Animals & Lophotrochozoans Notes

What Are Animals?

  • Multicellular eukaryotes.
  • Heterotrophs that ingest food.
  • Animal phyla are characterized by body plan arrangements (body symmetry, embryonic tissue layers, presence/absence of body cavity, and early embryonic development).
  • Animals within the same phylum can vary and inhabit diverse habitats.

Body Symmetry

  • Asymmetry: No plane of symmetry (e.g., sponges).
  • Radial symmetry: Multiple planes of symmetry (e.g., sea anemones).
  • Bilateral symmetry: Single plane of symmetry, distinct anterior and posterior ends (e.g., lizards).

Early Embryonic Development and Germ Layers

  • Ectoderm: Gives rise to skin and nervous system.
  • Mesoderm: Becomes muscles, connective tissue, skeleton, kidneys, circulatory and reproductive organs.
  • Endoderm: Forms the lining of the gut and major organs derived from it.

Animal Body Plans and Cavities

  • Acoelomate: No coelom, only a digestive cavity.
  • Pseudocoelomate: "Sort of" body cavity (pseudocoelom) between mesoderm and endoderm.
  • Eucoelomate: True body cavity (coelom).

Gametes and Fertilization

  • Gametes (sperm and egg) produced in gonads through meiosis.
  • Fertilization: Egg (n) + sperm (n) unite à diploid zygote (2n).
  • nn = one set of chromosomes.
  • 2n2n = two sets of chromosomes.
  • Fertilization membrane prevents multiple sperm from fertilizing the egg.

Internal vs. External Fertilization

  • Internal Fertilization: Eggs and sperm meet inside the body; females invest more energy per egg.
  • External Fertilization: Eggs and sperm dispersed into the environment; gametes are vulnerable, energy invested in producing many gametes.

Animal Classification

  • Sponges and cnidarians are among the earliest animals.
  • Remaining phyla are grouped into protostomes and deuterostomes based on embryonic development.

Porifera (Sponges)

  • Lack distinct body plan, tissues, organs, and organ systems.
  • Sessile filter feeders.
  • Water enters through ostium (pores) and exits through osculum (large opening).
  • Choanocytes (collar cells) create water current.
  • Spicules provide structural support.

Cnidaria (Coral, Jellyfish, Sea Anemones)

  • Radial symmetry, diploblastic (2 tissue layers: ectoderm and endoderm).
  • Possess muscle and nerve tissue.
  • Have cnidocytes (stinging cells) on tentacles to capture prey.
  • Body plan variations: sessile polyp and motile medusa.

Protostomes

  • Undergo protostome embryonic development.
  • Bilateral symmetry and cephalization (concentration of nervous system at the head).
  • Triploblastic (three tissue layers).
  • Function through organ systems.
  • Two lineages: Lophotrochozoa and Ecdysozoa.

Protostome Lineages

  • Lophotrochozoa
  • Platyhelminthes (flatworms)
  • Annelida (earthworms, leeches)
  • Mollusca (mollusks)
  • Ecdysozoa (covered later)

Growth Patterns

  • Lophotrochozoans grow incrementally.

Platyhelminthes (Flatworms)

  • Acoelomate (lack a true body cavity).
  • Incomplete digestive system (gastrovascular cavity); tapeworms have no digestive system.
  • Three groups: free-living planarians, parasitic flukes, and parasitic tapeworms.

Annelida (Segmented Worms)

  • Eucoelomate; coelom acts as a hydrostatic skeleton.
  • Metameric (segmented) body.
  • Complete, one-way digestive tract.
  • Three groups: terrestrial earthworms, freshwater leeches, and marine polychaete worms.

Mollusca (Mollusks)

  • Eucoelomate with a complete digestive tract.
  • Many have a radula (tongue-like structure with teeth).
  • Ventral region forms a muscular foot.
  • Dorsal region forms a mantle, sometimes with a shell.
  • Four main groups: chitons, gastropods, bivalves, and cephalopods.

Earthworm Dissection Structures

  • Pharynx, hearts, seminal vesicles, seminal receptacles, esophagus, crop, gizzard, dorsal blood vessel, intestine.