Introduction to Animals Vocabulary

Animals

• Animals range from sponges to humans.
• They play key roles in ecosystems.
• Over 1.4 million species have been described, and many more are yet to be discovered.
• Scientists are in a race to discover and describe more animal species before they become extinct.
• Definition of Animal: A multicellular, eukaryotic, heterotrophic organism that moves at some life stage.
• Biodiversity: The variety of life in the world or in a particular habitat.
• Real-World Example: Coral reefs house thousands of animal species but are threatened by climate change.

Key Animal Features

• Multicellular with no cell walls.
• Heterotrophic (must consume others for food).
• Contain extracellular matrix (ECM) for support.
• Have neurons and muscle cells (except sponges).
• Definition of ECM: A network of proteins like collagen that provides structural support to cells.
• Real-World Connection: Your skin’s elasticity and wound healing come from ECM proteins.

Evolutionary Origins

• Animals are monophyletic, all descended from a common ancestor.
• Closest relatives: Choanoflagellates (single-celled eukaryotes).
• Last common ancestor lived ~900 million years ago.
• Definition of Monophyletic: A group that includes a common ancestor and all its descendants.
• Real-World Example: The feeding cells of sponges resemble choanoflagellates, showing an evolutionary link.

Drivers of Animal Diversification

• High oxygen levels → larger bodies.
• Predation drove evolution of mobility and defense.
• New niches triggered adaptive radiation.
• Real-World Example: The Cambrian Explosion was a rapid diversification of animals, like nature's "startup boom."

Evolutionary Origins (Phyla)

• Around 30–35 recognized phyla.
• Three major groupings:
  • Non-Bilaterians (e.g., sponges).
  • Protostomes (e.g., insects, mollusks).
  • Deuterostomes (e.g., humans, sea stars).

Animal Phyla Overview

• Non-bilaterian Groups:
  • Placozoa: Placozoans, 1 species.
  • Ctenophora: Comb jellies, 190 species.
  • Acoela: Acoelomate worms, 350 species.
  • Porifera: Sponges, 8500 species.
  • Cnidaria: Jellyfish, corals, anemones, hydroids, sea fans, 11,500 species.
• Protostomes:
  • Chaetognatha: Arrow worms, pterobranchs, 120 species.
• Protostomes: Lophotrochozoa:
  • Phoronida: Horseshoe worms, 10 species.
  • Gnathostomulida: Gnathostomulids, 100 species.
  • Entoprocta: Entoprocts, kamptozoans, 170 species.
  • Gastrotricha: Gastrotrichs, 400 species.
  • Brachiopoda: Brachiopods (lamp shells), 550 species.
  • Acanthocephala: Acanthocephalans, 1150 species.
  • Nemertea: Ribbon worms, 1200 species.
  • Rotifera: Rotifers, 2100 species.
  • Bryozoa: Bryozoans, ectoprocts, moss animals, 5700 species.
  • Annelida: Segmented worms, 16,800 species.
  • Platyhelminthes: Flatworms, 20,000 species.
  • Mollusca: Mollusks (clams, snails, octopuses), 85,000 species.
• Protostomes: Ecdysozoa:
  • Priapulida: Priapulids, 16 species.
  • Kinorhyncha: Kinorhynchs, 130 species.
  • Onychophora: Velvet worms, 165 species.
  • Nematomorpha: Hair worms, 330 species.
  • Tardigrada: Water bears, 1045 species.
  • Nematoda: Roundworms, 25,000 species.
  • Arthropoda: Arthropods (spiders, insects, crustaceans), 1,200,000 species.
• Deuterostomes:
  • Hemichordata: Acorn worms, 108 species.
  • Echinodermata: Echinoderms (sea stars, sea urchins, sea cucumbers), 7000 species.
  • Chordata: Chordates: tunicates, lancelets, sharks, bony fishes, amphibians, reptiles (including birds), mammals, 65,000 species.

