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Overview of Animal Anatomy and Classification

Jun 2, 2025

Anatomical Terminology & General Stuff

Symmetry in Animals

  • Spherical symmetry: Bisection through any plane passing through center (e.g., Volvox).
  • Radial symmetry: Bisection into equal halves via central line (e.g., anemones, jellyfish).
  • Bilateral symmetry: Bisection by one plane into relatively equal halves (e.g., planarians, vertebrates).

Circulatory Systems

  • Closed circulatory system: Blood contained within vessels.
  • Open circulatory system: Blood pools within the body.

Kingdom Animalia

  • Multicellular eukaryotic heterotrophs.
  • Excludes prokaryotes, protists, fungi, or plants.
  • Main groups: Invertebrates (no backbone) & Vertebrates (backbone).

Essential Life Functions

  • Feeding: Gathering food.
  • Respiration: Obtaining oxygen.
  • Internal transport: Moving nutrients.
  • Excretion: Removing nitrogenous waste.
  • Sensitivity: Sensing environment.
  • Reproduction: Generating offspring.
  • Movement: Self-explanatory.

Coelom

  • Acoelomates: No coelom (e.g., flatworms).
  • Pseudocoelomates: "False" coelom (e.g., roundworms).
  • Coelomates: True coelom (e.g., annelids, vertebrates).

Phylum Porifera

  • Sponges: Invertebrates, often radially symmetrical.
  • Habitat: Aquatic, mostly marine.
  • Feeding: Filter feeders.
  • Anatomy: Central cavity, osculum, porocytes, spicules, amebocytes, choanocytes.
  • Reproduction: Sexual (hermaphroditic) & asexual (budding).

Phylum Cnidaria

  • Examples: Jellyfish, hydra, anemones, coral.
  • Symmetry: Radial symmetry.
  • Body shapes: Polyp (sessile), Medusa (mobile).
  • Anatomy: Tentacles, gastrovascular cavity, nematocysts.
  • Reproduction: Sexual & asexual (budding).

Phylum Platyhelminthes

  • Flatworms: Tapeworms, planaria.
  • Symmetry: Bilateral.
  • Complexity: Simplest organisms with cephalization.
  • Reproduction: Sexual (hermaphroditic) & asexual (fission).

Phylum Annelida

  • Segmented worms: Earthworms, leeches.
  • System: Closed circulatory system.
  • Reproduction: Hermaphroditic, not self-fertilizing.

Phylum Nematoda

  • Roundworms: Ascaris, hookworms.
  • Symmetry: Bilateral, pseudocoelomates.
  • Reproduction: Sexual, distinct sexes.

Phylum Echinodermata

  • Examples: Sea stars, sea urchins.
  • Symmetry: Pentaradial symmetry.
  • System: Water vascular system.
  • Reproduction: Sexual & asexual (fission).

Phylum Mollusca

  • Examples: Snails, clams, octopus.
  • System: Open (gastropods/bivalves) & closed (cephalopods) circulatory systems.
  • Classes: Gastropoda, Bivalvia, Cephalopoda.

Phylum Arthropoda

  • Examples: Insects, spiders, crabs.
  • System: Open circulatory system.
  • Reproduction: Complete/incomplete metamorphosis.
  • Classes: Insecta, Arachnida, Crustacea.

Phylum Chordata

  • Characteristics: Dorsal nerve cord, notochord, gill slits, post-anal tail.
  • Subphyla: Urochordata, Cephalochordata, Vertebrata.
  • Vertebrates: Fish, birds, reptiles, mammals.

Classifications & Key Features

  • Fish: Agnatha, Chondrichthyes, Osteichthyes.
  • Birds (Aves): Endothermic, feathered.
  • Reptiles: Ectothermic, keratin scales.
  • Mammals: Endothermic, fur/hair, live birth (except Monotremes).