🦁 Zoology &amp; Animal Diversity

Animal Kingdom

Multicellular heterotrophic eukaryotes without cell walls that typically move and ingest food.

Vertebrates and Invertebrates

Vertebrates have a backbone; invertebrates, which are over 95 percent of animals, do not.

Sponges

Simple aquatic animals lacking true tissues that filter feed through pores.

Cnidarians

Radially symmetric animals with stinging cells, including jellyfish, corals and sea anemones.

Flatworms

Soft-bodied, bilaterally symmetric worms with no body cavity, including tapeworms and flukes.

Roundworms

Unsegmented worms with a complete digestive tract, including parasitic hookworms.

Annelids

Segmented worms like earthworms and leeches with a closed circulatory system.

Molluscs

Soft-bodied animals, often with a shell, such as snails, clams and octopuses.

Arthropods

Animals with jointed legs, exoskeleton and segmented bodies, the largest animal phylum.

Insects

Six-legged arthropods with three body parts, often with wings, the most diverse animal group.

Echinoderms

Marine animals with radial symmetry as adults and a water vascular system, like starfish.

Fish

Aquatic, gill-breathing vertebrates, including jawless, cartilaginous and bony fishes.

Amphibians

Vertebrates such as frogs that typically begin life in water and live on land as adults.

Reptiles

Scaly, ectothermic vertebrates that lay shelled eggs on land, including snakes, lizards and turtles.

Birds

Feathered, warm-blooded vertebrates with wings and lightweight bones, most of which fly.

Mammals

Warm-blooded vertebrates with hair that nourish their young with milk.

Intermediate topics (18)

Animal Symmetry

Animals show radial, bilateral or no symmetry, which relates to their lifestyle and movement.

Germ Layers

Ectoderm, mesoderm and endoderm give rise to all animal tissues; simple animals have only two.

Body Cavities

Acoelomate, pseudocoelomate and coelomate animals differ in how the fluid-filled cavity around organs is formed.

Protostomes and Deuterostomes

Two animal lineages differing in embryonic development; deuterostomes include echinoderms and chordates.

Chordate Characteristics

Notochord, dorsal hollow nerve cord, pharyngeal slits and post-anal tail at some stage of life.

Metamorphosis

Dramatic transformation during development, complete in butterflies and gradual in grasshoppers.

Exoskeleton and Moulting

Arthropods shed their rigid chitin covering to grow in a process called ecdysis.

Animal Locomotion

Swimming, walking, flying and burrowing involve specialised skeletons and muscles.

Animal Skeletons

Hydrostatic skeletons, exoskeletons and endoskeletons give support and enable movement.

Digestive Strategies

Herbivores, carnivores and omnivores have teeth and guts adapted to their diet.

Ruminants

Mammals like cows with multi-chambered stomachs that ferment cellulose with microbes.

Marsupials and Monotremes

Marsupials carry young in a pouch; monotremes like the platypus lay eggs.

Thermoregulation in Animals

Endotherms generate heat internally while ectotherms rely on external heat sources.

Hibernation and Torpor

Reduced metabolism and body temperature allow animals to survive scarce winter food.

Animal Migration

Seasonal long-distance movement guided by magnetic, celestial and olfactory cues.

Animal Respiration

Gills, tracheae, book lungs and lungs exchange gases in aquatic and terrestrial animals.

Animal Excretion

Ammonia, urea and uric acid are the nitrogenous wastes of aquatic animals, mammals and birds respectively.

Parasitism in Animals

Parasites such as ticks and tapeworms live on or in hosts, harming them.

Advanced topics (19)

Eusociality

Social organisation with reproductive division of labour, overlapping generations and cooperative care, as in ants and bees.

Insect Haplodiploidy

Males are haploid and females diploid in Hymenoptera, shaping relatedness and sociality.

Bird Flight Adaptations

Hollow bones, keel, air sacs and feathers combine to deliver lift and efficient respiration.

Echolocation

Bats and dolphins emit sounds and interpret echoes to navigate and hunt.

Venom Evolution

Toxins evolved repeatedly from ordinary proteins in snakes, spiders, cone snails and others.

Cephalopod Intelligence

Octopuses and squid have large, complex nervous systems and show learning and problem solving.

Bioluminescence

Light produced by luciferin and luciferase reactions in deep-sea fish, fireflies and jellyfish.

Animal Camouflage and Mimicry

Colour and form evolve to hide or imitate other species, as in Batesian and Mullerian mimicry.

Regeneration

Planarians, starfish and salamanders regrow lost parts using stem cells or dedifferentiation.

Life History Strategies

Trade-offs between growth, reproduction and survival shape clutch size and lifespan.

Animal Phylogenomics

Genome-scale data resolve deep animal relationships, such as ctenophores versus sponges as sister group.

Sexual Dimorphism

Consistent differences in size or appearance between the sexes, shaped by sexual selection.

Parental Care Evolution

Care by one or both parents evolves when benefits to offspring outweigh costs to parents.

Metabolic Scaling

Metabolic rate scales with body mass to the three-quarter power, described by Kleiber's law.

Island Gigantism and Dwarfism

Isolated animals tend to evolve larger or smaller sizes depending on resources and predators.

Animal Cognition

Studies tool use, memory and problem solving in species like crows, primates and cetaceans.

Biomechanics of Locomotion

Applies physics to explain gait, muscle efficiency and fluid dynamics of swimming and flying.

Endangered Animal Biology

Small populations suffer inbreeding depression and demographic risks that conservation breeding tries to reduce.

Domestication Genetics

Selection for tameness changed many traits together, as shown in the Russian fox experiment.