Animal Kingdom

Importance of Classification

• Over a million animal species described.
• Classification aids in systematic positioning of new species.

Basis of Classification

• Common features in cell arrangement, symmetry, coelom, digestive, circulatory, and reproductive systems.

Levels of Organisation

• Cellular Level: Sponges.
• Tissue Level: Coelenterates.
• Organ Level: Platyhelminthes.
• Organ System Level: Annelids, Arthropods, Molluscs, Echinoderms, Chordates.
  • Complexity varies in digestive and circulatory systems.

Symmetry

• Asymmetrical: Sponges.
• Radial Symmetry: Coelenterates, ctenophores, echinoderms.
• Bilateral Symmetry: Annelids, arthropods.

Diploblastic and Triploblastic Organisation

• Diploblastic: Two embryonic layers (ectoderm, endoderm), e.g., coelenterates.
• Triploblastic: Three layers with mesoderm, e.g., platyhelminthes to chordates.

Coelom

• Coelomates: True coelom, e.g., annelids, molluscs.
• Pseudocoelomates: Coelom not fully lined by mesoderm, e.g., aschelminthes.
• Acoelomates: No coelom, e.g., platyhelminthes.

Segmentation

• Serial repetition of body segments, e.g., earthworm (metamerism).

Notochord

• Rod-like structure in chordates during embryonic development.

Classification of Animals

• Phyla classification based on fundamental features.

Phylum Porifera

• Commonly known as sponges.
• Marine, asymmetrical, cellular level of organisation.
• Water transport system for feeding and respiration.

Phylum Coelenterata (Cnidaria)

• Aquatic, radially symmetrical, diploblastic.
• Tissue level organisation, presence of cnidoblasts.
• Alternation of generations in some species.

Phylum Ctenophora

• Marine, radially symmetrical, diploblastic.
• Ciliated comb plates for locomotion.

Phylum Platyhelminthes

• Flatworms, bilateral symmetry, triploblastic, acoelomates.
• Parasitic forms have suckers, high regeneration capacity in some.

Phylum Aschelminthes

• Roundworms, pseudocoelomates, bilateral symmetry.
• Complete alimentary canal, separate sexes.

Phylum Annelida

• Segmented worms, coelomates.
• Exhibit metamerism, closed circulatory system.

Phylum Arthropoda

• Largest phylum, includes insects.
• Jointed appendages, chitinous exoskeleton.

Phylum Mollusca

• Second largest phylum.
• Body covered by calcareous shell, soft body, radula for feeding.

Phylum Echinodermata

• Marine, spiny bodied, radial symmetry.
• Water vascular system for movement and feeding.

Phylum Hemichordata

• Marine, worm-like, rudimentary notochord-like structure.

Phylum Chordata

• Presence of notochord, dorsal nerve cord, gill slits.
• Subdivisions: Urochordata, Cephalochordata, Vertebrata.

Classifications within Vertebrata

• Cyclostomata: Jawless, ectoparasites.
• Chondrichthyes: Cartilaginous fishes.
• Osteichthyes: Bony fishes.
• Amphibia: Dual life, aquatic & terrestrial.
• Reptilia: Terrestrial, scaly skin.
• Aves: Feathers, flight adaptations.
• Mammalia: Mammary glands, hair, viviparous.

Summary

• Fundamental features assist in broad classification.
• Specific features distinguish each phylum/class.

Exercises

• Questions on classification challenges, coelom importance, digestion types, and evolutionary traits among others.