Overview
This lecture explains the fundamental basis of animal classification and surveys the key features of major animal phyla and classes, highlighting their structural organization and distinctive traits.
Basis of Classification
- Animals are classified by cellular organization, body symmetry, coelom, segmentation, and notochord presence.
- Levels of organization: cellular (sponges), tissue (cnidarians), organ (platyhelminthes), organ-system (annelids and above).
- Symmetry types: asymmetrical (sponges), radial (cnidarians, ctenophores), bilateral (most others).
- Coelom types: acoelomate (no cavity), pseudocoelomate (false cavity), coelomate (true cavity).
- Germ layers: diploblastic (two layers), triploblastic (three layers).
- Segmentation (metamerism) is first seen in annelids.
- Notochord presence divides animals into chordates and non-chordates.
Animal Phyla Overview
- Porifera: Marine sponges, cellular level, asymmetric, water canal system, intracellular digestion, hermaphrodite.
- Cnidaria: Aquatic, tissue level, radial symmetry, cnidoblasts for stinging, polyp/medusa forms, alternation of generations.
- Ctenophora: Marine, diploblastic, comb plates for locomotion, bioluminescent, sexual reproduction.
- Platyhelminthes: Flatworms, organ level, bilateral, acoelomate, parasitic, flame cells for excretion.
- Aschelminthes: Roundworms, pseudocoelomate, organ-system level, complete digestive tract, sexes separate.
- Annelida: Segmented worms, true coelom, closed circulation, nephridia for excretion, both aquatic and terrestrial.
- Arthropoda: Largest phylum, jointed appendages, exoskeleton, segmented, open circulation, diverse respiratory/excretory organs.
- Mollusca: Soft-bodied, calcareous shell, unsegmented, mantle cavity with gills, radula for feeding.
- Echinodermata: Marine, spiny skin, radial adult symmetry, water vascular system, no excretory organs.
- Hemichordata: Worm-like, three-part body, open circulation, external fertilization, marine.
- Chordata: Notochord, dorsal nerve cord, pharyngeal gill slits, post-anal tail, closed circulation.
Vertebrate Classes
- Cyclostomata: Jawless fish, ectoparasites, cartilaginous skeleton, no paired fins.
- Chondrichthyes: Cartilaginous fishes, ventral mouth, placoid scales, no air bladder, internal fertilization.
- Osteichthyes: Bony fishes, terminal mouth, operculum, air bladder, external fertilization.
- Amphibia: Dual life (water/land), moist skin, three-chambered heart, external fertilization.
- Reptilia: Dry scaly skin, mostly terrestrial, three-chambered (except crocodile), internal fertilization.
- Aves: Feathers, beak, wings, pneumatic bones, four-chambered heart, warm-blooded.
- Mammalia: Hair, mammary glands, external ears, differentiated teeth, four-chambered heart, mostly viviparous.
Key Terms & Definitions
- Coelom — Body cavity lined by mesoderm.
- Diploblastic — Animals with two germ layers (ectoderm, endoderm).
- Triploblastic — Animals with three germ layers (ectoderm, mesoderm, endoderm).
- Notochord — Rod-like supportive structure in chordate embryos.
- Metamerism — Body segmentation with repeating organs.
- Hermaphrodite — Individual producing both eggs and sperm.
- Viviparous/Oviparous — Giving birth to live young / laying eggs.
Action Items / Next Steps
- Review Table 4.2 for summarized features of each animal phylum.
- Complete exercises at the end of the chapter for self-assessment.
- Prepare a list of human parasites as per exercise 15.