Tools to Study Animal Evolution

• Fossils: Show morphology, timeline, and location of death but do not represent all animals equally.
• Comparative morphology: Reveals shared traits (body plan).
• Comparative development: Highlights gene expression and morphological changes that result.
• Comparative genomics: Analyzes genetic similarities.
• Real-World Example: Modern DNA testing (used in ancestry kits) uses the same principle as comparative genomics.

Sponges-First Hypothesis

• Sponges appear earliest in the fossil record.
• They have a simple body plan, no nerves or true tissues.
• Sessile: Fixed in one place, immobile.
• Benthic: Live at the bottom of aquatic environments.
• Similar feeding cells to choanoflagellates.
• Real-World Example: Like barnacles on a rock, sponges don't move but filter water for food.

Germ Layers and Tissue Origins

• Diploblasts: 2 tissue layers (ectoderm + endoderm).
• Triploblasts: 3 layers (ectoderm + endoderm + mesoderm).
• Ectoderm (“outside-skin”).
• Endoderm (“inside-skin”).
• Mesoderm forms muscle, organs, bones, etc.

Tissue Origin and Diversification

• Traditionally, two groups of animals are recognized as diploblasts:
  • Ctenophora (comb jellies).
  • Cnidaria (jellyfish, corals, sea pens, hydra, and anemones).

Shared Genetic Roots of Muscle Movement

• All animals share homologous genes for contractile proteins, including actin and myosin.
• In animals like ctenophores (comb jellies) and cnidarians (jellyfish), epitheliomuscular cells perform muscle-like contractions.
• These cells come from outer tissue layers (ectoderm or endoderm) and are not true muscle cells from mesoderm, but they work in similar ways.
• Epitheliomuscular cells: Specialized cells that combine features of epithelial (surface) cells and muscle cells to allow movement, even in animals without mesoderm.

Symmetry Types

• Radial symmetry: Body arranged around a central axis; multiple planes of symmetry.
  • Example: Jellyfish.
• Bilateral symmetry: One plane of symmetry; distinct front/back and left/right.
  • Example: Humans.

Coelom: The Body Cavity

• A coelom is a fluid-filled cavity that allows internal organs to grow, move, and function independently of the outer body wall.
• Types of Coeloms:
  • Coelomate: Cavity fully lined with mesoderm.
    • Example: Earthworm.
    • Your abdominal cavity is a true coelom, giving organs flexibility for digestion and movement.
  • Pseudocoelomate: Cavity partially lined with mesoderm.
    • Example: Roundworm.
  • Acoelomate: No coelom; organs embedded directly in tissue.
    • Example: Flatworm.

Protostomes vs. Deuterostomes

• Protostomes: Mouth forms before anus.
• Deuterostomes: Anus forms before mouth.
• Determined during gastrulation.
• Three embryonic germ layers form during gastrulation.
• In deuterostomes: Blastopore becomes anus and mouth forms later.
• Real-World Connection: You’re a deuterostome!

Nervous System and Cephalization

• Cephalization = evolution of a head with sensory organs.
• The nervous system ranges from nerve nets to centralized brains.
• Nervous System Evolution:
  • Sponges: No nervous system or neurons.
  • Cnidarians and ctenophores:
    • Possess a nerve net a simple, decentralized web of neurons.
    • Can detect and respond to touch, light, and chemicals from all directions.
  • Definition: Ganglia clusters of nerve cells that process information.
  • Bilaterians:
    • Have a more complex central nervous system (CNS).
    • Includes ganglia clusters of nerve cells that process and relay signals.

Segmentation in Animals

• Repeating body segments.
• Seen in annelids (worms), arthropods (insects), vertebrates.
• Allows for specialized functions and complex movement.
• Definition: Segmentation division of the body into repeated parts.
• Real-World Example: Think of a centipede or an earthworm each segment may contain repeated structures like nerves or muscles.

Evolution of Sensory Organs

• Basic senses: vision, smell, taste, touch, hearing.
• Specialized senses: detect magnetic fields, pressure, or electric fields.
• Definition: Cephalization concentration of sensory organs in the head.
• Real-World Example: Sea turtles use Earth’s magnetic field to navigate long migrations.

