Nematoda

roundworms

Characteristics

Free-living or parasitic Most very small < 2mm, some 1m long Abundant (100 in a cupful of soil) >20,000

named species, many others undescribed Radial symmetry - cylindrical body Pseudocoelomate - false body cavity Tough cuticle must be shed to grow Has cephalization

Organization

Specialized cellsOrganized Tissues

Tripoblastic - 3 cell layersOrgan systems

Muscles - only longitudinal Reproductive Digestive - Complete gut w/ mouth and

anus

Reproduction

Usually diecious - sexes distinctparenthogenesis common - asexual

form of reproduction where embryo grows and develops without fertilization by a male.

Nematode adult anatomy

Nematode Locomotion

Pressurized pseudocoelom holds shape

Longitudinal muscles that pull against that pressure to provide a spiral

lashing motion

For burrowing and penetrating host tissues

Feeding Modes of Nematodes

Microbivores - select bacteria and fungi from soil and water

Predators eat small prey, or pierce and suck out larger prey

Plant parasitesAnimal parasites

Nematode Diets and Mouths

Classification

1. Ascaris - Intestinal Roundworm genus Ascaris, females up to 30 cm 67% used to be infected in S.E. United

States adults eat intestinal chyme heavy infections cause abdominal pain

and allergic reactions 1. or death, in heavy infections of children

Ascaris Internal Migration

eggs transferred from feces to food or mouth by hand; hatch in intestine

larvae penetrate bloodstream, go to lungs

break out into alveoli and crawl up trachea to esophagus, swallowed again

adults live free in small intestine

Ascaris Life Cycle

Dog Heartworm Life Cycle

Adult lives in dog’s heart muscle releases eggs into bloodstream, which hatch into small larvae (“microfilariae”)

larvae enter a mosquito that bites the dog

enter another dog by mosquito’s next bite

migrate to heart and grow inside muscleDog Heartworm

Dog Heartworm

Other Parasitic Nematodes

•hookworm, pinworm, trichinosis, river blindness, etc. •cuticle protects against immune system and enzymes •can do without oxygen

Hookworm: Necator Americanus

Dog Hookworm Lifecycle

Trichinella: Trichina worm

Pinworm: Enterobius

Wucharia: Filial worms