Animal Development and Diversity

Stages of Life

  • Three stages discussed: Zygote, Gammie, Adult.

Differentiation in Life Forms

  • Body Directions: Focus on parts of the body rather than just location.

  • Tail and Anus: Important distinctions in developmental terminology.

Protostomes vs. Deuterostomes

  • Primary Differences:

    • Cleavage Type:

    • Protostomes: Spiral cleavage.

    • Deuterostomes: Radial cleavage.

    • Developmental Fate:

    • Protostomes: Determinate development.

    • Deuterostomes: Indeterminate development.

    • Symmetry:

    • Both protostomes and deuterostomes exhibit bilateral symmetry in adulthood.

Basal Taxa in Animal Phylogeny

  • Sponges: Represent the basal lineage of the animal kingdom.

  • Cnidarians: First derived group after sponges.

    • Characteristics:

    • Only truly radially symmetric animals.

    • Lacking a head; instead utilize a nerve net for sensory functions.

Defining ‘Head’ in Bilateral Animals

  • Definition of a head: Area at the anterior end where sensory and nerve information accumulates.

  • Implications: No requirement for a recognizable structure or classic brain.

Lophophores and Ectysozoans

  • Invertebrate Characteristics:

    • Unified by presence of lophophores—hair-like structures utilized at some point in life cycles.

    • Lophophores can be cilia or larger structures resembling fingers.

  • Trochophore Larvae: A larval stage equipped with a crown of cilia used for movement.

Ectysozoa Characteristics

  • Cuticle: Present in all eptizoans; different from exoskeletons used by arthropods.

    • Definition: A protective layer that is shed, not to be confused with a skeleton.

Diversity and Evolution in Animals

  • Key survival traits across the animal kingdom:

    • Variations in reproduction, development, mobility, feeding, and defense mechanisms.

Phylogenetic Trees as Hypotheses

  • Phylogenetic trees represent hypotheses about evolutionary relationships among taxa.

  • Importance of being able to recognize key characteristics such as lophophores on these trees.

Group Discussions and Presentation Structure

  • Slides on Lophophores: Emphasizes filling in critical information collectively.

  • Groups: Discuss platforms (planarians) and how they utilize lophophores for feeding.

    • Unique feeding structure—mouth hole serves multifunctional purposes (mouth, anus, reproductive).

Specific Invertebrate Examples

  • Flatworms:

    • Lack circulatory systems; depend on high surface area for gas exchange.

  • Lamp Shells (Brachiopoda):

    • Use large anchor foot for substrate attachment; lophophores for feeding.

  • Rhizomes: Recently discovered as potential deuterostomes despite previously being classified differently due to unique developmental patterns.

Segmented Worms (Annelids)

  • Characteristics:

    • Segmentation allows customization of body plans; important for evolutionary adaptations.

    • Use skin for gas exchange without a central organ like a heart; blood distributed through muscular contractions of segments.

Mollusks

  • Body Structure:

    • Possess a muscular foot for locomotion and a radula for feeding.

    • Vulnerable larvae ensure high susceptibility to climate change due to calcification needs.

    • High Intelligence: Especially among cephalopods like octopuses, known for complex nervous systems and ability to respond to various stimuli.

Ecdysis and Ecdysozoa Characteristics

  • Molting: Essential for growth but creates vulnerability during the process.

  • Protective Coating: Varies significantly among taxa (e.g., lorica in lorisifera).

    • Velvet Worms: Have a modest cuticle, offering limited protection.

    • Tardigrades: Known for extremophilic characteristics, thriving in diverse and extreme environments, capable of surviving extreme conditions (dry, wet, hot).