Animals

Animals: Protostomes

General Characteristics

  • Bilaterally symmetrical, triploblastic, spiral cleavage.

  • Blastula develops into the mouth.

  • Key adaptations: Cephalization, CNS, coelom, tube-within-a-tube body plan.

Major Lineages

  1. Lophotrochozoa: Includes Platyhelminthes, Annelida, Mollusca.

    • Platyhelminthes: Flatworms, mostly parasitic, lack coelom, reproduce sexually and asexually.

    • Annelida: Segmented worms, closed circulatory system, includes earthworms and leeches.

    • Mollusca: Soft-bodied, diverse (e.g., snails, octopus), open/closed circulatory systems.

  2. Ecdysozoa: Includes Nematoda and Arthropoda.

    • Nematoda: Roundworms, cuticle molted, pseudocoelom, parasitic and free-living.

    • Arthropoda: Includes insects, crustaceans, and spiders. Segmented body, exoskeleton, open circulatory system.

Animals: Deuterostomes

General Characteristics

  • Radial cleavage, enterocoelom, anus develops first.

  • Key phyla: Echinodermata, Hemichordata, Chordata.

Major Lineages

  1. Echinodermata: Sea stars, sea urchins; radial symmetry in adults, water vascular system for movement.

  2. Hemichordata: Acorn worms; gill slits, dorsal nerve cord, close relation to chordates.

  3. Chordata:

    • Key Features: Notochord, dorsal nerve cord, pharyngeal slits, post-anal tail.

    • Subphyla:

      • Cephalochordata: Lancelets, burrowers with notochord.

      • Urochordata: Tunicates, sessile adults with a gelatinous tunic.

      • Vertebrata: Vertebrates, internal skeleton, closed circulatory system.

Vertebrate Evolution

  • Innovations: Jaws, bony skeleton, limbs for land, amniotic egg.

  • Classes include:

    • Fish: Jawless (hagfish, lampreys), cartilaginous (sharks), bony (ray-finned, lobe-finned).

    • Amphibians: Water-dependent reproduction, skin respiration.

    • Reptiles: Amniotic egg, keratinized scales.

    • Birds: Flight adaptations, feathers, hollow bones.

    • Mammals: Hair, mammary glands, differentiated teeth, viviparous (marsupials, placentals).

Animals: Overview

  • ~1.3 million species described.

  • Characteristics:

    • Eukaryotic, multicellular, heterotrophic.

    • Lack cell walls; cells held by extracellular proteins and junctions.

    • Excitable tissues (muscle, nerve).

  • Life stages involve blastulation and gastrulation to form digestive cavities.

Origins and Body Plans

  • Origin:

    • Evolved from colonial flagellated protists (Precambrian).

    • Specialized cells formed a double-layered "sac-within-a-sac" body plan.

  • Body plans:

    • Key traits for classification: symmetry, tissues, body cavities, embryonic development.

Key Features to Classify Animals

Body Symmetry

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

  • Radial symmetry:

    • Body parts arranged around a central axis (e.g., jellyfish, sea anemones).

    • Suited for sedentary or free-floating lifestyles.

  • Bilateral symmetry:

    • Divided into mirror-image halves; has anterior/posterior and dorsal/ventral regions.

    • Associated with mobility and cephalization (concentration of sensory organs at the head).

Tissue Development

  • Diploblastic (basal phyla): Two germ layers (ectoderm and endoderm).

  • Triploblastic (bilaterians): Three germ layers (ectoderm, mesoderm, endoderm).

    • Ectoderm: Nervous system, external coverings.

    • Mesoderm: Muscles, most internal organs.

    • Endoderm: Gut lining, respiratory organs.

Body Cavities

  • Types:

    • Acoelomate: No body cavity (e.g., flatworms).

    • Pseudocoelomate: Partially lined body cavity.

    • Coelomate: Fully lined body cavity.

  • Functions:

    • Nutrient transport, egg/sperm development, organ space, hydrostatic skeleton.

Patterns of Embryonic Development

  • Bilaterians split into:

    • Protostomes:

      • Spiral, determinate cleavage.

      • Blastopore forms mouth; mesoderm forms by splitting (schizocoelom).

    • Deuterostomes:

      • Radial, indeterminate cleavage.

      • Blastopore forms anus; mesoderm forms by outpocketing (enterocoelom).

Basal Phyla

Porifera (Sponges)

  • ~8,000 species, mostly marine.

  • Body plan:

    • Asymmetrical, suspension feeders.

    • Key cells:

      • Choanocytes: Create water flow, trap food.

      • Amoeboid cells: Digest and transport nutrients.

      • Porocytes: Regulate pore diameter.

    • Water enters through pores, flows out via osculum.

  • Reproduction:

    • Sexual (hermaphrodites) or asexual (budding, fragmentation).

Ctenophora (Comb Jellies)

  • Gelatinous body with 8 rows of ciliary "combs" for propulsion.

  • Carnivorous, using sticky cells for prey capture.

  • Have a through-gut with anal pores.

Cnidaria

  • Includes hydras, jellyfish, corals, anemones (~10,000 species).

  • Body forms:

    • Polyp: Sessile, vase-shaped.

    • Medusa: Free-swimming, bell-shaped.

  • Body plan:

    • Radial symmetry; gastrovascular cavity with one opening.

    • Tentacles equipped with cnidocytes containing nematocysts (stinging cells).

  • Classes:

    • Anthozoa: Corals, sea anemones (no medusa stage).

    • Hydrozoa: Colonial forms (e.g., Hydra, Portuguese man-of-war).

    • Scyphozoa: True jellyfish; medusa stage dominant.

    • Cubozoa: Box jellies with venomous tentacles.

    • Staurozoa: Stalked jellyfish with attached medusa.

Placozoa

  • Simplest animal structure; reproduce asexually by division.

  • Absorb nutrients by secreting digestive enzymes over food particles.

Acoelomorpha

  • Small flatworms (bilaterians), unsegmented, ciliated.

  • Lack coelom, circulatory, and excretory systems.

  • Simple nervous system with parallel nerve cords.