BIO201 Arthropods Notes

Ecdysozoans

  • Definition: Ecdysozoans are also known as molting animals.

  • Cuticle:

    • Definition: A nonliving covering produced by the epidermis.

    • Functions:

    • Support: Provides structure to the organism.

    • Protection: Shields against environmental threats.

  • Growth Mechanism:

    • Growth in ecdysozoans requires molting, where the organism sheds its cuticle to grow.

  • Evolutionary Insight:

    • Genetic data suggests that the capacity for molting evolved only once among these animals.

Phylum: Arthropoda

  • General Information:

    • The largest and most diverse phylum within the animal kingdom.

    • Common examples include insects, arachnids, and crustaceans.

Arthropod Secrets to Success

  • Extreme Tagmatization:

    • The segmentation of body regions into specialized tagmata (e.g., head, thorax, abdomen).

  • Exoskeleton:

    • Definition: A skeleton that is located outside of the body, typically made of chitin and sometimes calcified.

    • Movement: Muscles work against the exoskeleton to enable movement.

    • Internal Space Utilization: Frees up internal space, no longer acting as a hydrostatic skeleton.

    • Protection and Cost: While providing considerable protection to the organism, it requires molting for growth.

  • Jointed Appendages:

    • Description: Segmented limbs that provide versatility for various functions including feeding, defense, locomotion, and reproduction.

  • Flight (Selective):

    • Not all arthropods are capable of flight, but those that can utilize it for dispersal and accessing resources.

Exoskeleton and Cuticle Characteristics

  • Cuticle Composition:

    • Varies with environment:

    • Lightweight: Chitin

    • Heavier: Calcified options.

  • Growth Implication:

    • Must molt to grow, representing an energetic investment and risk due to vulnerability during this phase.

Adaptations for Gas Exchange

  • Mechanisms for Gas Exchange:

    • Aquatic, semi-aquatic, and terrestrial arthropods utilize adaptations such as:

    • Gills (e.g., book gills, book lungs)

    • Trachea system for terrestrial environments

    • Note: The barrier for gas exchange is not completely impermeable; adaptations evolve based on habitat constraints.

Internal Circulatory Structures

  • Anatomy Overview:

    • Efficient use of internal space:

    • Hemolymph circulates within sinus cavities surrounding organs.

    • Contains a tubular heart with ostia to regulate circulation.

Phylum: Arthropoda Subgroups

  1. Chelicerata

    • Examples: Spiders, scorpions, ticks, mites, horseshoe crabs.

    • Body Structure: Consists of 2 body segments (tagmata):

    • Cephalothorax: The combined head and thorax region.

    • Abdomen: The posterior region containing reproductive organs and digestive tract.

Chelicerata Appendages

  • Chelicerae:

    • Definition: The first set of appendages adapted for feeding, typically pincers or fangs.

  • Pedipalps:

    • Definition: The second set of appendages used for feeding, defense, and mating.

  • Respiration:

    • Mechanisms include book gills, book lungs, or trachea; chelicerates lack antennae.

Chelicerate Diversity

  • Notable Examples:

    • A. Horseshoe crabs

    • B. Sea Spiders

    • C. Mites

    • D. Ticks

    • E. Spiders

    • F. Scorpions

    • G. Daddy Longlegs

    • H. Vinageroon

Myriopoda

  • Defining Characteristics:

    • Organisms with many legs; main representatives include millipedes and centipedes.

  • Millipedes:

    • Primarily detritivores, possessing two pairs of legs per body segment.

    • Definition: Contrary to their name, they do not have 1000 legs.

  • Centipedes:

    • Active hunters typically prey on insects, characterized by one pair of legs per body segment and a venomous bite.

Crustacea

  • General Characteristics:

    • Composed of a mineralized tough cuticle; majority are aquatic.

  • Common Examples:

    • Species including crayfish, crabs, isopods, amphipods, copepods, krill, barnacles, and others.

Notable Crustaceans

  • Familiar Crustaceans:

    • Decapoda (e.g., crabs and shrimps)

  • Advanced Knowledge of Crustaceans:

    • Stomatopods: Known as Mantis Shrimp (not a true shrimp), renowned for their punch strength.

    • Coconut Crab: A terrestrial crustacean known for its size and unique adaptations.

Insects

  • Diversity Statistics:

    • Approximately 1 million species described, >50% of all described species.

    • Inhabit various ecosystems: terrestrial, freshwater, and a few marine species.

  • Body Structure:

    • Typical anatomy includes three body segments and six walking legs.

  • Reproductive and Life Cycle Characteristics:

    • Many insects exhibit complex life cycles that may include metamorphosis, either complete (holometabolous) or incomplete.

Secrets to Insect Success

  • Adaptations Include:

    • Resistance to desiccation through:

    • Cuticle: Acts as a barrier.

    • Spiracles and Trachea: Allow for gas exchange despite body coverage.

    • Ability to Fly: Provides advantage for food access and habitat exploration.

    • Metamorphic Development: Holometabolous development enhances adaptability through distinct life stages.

Fly Structure in Insects

  • Importance of Flight:

    • Facilitates access to new food sources and habitats, while also enabling effective predator avoidance.

Conclusion

  • The diversity and success of these phyla highlight the remarkable adaptations of arthropods and their evolutionary strategies, explaining the extensive number of insect species observed today.