Nematodes The Roundworms

Characteristics Round cross section First group of organisms to have 2 openings to digestive tract Unsegmented, smooth outer covering (cuticle) that needs to be molted Wiggle from side to side (since they have only longitudinal muscles) Tapered at both ends of organisms

Examples of Nematodes Just Kidding! Make up 15% of the biomass at the bottom on freshwater lakes The majority of round worms are not parasites

Examples Hookworms- eggs are passed through human waste products, hatch into to larvae in soil, burrow in feet Common in warm climates where there is not good sanitation

Trichinella- parasites found in pigs Trichinella- parasites found in pigs. Eggs are transmitted in meat- cooking pork kills eggs Trichonosis- eggs hatch, larva are carried to muscles where they burrow, painful

Digestive System Most nematodes are free living and have a digestive track. Some are parasitic and absorb food from their host.  Mouth Pharynx- Muscular tube that acts as a pump to bring food from the mouth Intestine – A long tube in which food is both digested and absorbed. Anus- Place where undigested food leaves

Respiratory and Circulatory system Nematodes rely on diffusion to obtain oxygen from their environment and to have materials travel through their body. Nematodes must have a wet film on their body in order to have diffusion in/out of body.

Reproduction Most species have both male and female organisms. Fertilization is internal and fertilized eggs are then released from the female. The eggs hatch into larva with will eventually develop into a worm. A few species can reproduce asexually by parthenogenesis Embryos form from cells in the adult

Nematode Facts A handful of soil will contain 1000’s of microscopic, free living nematodes. Nematodes help enrich soil Nematodes can stop all their life activities and go to sleep when conditions are unfavourable. One species of Nematode is a parasite of the Sperm Whale and grows up to 13 meters long.