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Chordate Traits

• Chordates possess several key traits at some point in their life cycle:

  • Notochord

  • Pharyngeal Slits

  • Dorsal Hollow Nerve Cord

  • Post Anal Tail (in most cases)

Notochord

• A hydrostatic, fluid-filled, fibrous cylinder.

• Incompressible, used for side-to-side movement.

• Evolution leads to improved function, eventually becoming the vertebral column in bony animals.

Pharyngeal Arches/Slits

• Openings, not gills, in primitive chordates.

• Originally used for filter feeding via mucus to trap food.

• All chordates have them; some evolve into gills later.

• As evolution continues, they become the pharynx, located at the back of the throat.

Dorsal Hollow Nerve Cord

• Ectodermal in origin.

• Forms the neural tube, used for coordination.

• Enables organisms to respond to their environment.

Post Anal Tail

• Primarily used for locomotion and balance.

• Present in all chordates at some point in their life cycle.

• It disappears in highly organized animals.

Chordate Types

Hemichordates

• All are deuterostomes.

• Possess the following:

  • Pharyngeal slits

  • Neural Crest (cord)

• Lack the following:

  • Notochord

  • Post Anal Tail

• Example: Acorn Worms

Acorn Worms

• Burrowing marine animals with three body sections:

  • Proboscis (for eating)

  • Collar (for movement)

  • Trunk (containing slits and gonads)

Urochordates

• Known as Tunicates or "sea squirts".

• Possess all four chordate characteristics.

• All urochordates are marine animals.

  • Larvae are free swimmers.

  • Adults are sessile or attached.

• Tunicates are hermaphrodites (monoecious: one house).

Cephalochordates

• Around 500 million years old.

• Lancets with a chevron body shape.

• Suspension feeders that possess all chordate characteristics.

• Evolved new features:

  • Wheel organ: facilitates increased water flow.

  • Harchek's Pit: homologous to the pituitary gland.

  • Velum: blocks large particles.

Agnatha

• Includes Lampreys and Hagfish: specialized, primitive fish without bone.

• Lampreys have hooks on the sides to attach to hosts.

• Possess teeth-like rasps for scavenging.

• Some are predators.

• Lineage Radulla in Gastropods.

• Exhibit knotting behavior (mass mating).

Jaws and Fins

Chondrichtyes

• Includes Sharks, Skates, and Rays.

• Cartilaginous fish (skeleton made of cartilage).

• Lateral Line: sensory organ.

  • Ampullae of Lorenzini: sense electrical fields.

• Development of serrated teeth.

• Tend to sink due to heavy density and must continuously swim.

• Diet consists of Seals, Crustaceans, and Fish.

Ampullae of Lorenzini

• Nerve and pore lines are distributed throughout the body but concentrated on the nose and face area.

• The pores contain a jelly-like substance called Ampullae of Lorenzini which is highly sensitive.

• Sensitive to external stimuli.

Bony Fish

Osteichthyes

• Bony fish with a vertebral skeleton made of bone (not cartilage).

• Possess a swim bladder for depth control.

  • Helps fish rise and descend in water.

  • Maintains their niche and improves life and activity.

  • Aids in crawling ashore.

• Two Types:

  • Ray-Finned: muscles are inside the body wall, resulting in thin, small fins; they flop on land.

  • Fleshy-Finned: muscles control outside body.

Amphibians

General Characteristics

• Undergo metamorphosis (aquatic larvae to terrestrial adults).

• Require moist environments for reproduction and skin hydration.

• Three Orders:

  • Anura (frogs and toads)

  • Urodela (salamanders and newts)

  • Apoda (caecilians)

Anura (Frogs and Toads)

• Lack tails as adults.

• Specialized for jumping with strong hind legs.

• External fertilization in water.

Urodela (Salamanders and Newts)

• Possess tails as adults.

• Capable of limb regeneration.

• Internal fertilization, often with elaborate courtship rituals.

Apoda (Caecilians)

• Legless and resemble snakes or worms.

• Primarily burrowing animals.

• Internal fertilization.