Diversification of Sensory Organs

• Sight: Flies use compound eyes to find food, mates, and escape predators. Stimulus: light
• Hearing: Bats use hearing to find prey and avoid obstacles in the dark. Stimulus: sound
• Taste/smell: Some male moths have elaborate antennae to detect chemical signals. Stimulus: molecules
• Touch: Sea anemones detect and capture prey using touch. Stimulus: contact, pressure
• Other senses:
  • Pit vipers: detect temperature (thermal energy).
  • Sea turtles: detect magnetic fields.
  • Sharks: detect electric fields.
  • Birds: detect barometric pressure.
  • Comb jellies: detect gravity.

Animal Feeding Strategies

• What they eat:
  • Detritivores: Feed on dead organic matter.
  • Herbivores: Feed on plants or algae.
  • Carnivores: Feed on other animals.
  • Omnivores: Eat both plants and animals.
• How they eat:
  • Suspension feeders, deposit feeders, fluid feeders, mass feeders.
• Real-World Connection: Baleen whales are suspension feeders, filtering tons of krill from ocean water daily.

Diversification of Ecological Roles

• Detritivores: Feed on dead organic matter. Example: Millipedes feed on decaying leaves.
• Herbivores: Feed on plants or algae. Example: Pandas eat bamboo.
• Carnivores: Feed on animals. Example: Owls hunt and consume prey.
• Omnivores: Feed on plants, animals, fungi, protists, archaea, and/or bacteria. Example: Humans.

Special Ecological Roles

• Parasites harvest nutrients from parts of their hosts.
  • Usually smaller than victims.
  • Endoparasites live inside hosts and have simple, wormlike bodies.
  • Ectoparasites live outside hosts and have limbs or mouthparts to grasp the host.
• Question: Are parasites carnivores? No!
• An organism that feeds on a host without immediately killing it; often lives in or on the host.

Movement Strategies

• Movement functions: find food, escape, reproduce, disperse.
• Skeletons:
  • Hydrostatic: e.g., earthworms: support from flexible body wall in tension surrounding fluid or soft tissue under compression.
  • Endoskeleton: e.g., humans bones and spicules in sponges: derive support from rigid structures inside the body.
  • Exoskeleton: e.g., insects such as the external armor of arthropods: derive support from rigid structures on the outside of the body.
• Real-World Connection: Think about how a jellyfish pulses (hydrostatic) versus how your bones support your frame (endoskeleton).

Diversification of Limbs

• Lobe-like limbs: Onychophorans (velvet worms) use lobe-like limbs to crawl.
• Jointed limbs: Arthropods (crabs) and vertebrates use jointed limbs for locomotion and feeding.
• Parapodia: Polychaete worms use bristled parapodia to crawl and swim.
• Tube feet: Echinoderms like sea stars use tube feet to crawl.
• Arms and tentacles: Octopuses use muscular tentacles to crawl, swim, and grab prey.

Embryo Development

• Oviparous: eggs laid outside (e.g., birds).
• Viviparous: live birth (e.g., mammals).
• Ovoviviparous: eggs hatch inside the body (e.g., some sharks).
• Seahorses are ovoviviparous, but the males carry the eggs!

Metamorphosis and Animal Life Cycles

• Most sexually reproducing animals have diploid-dominant life cycles.
• Most animals go through multiple stages from birth to adulthood.
• Some develop directly (juveniles resemble adults).
• Others develop indirectly, involving a major transformation.

Metamorphosis Details

• Metamorphosis = a dramatic transformation from one developmental stage to another.
• Common in animals with indirect development:
  • Larva: immature, looks different from adult.
  • Juvenile: looks like adult, but not sexually mature.
  • Adult: reproductive stage.

Importance of Metamorphosis

• Reduces competition between life stages:
  • Larvae and adults often eat different foods.
  • Live in different environments.
• Increases chances of survival and niche specialization.
• Real-World Example: Frogs
  • Tadpole (larva): Lives in water, breathes through gills, eats algae.
  • Adult frog: Lives on land, breathes air, eats insects.
  • This separation in diet and habitat reduces resource competition between stages.