Arthropods and Crustaceans

Arthropods: Introduction

  • Arthropods are the largest animal group, with approximately 1.2 to 1.5 million described species.
  • The lecture will focus on Crustacea, a subphylum within Arthropoda.
  • There are 4 subphyla within the phylum Arthropoda.

Crustacea

  • Crustaceans include crayfish, lobsters, and shrimp.
  • Crustacea is the second largest subphylum within Arthropoda.
  • The largest subphylum is Hexapoda, which includes insects.

Hexapoda

  • Hexapoda is the largest subphylum, characterized by having six legs.
  • The subgroup within Hexapoda called Insecta is the most diverse.
  • There are many orders of insects, with beetles being particularly numerous.

Jointed Appendages (Arthropoda Characteristics)

  • Arthropods are characterized by jointed appendages, which include legs, antennae, and claws.
  • "Arthro" means joint, as in arthritis.
  • Jointed appendages allow for bendable and versatile movement.

Exoskeleton

  • Arthropods have an exoskeleton, which is different from the shell of mollusks.
  • The exoskeleton provides protection, similar to a shell.
  • Unlike a shell, the exoskeleton is shed or molted as the arthropod grows.
  • Muscles are attached to the inside of the exoskeleton, allowing for movement.

Composition of Exoskeleton

  • The exoskeleton is made of chitin, a keratin-like complex carbohydrate (sugar).
  • Arthropods must shed their exoskeleton to grow.
  • Human bone growth plates typically close around the age of 14-19, ceasing further growth.

Other Arthropod Subphyla

  • Besides Crustacea and Hexapoda, other subphyla include:
    • Spiders, scorpions, daddy long legs, ticks, and mites (belonging to the group with eight legs).

Marine Examples

  • Sea spiders are a marine example within the spider/scorpion subphylum.
  • Horseshoe crabs are another ancient marine animal with an exoskeleton.

Myriapoda

  • Millipedes and centipedes belong to another subphylum.

Tagmata (Body Segments)

  • Arthropod bodies are divided into tagmata (segments).
  • Crustaceans (e.g., lobsters) have two tagmata: the cephalothorax (head and thorax fused) and the abdomen.
  • Insects have three tagmata: the head, thorax, and abdomen.

Additional Notes

  • House dust is composed of keratin from dead skin, hair, and dirt.
  • Space dust is also present in house dust.

Video: Terrestrial vs. Aquatic Arthropods

  • The videos contrast terrestrial (land-dwelling) arthropods with aquatic (water-dwelling) crustaceans.

Copapods

  • Copepods are the most dominant arthropod in terms of numbers.
  • Hexapods are the most diverse in terms of species.
  • Arthropods have invaded many environments due to their adaptability.

Arthropod Adaptations

  • Jointed legs provide stability and shock absorption.
  • Appendages like antennae serve as onboard sensors.
  • Arthropods exhibit a Swiss Army knife design with variations in appendages for different functions.
  • The arthropod body plan is segmented with legs adapted for various purposes.
  • A walking leg can evolve into a grasping claw.
  • The tail of a lobster can be tucked underneath to form a sand-burrowing crab.

Exoskeleton as Body Armor

  • The exoskeleton serves as support and armor.
  • Arthropods molt to grow, shedding their old exoskeleton.
  • During molting, a soft new skeleton develops beneath the old one.
  • Softshell crabs are crabs that have just molted and are entirely edible.
  • After molting, the new exoskeleton hardens over a couple of days.
  • Molting occurs in various arthropods, including insects and mites.
  • A 50-year-old lobster may have molted hundreds of times.

Arthropod Feeding

  • Arthropods are versatile eaters with specialized mouth appendages.
  • Some appendages help with eating, while others aid in breathing by sweeping water across the gills.

Evolutionary History

  • Arthropods thrived during a period of explosive diversification.
  • They have survived through time due to their adaptations.
  • Crabs prosper in extreme environments like deep ocean trenches.

Horseshoe Crabs

  • Horseshoe crabs are living fossils.
  • They mate in the water but lay their eggs on land.
  • Their eggs develop on land protected by moist sand.

Conquest of Land and Air

  • Arthropods were among the first creatures to leave the sea and colonize land.
  • They developed tools for survival on land and eventually took to the air.

Summary

  • Arthropods dominated the oceans and were the first animals to crawl onto land.
  • They also were the first organisms to fly.

Miscellaneous

  • Echinoderms (e.g., starfish) have spiny skin ("echino" means spiny, "derma" means skin).