life in the sea

Introduction to Arthropods

  • Arthropods are a major group of invertebrates characterized by jointed legs and segmented bodies.
  • Over a million different species of arthropods exist, inhabiting various environments:
    • Terrestrial (on land)
    • Aerial (in the air)
    • Aquatic (in water)
  • Focus on aquatic arthropods, particularly marine species.

Characteristics of Arthropods

  • All arthropods exhibit metamerism, meaning they have segmented bodies.
  • Body regions can be classified into:
    • Head
    • Cephalothorax (combination of the head and chest)
    • Abdomen
    • Telson (the tail region)
  • Exoskeleton made of chitin is a defining feature of arthropods.

Exoskeleton and Growth

  • The presence of an exoskeleton necessitates molting to permit growth.
    • Molting process:
    • Organism sheds its old exoskeleton to grow a new, larger one.
    • Vulnerability period when the new exoskeleton is soft (e.g., soft-shell crabs).
    • Eventually, the new exoskeleton hardens, allowing the organism to expand.

Specific Groups of Arthropods

Chelicerates

  • A group including spiders and scorpions, characterized by:
    • Lack of antennae.
    • Body parts include:
    • Carapace (top shell)
    • Cephalothorax
    • Abdomen
  • Example: Horseshoe crabs (genus Limulus):
    • Ten pairs of appendages including:
    • Walking legs
    • Gills
    • Eyes
    • Blood contains a substance called LAL (Limulus Amebocyte Lysate) used in pharmaceuticals to detect bacterial contamination.
  • Ethical implications regarding the use of horseshoe crabs in medical testing.

Crustaceans

  • Diverse aquatic arthropods typically recognized by:
    • Two pairs of antennae.
    • Sexual dimorphism in male and female appearances.
    • Lifecycle begins with planktonic larvae.
Major Groups of Crustaceans

  1. Copepods

    • Class Copepoda, over 40,000 species with notable diversity.
    • Primarily planktonic with some being parasitic.
    • Serve as vital components of the marine food web (food source for larger animals).

  2. Barnacles

    • Begin as plankton before settling permanently as sessile adults.
    • Use strong adhesive secreted for attachment; unique reproductive methods through direct fertilization of neighbors.
    • Influence on ecological relationships and potential discomfort for host organisms (e.g., whales) when attached.

  3. Mantis Shrimp

    • Known for powerful, rapid-claw strikes, capable of breaking aquarium glass.
    • Possess vibrant colors and unique eye structure enabling rapid change of coloration.

  4. True Krill

    • Members of the order Euphausiacea, crucial for marine food chains.
    • Exist in large swarms; serve as primary food for baleen whales among other large predators.

  5. Decapods

    • Include shrimps, crabs, and lobsters.
    • About 10,000 species found in diverse habitats.
    • Important for culinary use and local economies (lobster season).
    • Notable examples include:
      • Florida Lobster (Panulirus argus) has reduced claws.
      • Maine Lobster (Homarus americanus) with pronounced claws.
Miscellaneous Crustacean Types
  • Mysids: Small shrimp-like organisms, often found in schools.
  • Isopods: Flattened body structure (dorso-ventrally depressed), e.g., Rolly-pollies.
  • Amphipods: Laterally compressed organisms, often found in underwater vegetation.

Ecological Importance of Arthropods

  • Arthropods play crucial roles in various ecosystems, providing essential services such as:
    • Food source for larger species (e.g., fish, birds).
    • Contribution to the cycling of nutrients in ecosystems.
  • Vast diversity among arthropods and their ecological significance allude to their evolutionary success.

Conclusion and Transition

  • Overview provides foundational knowledge of arthropods, emphasizing unique adaptations.
  • Segue into next topic of mollusks post-Easter week.
  • Engage students to stay current with materials and prepare questions for review sessions leading into the exam.