Nematodes

• Common name for phylum Nematoda is roundworms.
• Pseudocoelom - no true coelom
• Have peritoneal cavity (gut) but is not lined with mesoderm
• nematos - thread
• Characteristics of Nematodes

  • slender, unsegmented worms
  • free-living
  • parasitic
• Almost all species of vertebrates and many invertebrates serve as hosts for one or more types of parasitic nematodes.
• Nematodes have a digestive tract with two openings.
• The body plan is called a tube-within-a-tube
• The outer tube is the body wall and the inner tube is the digestive tract
• Food moves in one direction through the digestive tract
• The body systems of free-living roundworms tend to be more complex than those of parasitic forms
• Free-living is more complex to adapt to the environment and food sourcing
• Form of Nematodes

  • cylindrical shape
  • flexible non-living cuticle
  • lack of motile cilia or flagella
  • muscles only run longitudinally
• Outer body covering is a thick, noncellular cuticle secreted by the underlying epidermis, or hypodermis
• Most free-living roundworms are predators
• carnivores that use grasping mouthparts and spines to catch and eat other small animals.
• Roundworms exchange gases (respire) and excrete metabolic wastes like urea and ammonia through their body walls. (diffusion)
• They have no internal transport system
• Nematodes have simple nervous systems, consisting of several ganglia
• Ganglia - cluster of neurons acting as a brain
• A ring of nerve tissue and ganglia are found at the anterior end of their bodies
• Amphids - more complex sense organs that open around their heads
• Phasmids - open around the posterior end of the body
• amphids & phasmids are for chemorepulsion
• Together with the fluid in the pseudocoelom, create a hydrostatic skeleton
• Hydrostatic skeleton - is the use of coelom fluid to maintain the shape of the animal and allows for movement.
• Roundworms reproduce sexually
• They reproduce using internal fertilization
• Female: has ovary, passes them to the uterus, where they are fertilized.
• Male: Sperm cells made in the testis and stored in the vas deferens