Animal Kingdom

Key Concepts

Basis of Classification

Animals are classified based on fundamental features:

Levels of Organization:
- Cellular level: Cells are loose aggregates (e.g., Sponges).
- Tissue level: Cells perform the same function in tissues (e.g., Coelenterates).
- Organ level: Tissues grouped into organs (e.g., Platyhelminthes).
- Organ system level: Organs associate to form functional systems (e.g., Annelids, Arthropods, Chordates).
Circulatory System:
- Open type: Blood is pumped out of the heart; tissues are bathed in it.
- Closed type: Blood circulates through a series of vessels.
Symmetry:
- Asymmetrical: Cannot be divided into equal halves (e.g., most Sponges).
- Radial symmetry: Any plane passing through the central axis divides the body into identical halves (e.g., Coelenterates, Ctenophores, Echinoderms).
- Bilateral symmetry: Body divided into identical left and right halves in only one plane (e.g., Annelids, Arthropods).
Diploblastic and Triploblastic Organization:
- Diploblastic: Cells in two embryonic layers (ectoderm and endoderm) with a middle mesoglea (e.g., Coelenterates).
- Triploblastic: Three germinal layers (ectoderm, mesoderm, endoderm) (e.g., Platyhelminthes to Chordates).
Coelom (Body Cavity):
- Acoelomates: No body cavity (e.g., Platyhelminthes).
- Pseudocoelomates: Cavity not lined by mesoderm (e.g., Aschelminthes).
- Coelomates: Cavity lined by mesoderm (e.g., Annelids to Chordates).
Segmentation: Metameric segmentation (metamerism) is found in animals like earthworms.
Notochord: A mesodermally derived rod-like structure on the dorsal side. Present in Chordates, absent in Non-chordates.

Classification of Animals (Non-Chordates)

Porifera (Sponges): Cellular level, water canal system (ostia, spongocoel, osculum), choanocytes (collar cells), internal fertilization.
Coelenterata (Cnidaria): Tissue level, radial symmetry, cnidoblasts (stinging cells), two body forms: Polyp (sessile) and Medusa (free-swimming). Exhibit metagenesis (e.g., Obelia).
Ctenophora (Sea Walnuts): Exclusively marine, 8 rows of ciliated comb plates, bioluminescence.
Platyhelminthes (Flatworms): Dorso-ventrally flattened, acoelomate, flame cells for excretion, high regeneration capacity (e.g., Planaria).
Aschelminthes (Roundworms): Circular cross-section, pseudocoelomate, separate sexes (dioecious).
Annelida: Metamerically segmented, closed circulatory system, nephridia for excretion, parapodia in aquatic forms (Nereis).
Arthropoda: Largest phylum, chitinous exoskeleton, jointed appendages, malpighian tubules for excretion, open circulatory system.
Mollusca: Second largest phylum, soft body with calcareous shell, muscular foot, visceral hump, radula for feeding.
Echinodermata: Spiny-bodied, spiny skin, water vascular system, adults are radially symmetrical, larvae are bilaterally symmetrical.

Water Vascular System Unique to Echinoderms, this system helps in locomotion, capture and transport of food, and respiration. It is different from the water canal system of sponges.

Hemichordata: Worm-like marine animals, body divided into proboscis, collar, and trunk.

Phylum Chordata

Characterized by a notochord, dorsal hollow nerve cord, and paired pharyngeal gill slits.

Subphyla:
- Urochordata: Notochord in larval tail only.
- Cephalochordata: Notochord from head to tail, persistent.
- Vertebrata: Notochord replaced by vertebral column.
Classes of Vertebrata:
1. Cyclostomata: Jawless, ectoparasites on fishes, circular mouth.
2. Chondrichthyes: Cartilaginous fishes, placoid scales, lack air bladder (e.g., Sharks).
3. Osteichthyes: Bony fishes, operculum over gills, air bladder present.
4. Amphibia: Dual life (land and water), moist skin, three-chambered heart.
5. Reptilia: Creeping/crawling, dry cornified skin, three-chambered heart (four in crocodiles).
6. Aves (Birds): Feathers, pneumatic (hollow) bones, four-chambered heart, warm-blooded.
7. Mammalia: Mammary glands, hair on skin, four-chambered heart, mostly viviparous.

