Roundworms, Mollusks, and Annelids

Objectives

• Summarize traits of nematode invertebrates
• Summarize traits of mollusks
• Summarize the characteristics of annelids
• Give an overview of the phylum Arthropoda

Roundworms

• Make up phylum Nematoda
• 1 mm to 7 m long
• Have a pseudocoelom
• Have complete digestive system
• Have hydrostatic skeleton

Roundworm Reproduction

• Sexual
• Sperm and egg by separate individuals
• Internal fertilization
• As many as 100,000 eggs laid a day
• Eggs hatch into larvae

Roundworm Ecology

• Free-living or parasitic
• Free-living in fresh water
• Parasites: hookworm, pinworm

Mollusks

• 80% are gastropods
• Hard outer shell
• Mantle: layer of tissue between shell and body
• Mantle cavity pumps water for filter feeding
• Radula: feeding organ with teeth in front of mouth

Mollusks

• Have coelom
• Have complete digestive system
• Excretory system of nephridia
• Aquatic mollusks "breath" with gills
• One or two hearts; open or closed system

Mollusk Reproduction

• Sexual
• Gametes released into mantle cavity
• Fertilizaed eggs develop into larvae

Mollusk Classes

• Gastropods - use a foot to crawl
• Bivalves - often sessile filter feeders
• Cephalopods - carnivores in marine habitats

Annelids

Annelids

• 1 mm to 3 m long
• Have a coelom
• Have closed circulatory system like cephalopods
• Have excretory system with tubular nephridia
• Have complete digestive system

Annelids

• Have brain and sensory organs
• Gills for gas exchange
• Segmentation for more efficient movement
• Regeneration of rows that break off

Annelid Reproduction

• Asexual or sexual
• (Leeches only reproduce sexually)
• Asexual reproduction by budding or fission

Annelid Ecology

• Deposit feeders, e.g, earthworms
• Polychaetes on ocean floor
• Leeches

Arthropod Intro

Arthropoda

• Largest of all phyla
• 1 mm to 4 m long
• Segmented body with hard exoskeleton
• Jointed appendages

Body Segments

• Head
• Thorax
• Abdomen