrical, radial, or bilateral.
3. Germ Layers: Diploblastic or Triploblastic.
4. Body Cavity (Coelom): Acoelomate, Pseudocoelomate, or Coelomate.
5. Segmentation: Presence or absence of metamerism.
6. Presence of Notochord: To distinguish between Chordates and Non-chordates.

The coelom is a key diagnostic feature. It helps us understand the complexity of the organism. For example:

• Acoelomates lack a cavity, indicating simpler body plans (e.g., Platyhelminthes).
• Pseudocoelomates show primitive cavities (e.g., Aschelminthes).
• Coelomates have a true cavity lined by mesoderm, allowing for more complex organ development (e.g., Annelida to Chordata).

Intracellular Digestion: Occurs within the cytoplasm of the cell. Common in lower animals like Sponges (Porifera).

Extracellular Digestion: Occurs outside the cells, usually in a specialized cavity or lumen. Seen in Coelenterates and all higher animals.

Direct Development: The young ones resemble the adult in form. There is no larval stage (e.g., Humans).

Indirect Development: The animal passes through a larval stage which is morphologically distinct from the adult (e.g., Frog, Butterfly).

Parasitic flatworms show several adaptations:

• Presence of hooks and suckers for attachment.
• Thick tegument to protect against host digestive juices.
• Absence of a digestive system (nutrients absorbed via body surface).
• High reproductive potential and specialized flame cells.

Arthropods are successful due to:

• Chitinous Exoskeleton: Provides protection and prevents water loss.
• Jointed Appendages: Provide mobility and adaptability.
• Highly developed sensory and respiratory systems.

(c) Echinodermata. (Used for locomotion, capture and transport of food).

In Vertebrata, the embryonic notochord is replaced by a vertebral column in the adult. Protochordates have a notochord but never develop a vertebral column, so they are chordates but not vertebrates.

The air bladder regulates buoyancy, allowing bony fishes to stay at a certain depth without constant swimming to avoid sinking.

• Forelimbs modified into wings and presence of feathers.
• Pneumatic bones (hollow bones) to reduce weight.
• Air sacs connected to lungs for efficient respiration.

Oviparous mothers lay more eggs because eggs outside the body are more vulnerable to predators and environment; high numbers ensure species survival.

(c) Annelida. (Metameric segmentation).

(a) Operculum — Osteichthyes | (b) Parapodia — Annelida | (c) Scales — Reptilia | (d) Comb plates — Ctenophora | (e) Radula — Mollusca | (f) Hairs — Mammalia | (g) Choanocytes — Porifera | (h) Gill slits — Chondrichthyes

1. Tapeworm (Taenia)
2. Roundworm (Ascaris)
3. Filaria worm (Wuchereria)
4. Hookworm (Ancylostoma)