animals

Overview of Animals

  • Animals: Multicellular, heterotrophic (eat other organisms), usually motile (can move).

  • Symmetry:

    • Asymmetrical: No symmetry (e.g., sponges).

    • Radial Symmetry: Multiple mirror-image planes around a central axis (e.g., cnidarians).

    • Bilateral Symmetry: One plane divides the body into left and right halves (e.g., flatworms, humans).

Summary: Animals are classified by symmetry and tissue layers. Sponges are asymmetrical, cnidarians are radially symmetrical, and most others are bilaterally symmetrical.

Germ Layers in Animal Embryos

  • Monoblastic: 1 germ layer (sponges).

  • Diploblastic: 2 layers (ectoderm and endoderm, e.g., cnidarians).

  • Triploblastic: 3 layers (ectoderm, mesoderm, endoderm, e.g., flatworms, earthworms, mollusks).

Sponges (Phylum Porifera)

  • Body: Sessile, porous bodies with an opening (osculum).

  • Water Flow: Water enters through small pores (ostia), into a central cavity (spongocoel), and exits through osculum.

  • Feeding: Choanocytes (collar cells) trap food particles.

  • Support: Silica or calcium-based spicules or collagen fibers.

  • Germ Layer: Monoblastic.

Summary: Sponges are simple animals that filter-feed through a water canal system driven by flagellated cells.

Cnidarians (e.g., Jellyfish, Hydra, Sea Anemones)

  • Symmetry: Radial.

  • Body Forms:

    • Polyp: Vase-shaped, attached.

    • Medusa: Umbrella-shaped, free-swimming.

  • Reproduction:

    • Polyp: Asexual (budding).

    • Medusa: Sexual (egg + sperm → zygote → planula larva → polyp).

  • Structure:

    • 2 germ layers: Ectoderm (epidermis), Endoderm (gastrodermis).

    • Mesoglea: Gel layer in between.

  • Special Cells: Cnidocytes contain nematocysts to sting and paralyze prey.

  • Digestive System: Gastrovascular cavity (one opening = mouth/anus).

Summary: Cnidarians have radial symmetry, two germ layers, and a simple nerve net and stinging cells.

Flatworms (Planaria, Tapeworms)

  • Body: Bilateral symmetry, triploblastic, acoelomate (no body cavity).

  • Digestive System: Mouth, pharynx, branched gut, no anus.

  • Nervous System: Brain-like region, ventral nerve cords, eyespots, auricles.

  • Reproduction: Hermaphroditic, both sexual and asexual.

  • Parasitic Types: Tapeworms and flukes have reduced systems, rely on diffusion for gas/nutrient exchange.

Summary: Flatworms are triploblastic and simple with no coelom. Planaria are free-living, while tapeworms are parasitic.

Roundworms (Ascaris)

  • Symmetry: Bilateral.

  • Body Cavity: Pseudocoelom (not fully lined with mesoderm).

  • Parasitic: Lives in intestines, causes ascariasis.

Summary: Roundworms are pseudocoelomates with a complete digestive tract and a protective outer cuticle.

Segmented Worms (Earthworms)

  • Symmetry: Bilateral, triploblastic, coelomate.

  • Digestive System: Complete (mouth → pharynx → crop → gizzard → intestine → anus).

  • Circulatory System: Closed, with blood vessels and aortic arches (hearts).

  • Nervous System: Brain + ventral nerve cord.

  • Reproduction: Hermaphroditic, clitellum helps form cocoons for fertilized eggs.

  • Movement: Hydrostatic skeleton and bristles (setae) aid in burrowing.

Summary: Earthworms are coelomates with full organ systems and segmented bodies for movement and burrowing.

Mollusks (Clams, Snails, Squids)

  • Body Parts:

    • Foot: Movement.

    • Mantle: Secretes shell.

    • Visceral Mass: Contains organs.

  • Groups:

    • Chitons: 8-plated shells.

    • Bivalves: 2-part shell, filter feeders.

    • Gastropods: Snails and slugs.

    • Cephalopods: Squid, octopus. Intelligent, with arms/tentacles and jet propulsion.

Summary: Mollusks are diverse soft-bodied animals with specialized body parts and coeloms.

Arthropods (Insects, Crustaceans, Spiders, Centipedes)

  • Traits: Segmented bodies, jointed legs, exoskeleton.

  • Groups:

    • Crustaceans: Shrimp, crabs (gills, swimmerets).

    • Hexapods (Insects): Head, thorax, abdomen. Spiracles for breathing.

    • Chelicerates: Spiders (cephalothorax and abdomen).

    • Myriapods: Centipedes, millipedes (many legs).

Summary: Arthropods are extremely diverse, with exoskeletons, jointed limbs, and segmented bodies.

Deuterostomes

  • Blastopore becomes anus (vs. mouth in protostomes).

  • Includes: Echinoderms and Chordates.

Echinoderms (Sea Stars, Urchins)

  • Symmetry: Bilateral larvae, radial adults.

  • Movement: Water vascular system (tube feet, madreporite).

  • Digestive System: Mouth (oral side) → stomach → anus (aboral side).

  • Nervous System: Nerve ring, simple.

Chordates (Humans, Fish, Amphibians, Birds, Mammals)

  • 4 Features: Dorsal nerve cord, notochord, pharyngeal slits, post-anal tail.

  • Subgroups:

    • Lancelets: All 4 traits entire life.

    • Tunicates: Traits in larval stage.

    • Vertebrates: Have a backbone, brain, and spinal cord.

Vertebrates

  • Jawless Fish: Lampreys (suckers, no jaws).

  • Cartilaginous Fish: Sharks (jaws, cartilage skeleton).

  • Bony Fish: Swim bladder, gills, operculum.

  • Amphibians: Water-dependent eggs, metamorphosis.

  • Reptiles: Scales, internal fertilization, amniotic egg.

  • Birds: Feathers, beaks, flight adaptations.

  • Mammals: Hair, mammary glands, endothermic.

Homologous vs. Analogous Structures

  • Homologous: Same origin, different function (e.g., human arm vs. bird wing).

  • Analogous: Same function, different origin (e.g., bird wing vs. insect wing).

Human vs. Chimp Skulls

  • Differences:

    • Humans: Smaller teeth, larger brain, flat face, foramen magnum centered (upright posture).

    • Chimps: Larger teeth, protruding face, foramen magnum at the back (quadrupedal posture).