Key Concepts

Animals are classified based on fundamental features:

Levels of Organization:

Cellular level: Cells are loose aggregates (e.g., Sponges).
Tissue level: Cells perform the same function in tissues (e.g., Coelenterates).
Organ level: Tissues grouped into organs (e.g., Platyhelminthes).
Organ system level: Organs associate to form functional systems (e.g., Annelids, Arthropods, Chordates).

Circulatory System:

Open type: Blood is pumped out of the heart; tissues are bathed in it.
Closed type: Blood circulates through a series of vessels.

Symmetry:

Asymmetrical: Cannot be divided into equal halves (e.g., most Sponges).
Radial symmetry: Any plane passing through the central axis divides the body into identical halves (e.g., Coelenterates, Ctenophores, Echinoderms).
Bilateral symmetry: Body divided into identical left and right halves in only one plane (e.g., Annelids, Arthropods).

Diploblastic and Triploblastic Organization:

Diploblastic: Cells in two embryonic layers (ectoderm and endoderm) with a middle mesoglea (e.g., Coelenterates).
Triploblastic: Three germinal layers (ectoderm, mesoderm, endoderm) (e.g., Platyhelminthes to Chordates).

Coelom (Body Cavity):

Acoelomates: No body cavity (e.g., Platyhelminthes).
Pseudocoelomates: Cavity not lined by mesoderm (e.g., Aschelminthes).
Coelomates: Cavity lined by mesoderm (e.g., Annelids to Chordates).

Segmentation: Metameric segmentation (metamerism) is found in animals like earthworms.

Notochord: A mesodermally derived rod-like structure on the dorsal side. Present in Chordates, absent in Non-chordates.

Porifera (Sponges): Cellular level, water canal system (ostia, spongocoel, osculum), choanocytes (collar cells), internal fertilization.

Coelenterata (Cnidaria): Tissue level, radial symmetry, cnidoblasts (stinging cells), two body forms: Polyp (sessile) and Medusa (free-swimming). Exhibit metagenesis (e.g., Obelia).

Ctenophora (Sea Walnuts): Exclusively marine, 8 rows of ciliated comb plates, bioluminescence.

Platyhelminthes (Flatworms): Dorso-ventrally flattened, acoelomate, flame cells for excretion, high regeneration capacity (e.g., Planaria).

Aschelminthes (Roundworms): Circular cross-section, pseudocoelomate, separate sexes (dioecious).

Annelida: Metamerically segmented, closed circulatory system, nephridia for excretion, parapodia in aquatic forms (Nereis).

Arthropoda: Largest phylum, chitinous exoskeleton, jointed appendages, malpighian tubules for excretion, open circulatory system.

Mollusca: Second largest phylum, soft body with calcareous shell, muscular foot, visceral hump, radula for feeding.

Echinodermata: Spiny-bodied, spiny skin, water vascular system, adults are radially symmetrical, larvae are bilaterally symmetrical.

Water Vascular System Unique to Echinoderms, this system helps in locomotion, capture and transport of food, and respiration. It is different from the water canal system of sponges.

Hemichordata: Worm-like marine animals, body divided into proboscis, collar, and trunk.

Characterized by a notochord, dorsal hollow nerve cord, and paired pharyngeal gill slits.

Subphyla:

Urochordata: Notochord in larval tail only.
Cephalochordata: Notochord from head to tail, persistent.
Vertebrata: Notochord replaced by vertebral column.

Classes of Vertebrata:

Cyclostomata: Jawless, ectoparasites on fishes, circular mouth.
Chondrichthyes: Cartilaginous fishes, placoid scales, lack air bladder (e.g., Sharks).
Osteichthyes: Bony fishes, operculum over gills, air bladder present.
Amphibia: Dual life (land and water), moist skin, three-chambered heart.
Reptilia: Creeping/crawling, dry cornified skin, three-chambered heart (four in crocodiles).
Aves (Birds): Feathers, pneumatic (hollow) bones, four-chambered heart, warm-blooded.
Mammalia: Mammary glands, hair on skin, four-chambered heart, mostly viviparous.

Animal Kingdom

Animal Kingdom

Key Concepts

Basis of Classification

Classification of Animals (Non-Chordates)

Phylum Chordata

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Animal Kingdom

Animal Kingdom

Key Concepts

Basis of Classification

Classification of Animals (Non-Chordates)

Phylum Chordata

On this page