Ecdysozoa and Arthropods Overview

Lobster Industry

• Declining Catch: U.S. lobster catch is decreasing due to environmental and economic challenges driven by climate change.
• Migration: Warmer waters cause lobsters to migrate from traditional fishing grounds.

Learning Objectives

• Superphylum Ecdysozoa: Understand characteristics and significance.
• Nematodes: Analyze their ecological roles and health impacts.
• Arthropoda: Study structure, nutrition, and reproductive systems.
• Insect Metamorphosis: Describe the processes involved in insect development.

Phylogenetic Tree of Animals

• Classification from Metazoa to specialized groups:
  • Eumetazoa: Organisms with specialized tissues.
  • Bilateria: Animals with bilateral symmetry and three germ layers (triploblastic).
  • Ecdysozoa: Includes organisms that undergo molting.
  • Major Phyla: Include Arthropoda, Nematoda, Platyhelminthes, etc.

Superphylum Ecdysozoa

• Definition: Named for the process of ecdysis, or molting.
• Physical Characteristics:
  • Cuticle offers support and protection.
  • Internal fertilization through amoeboid sperm to adapt to dry environments.
• Diversity: 8 major phyla, notably Nematodes and Arthropods as the most common.

Nematodes (Roundworms)

• Diversity: Over 20,000 species documented, e.g., $C. elegans$ (1 mm).
• Ecological Role: Predators or saprophytes, essential in soil ecosystems.
• Model Organism: $C. elegans$ used in genetics and neurobiology studies.

Parasitic Nematodes

• Common Species:
  • Ascaris lumbricoides: Human intestinal parasite, segmented; infects through ingestion of eggs.
  • Hookworm: Infects humans via skin contact; affects over 500 million individuals globally.
• Transmission and Lifecycle:
  • Larval stages penetrate skin, affecting lungs and intestines.

Common Parasitic Nematodes and Their Lifecycle**

• Infection Routes:
  • Hookworm: Juveniles through soil; suck blood from intestines.
  • Pinworm: Contaminated surfaces, most common in U.S. children.
  • Trichina worm: Through infected food, occasional human infections.
• Disease Examples: River blindness, Guinea worm disease, Elephantiasis.

Phylum Tardigrada (Water Bears)

• Characteristics:
  • Tiny (0.3-0.5 mm), reside in moist environments.
  • Unique morphology with four pairs of stubby legs.
  • Capable of cryptobiosis, surviving extreme conditions.

Phylum Arthropoda (Arthropods)

• Diversity: Accounts for 85% of known species with jointed appendages (legs and mouthparts).
• Body Structure:
  • Segmentation into head, thorax, abdomen.
  • Rigid exoskeleton molted as the organism grows.
  • Open circulatory system and sophisticated nervous system.

Major Subphyla of Arthropoda

• Crustacea: Includes shrimp, lobsters, crabs, characterized by gills and antennates.
• Chelicerata: Features spiders and scorpions, with specialized mouthparts (chelicerae).
• Myriapoda: Includes centipedes (carnivorous) and millipedes (herbivorous).
• Hexapoda: Insects characterized by three pairs of legs and wings.

Insect Metamorphosis

• Types:
  • Ametabolous: No metamorphosis, simple growth.
  • Hemimetabolous: Gradual change from nymph to adult.
  • Holometabolous: Complete metamorphosis (egg, larva, pupa to adult).
• Implications: Development strategies influence survival and adaptation to environments.