Overview
This lecture covers the major basis of animal classification, details characteristics of different animal phyla, and distinguishes between chordates and non-chordates, including vertebrate classes.
Basis of Classification
- Animals are classified based on cell organization, body symmetry, coelom, segmentation, digestive, circulatory, and reproductive systems.
- Levels of organization: cellular (sponges), tissue (coelenterates), organ (platyhelminthes), and organ-system (annelids, arthropods, etc.).
- Symmetry may be asymmetrical, radial (coelenterates, ctenophores), or bilateral (annelids, arthropods).
- Germ layers: diploblastic (two layers, coelenterates) or triploblastic (three layers, platyhelminthes onwards).
- Coelom types: acoelomate (no cavity, platyhelminthes), pseudocoelomate (cavity not fully lined, aschelminthes), coelomate (true coelom, annelids onward).
- Segmentation (metamerism) is first seen in annelids.
- Notochord, a dorsal rod, characterizes chordates.
Classification of Animals: Key Phyla
- Porifera: Aquatic, asymmetrical, cellular-level, water canal system, internal fertilization, asexual and sexual reproduction.
- Coelenterata (Cnidaria): Aquatic, radial symmetry, tissue-level, cnidoblasts, gastrovascular cavity, polyp & medusa forms.
- Ctenophora: Marine, diploblastic, eight comb plates for locomotion, bioluminescence, only sexual reproduction.
- Platyhelminthes: Flatworms, acoelomate, organ-level, parasitic, hooks, flame cells, high regeneration.
- Aschelminthes: Roundworms, pseudocoelomate, organ-system, complete digestive tract, separate sexes, internal fertilization.
- Annelida: Segmented, coelomate, organ-system, closed circulation, nephridia for excretion, aquatic/terrestrial.
- Arthropoda: Largest phylum, jointed appendages, chitin exoskeleton, open circulation, diverse respiration, malpighian tubules.
- Mollusca: Shell, unsegmented, foot and visceral hump, mantle cavity, radula for feeding, mostly dioecious.
- Echinodermata: Marine, spiny skin, water vascular system, radial symmetry (adults), bilateral larvae, no excretory system.
- Hemichordata: Worm-like, marine, stomochord, organ-system, coelomate, open circulation, gills, proboscis gland.
Phylum Chordata and Its Subphyla
- Chordates: Notochord, dorsal hollow nerve cord, pharyngeal gill slits, post-anal tail, closed circulation, coelomate.
- Urochordata and Cephalochordata: Protochordates, marine, notochord in larval or whole life.
- Vertebrata: Notochord replaced by vertebral column, ventral heart, kidneys, paired appendages.
Vertebrate Classes
- Cyclostomata: Jawless, parasitic, cartilaginous skeleton, no scales/fins, marine-freshwater migration.
- Chondrichthyes: Cartilaginous fishes, ventral mouth, placoid scales, no air bladder, predatory, 2-chambered heart.
- Osteichthyes: Bony fishes, operculum, swim bladder, cycloid/ctenoid scales, mostly oviparous.
- Amphibia: Dual habitat, moist skin, 3-chambered heart, external fertilization, cloaca, oviparous.
- Reptilia: Dry skin, scales/scutes, mostly terrestrial, 3-chambered heart (4 in crocodiles), oviparous, internal fertilization.
- Aves: Feathers, wings, beak, pneumatic bones, 4-chambered heart, warm-blooded, oviparous, air sacs.
- Mammalia: Hair, mammary glands, external ears, differentiated teeth, 4-chambered heart, warm-blooded, primarily viviparous.
Key Terms & Definitions
- Coelom — Body cavity lined by mesoderm.
- Diploblastic — Two germ layers (ectoderm, endoderm).
- Triploblastic — Three germ layers (ectoderm, mesoderm, endoderm).
- Metamerism — Segmentation phenomenon.
- Notochord — Dorsal supporting rod present in chordates.
- Hermaphrodite — Both sexes in one individual.
- Oviparous — Egg-laying organisms.
- Viviparous — Give birth to live young.
- Poikilothermous — Cold-blooded, variable body temperature.
- Homoiothermous — Warm-blooded, constant body temperature.
Action Items / Next Steps
- Complete exercises at the end of the chapter for review.
- Learn distinguishing features and examples of each animal phylum.
- Prepare a list of parasitic animals found in humans as per exercise 15.