life in the sea

Introduction to Chordates

  • Discussion of two invertebrate groups of chordates
  • Overview of marine reptiles, sharks, fishes, and marine mammals
  • Importance of Phylum Chordata
  • Structurally diverse organisms in the same phylum as humans and other vertebrates

Characteristics of Chordates

  • Fundamental characteristics of chordates:

    • Notochord: a flexible rod running along the dorsal length, tough yet pliable.
    • Dorsal Hollow Nerve Cord: associated with the nervous system, located along the back
    • Pharyngeal Slits: structures for gas exchange, typically observed when discussing gills.
    • Cephalization: localization of sensory organs at the head of the organism, which provides an evolutionary advantage for sensing surroundings.
    • Post-anal Tail: evolutionary trait often observed in the life cycle, though not all adult chordates retain this trait.

  • The requirement of these characteristics on some level during the life cycle (from fertilization to death):

    • Example: Humans exhibit the notochord during embryonic development which later forms the backbone.

Organization of Chordates

  • Classification of chordates focuses on two invertebrate subphyla:
    • Urochordates (e.g., tunicates or sea squirts)
    • Cephalochordates (e.g., lancelets)
  • Moving on to the vertebrate subphyla that possess backbones, including agnathans, cartilaginous, and bony fishes, amphibians, reptiles, and mammals.

Urochordates (Tunicates/Sea Squirts)

  • Focus on the class Ascidiacea within Urochordates.
  • Adults are sessile filter feeders, displaying bright colors and irregular shapes.
    • Larval Stage: Characteristics include notochord, dorsal hollow nerve cord, and pharyngeal slits.
    • Larval tunicates are planktonic and exhibit clear cephalization.
  • Adult Tunicates:
    • Have a tunic (an outer covering).
    • Water entry through the buccal siphon (mouth) and exits through the atrial siphon (excurrent).
    • Possess a pharyngeal basket that filters particles from the water, aided by an endostyle that produces mucus to trap food. Digestive structures include a stomach, intestines, and anus (complete digestive tract).

Importance and Applications of Tunicates

  • Tunicates are significant for bioremediation due to their ability to filter bacteria from water.
  • Research into pharmaceutical properties includes the extraction of antibacterial compounds like 'stylla'.

Cephalochordates (Lancelets)

  • Common name: Lancelets
    • Small, burrowing organisms found in marine environments.
    • Displaying clear morphological characteristics such as pharyngeal slits, notochord, and dorsal hollow nerve cord.
  • Filter feeding behavior in sandy environments and basic physiological structures including an open circulatory system and dioecious reproductive system.

Marine Reptiles Overview

  • The transition to vertebrate discussion involving marine reptiles, focusing on three orders:
    • Order Squamata (includes sea snakes and iguanas)
    • Order Testudines (focus on sea turtles)
    • Order Crocodilia (emphasis on marine crocodiles and alligators)

Order Squamata (Sea Snakes)

  • Contains approximately 62 species (true sea snakes).
    • Found primarily in the Indian and Pacific Oceans, occasionally seen in regions affected by El Niño phenomena.
  • Notable adaptations:
    • Compressed tail for swimming agility.
    • Nostril flaps to prevent water intake while diving.
    • Highly toxic neurotoxin venom to subdue prey.

Order Testudines (Turtles)

  • Focus on sea turtles but also includes other freshwater species.

Order Crocodilia (Crocodiles and Alligators)

  • Unique ecological dynamics in South Florida where both crocs and gators coexist

Marine Iguanas Overview

  • Only one species, found exclusively in the Galapagos Islands (endemic).
  • Exhibit adaptations for feeding on algae in the marine environment.
  • Morphological features that assist in their semi-aquatic lifestyle include specialized noses and the ability to excrete excess salt.

Conclusion and Class Wrap Up

  • Emphasis on the roadmap for upcoming classes covering vertebrate features and roles in ecosystems.