JC BIO 2 deuterostomes

Introduction to Vertebrates

• Discussion of a marine biologist's observations leading to the discovery of chordate features.

• Mention of the embryonic development in chordates, specifying the blastopore role in becoming the anus.

General Information on Chordates

• Chordates are the most familiar animals since humans are classified as one.

• Identified three critical features of chordates:

  • Notochord:

    • A flexible structure providing support, made of collagen.

    • Helps in movement and shape change.

  • Dorsal Hollow Nerve Cord:

    • Forms the central nervous system.

    • Derived from ectoderm during embryonic development.

  • Pharyngeal Slits (Gill Slits):

    • Present in all chordates; may lead to gill structures but not always.

    • Represents a homology with hemichordates.

Characteristics of Chordates

• Segmented Body Plan:

  • Includes segmented worms and arthropods with jointed appendages.

• Closed Circulatory System:

  • Blood circulates within vessels; extensive network including capillaries.

• Diet alternation:

  • Various dietary strategies, including filter-feeding (e.g., sea squirts).

Morphology and Development of Chordates

• Example of a lancelet as a basal lineage of chordates shows chordate features.

• Detailing of embryonic development processes including structure formation in the chordate.

• Notochord Functions:

  • Support and enabling movement through the flexing of the structure.

Dorsal Hollow Nerve Cord

• Development is influenced by the notochord signaling.

• Formation process involves the ectoderm folding into a tube.

Evolutionary Innovations

• Chordate evolution shows an increase in cephalization (formation of a head with sensory organs).

• Major innovations include:

  • Development of a cranium (skull).

  • Formation of vertebrae (bony structures).

  • Evolution of jaws allowing for diverse feeding strategies.

  • Further evolution leading to limbs supported by an endoskeleton.

Evolution of Eyes

• Development of vertebrate eyes showcases stages of complexity from light detection to advanced imaging.

• Stages of eye evolution:

  • Simple light/dark detection.

  • Cup-shaped eye spots facilitating directionality.

  • Formation of lenses leading to image focus adjustment.

  • Comparison with molluskan eye evolution illustrating homoplastic characteristics (similar features in different lineages due to convergent evolution).

Zoological Innovations in Feeding

• Importance of feeding adaptations in vertebrates, tracing back to early jawless fishes.

• Jaw Evolution:

  • Jaw development from gill arches allowing for more effective prey capture.

  • Distinction between early jawed fishes and modern jawed fishes.

Basal Chordate Group (Urochordata)

• Adult features include dual openings and complex organ systems highlighting evolutionary adaptations.

• Filter-feeding method involving siphons for water intake.

• Life cycle featuring a tadpole larva stage showing chordate synapomorphies.

Fish Diversity and Feeding Strategies

• Ray-finned fishes constitute the most diverse class of fish.

• Innovations in jaw structure enhancing feeding capabilities and habitat adaptation.

• Specific adaptations of catfishes illustrating ecological success in varied freshwater environments.