Lecture 3.5 - Invertebrates and Introduction to Deuterostomes

Subphylum Hexapoda (Insects)

• Definition: Hexapoda means "six-footed"; these are insects.
• Characteristics:
  • Largest subphylum within Arthropoda.
  • Three tagmata: head, thorax, abdomen.
  • Many have wings, which is key to their success and diversity.
  • Diverse mouthparts adapted for various feeding strategies (e.g., bees, grasshoppers, mosquitoes).
• Metamorphosis:
  • Complete (e.g., butterflies): larva -> pupa -> adult.
  • Incomplete (e.g., grasshoppers): progressive molts to reach adult form.

Completion of Protostomes

• Finished discussing Arthropods and Protostomia.
• Protostomes: mouth develops first in embryonic development.

Introduction to Deuterostomes

• Definition: Anus develops first in embryonic development.
• Groups: Echinodermata and Chordata.

Phylum Echinodermata

• Examples: Sea stars, brittle stars, sea urchins, sea cucumbers.
• Characteristics:
  • Marine only; all are saltwater species.
  • Coelomates, with a coelom evolved independently from other groups.
  • Penta-radial symmetry as adults, bilateral symmetry as larvae.
  • Anatomy:
    • Organ systems radiate from a central ring into arms.
    • Capable of regeneration from detached arms.
  • Endoskeleton: Made of calcium carbonate.
  • Water Vascular System:
    • Unique to echinoderms.
    • Hydraulic pressure for tube feet movement (locomotion, prey manipulation).
    • Functions as a circulatory system.

Phylum Chordata

• Characteristics:
  • All have five key features at some stage:
    1. Notochord
    2. Dorsal hollow nerve cord
    3. Pharyngeal slits
    4. Endostyle
    5. Post-anal tail
• Closed circulatory system.

Subphylum Cephalochordata

• Known as lancelets.
• Filter feeders, retain all chordate features throughout life.

Subphylum Urochordata

• Known as tunicates.
• Larvae have chordate features; adults lose most features.
• Filter feeders, some are sessile, some form colonies.

Vertebrates (Subphylum Vertebrata / Craniata)

• Key Evolutionary Innovations:
  • First innovation: skull to protect the brain.
  • Vertebral column replaces the notochord.
• Fish: Paraphyletic group, mostly ectotherms.

Hagfish

• Limbless scavengers.
• Have a skull but no vertebrae.

Lampreys

• Have both skull and vertebrae, no jaws.
• Parasites or filter feeders.

Gnathostomata (Jawed Vertebrates)

• Includes all jawed vertebrates.

Class Chondrichthyes

• Sharks, rays, and skates (cartilaginous fishes).
• Characteristics:
  • Cartilaginous skeleton.
  • Paired fins.
  • Most are obligate ram ventilators, needing constant movement.

Clade Osteichthyes (Bony Fishes)

• Characteristics:
  • Bone skeletons.
  • Swim bladder for buoyancy.
  • Operculum to cover gills.
• Classes:
  • Actinopterygii: Ray-finned fishes.
  • Sarcopterygii: Lobe-finned fishes, precursors to terrestrial vertebrates.