Lecture 34 Notes: Invertebrates - Mollusks, Annelida, and Ecdysozoa

Mollusks

Class Cephalopoda

• Includes nautiluses, cuttlefish, squid, and octopi.
• Body Structure:
  • Modified from typical mollusk body plan.
  • Shell:
    • Nautilus has an external shell.
    • Squid: internal shell called a "squid pen."
    • Cuttlefish: "cuttle bone" for buoyancy, used as a dietary supplement for birds.
  • Foot:
    • Modified into arms/tentacles for grasping.
• Circulatory System: Closed system.
• Movement: Jet propulsion by expelling water from the mantle cavity.

Class Scaphopoda

• Known as tusk or tooth shells.
• Shell: Conical, open at both ends.

Phylum Annelida

• Includes earthworms, leeches, and segmented aquatic worms.
• Body Structure:
  • Segmented body plan.
  • Closed circulatory system.
  • Coelom divided into segments by septa.
• Locomotion:
  • Terrestrial worms have setae for crawling.
  • Aquatic worms use parapodia for swimming and respiration.

Classes of Annelida

Class Polychaeta

• Known as bristle worms.
• Mostly marine aquatic species.

Class Clitellata

• Includes earthworms and leeches.
• Clitellum: Specialized band for reproduction, aids in egg and sperm exchange.

Superphylum Ecdysozoa

• Includes phyla with protective cuticle exoskeleton, requires molting (ecdysis) for growth.

Phylum Nematoda

• Known as roundworms.
• Characteristics:
  • Mostly microscopic.
  • Pseudocoelomates.
  • Hydrostatic skeleton.
  • No circulatory system.
• Significance:
  • Includes model organism C. elegans for genetic research.

Phylum Arthropoda

• Largest phylum with over 1.1 million species.
• Characteristics:
  • Jointed appendages for various functions (legs, antennae, wings).
  • Segmented body into tagmata (e.g., head, thorax, abdomen).
  • Chitinized exoskeleton, requires molting.

Subphyla of Arthropoda

Subphylum Chelicerata

• Includes spiders, ticks, scorpions, horseshoe crabs.
• Features:
  • Chelicerae (fangs, mouthparts).
  • Book lungs for respiration in spiders.

Subphylum Myriapoda

• Includes centipedes and millipedes.
• Features:
  • Numerous repeating body segments.

Subphylum Crustacea

• Includes crabs, shrimp, lobsters, krill, pill bugs.
• Features:
  • Mostly aquatic, some terrestrial (e.g., pill bugs).
  • Two tagmata: cephalothorax and abdomen.
  • Exoskeleton often hardened with calcium carbonate.

This lecture covered the diverse body plans and systems in mollusks, the segmented structure of annelids, and the unique exoskeleton characteristics of ecdysozoans, particularly focusing on roundworms and arthropods.