1. Free-Living Roundworms
Phylum Nematoda
Free-Living Roundworms

2. Characteristics Round, unsegmented bodies tapered at each end.
Pseudocoelem- body cavity filled with fluid that distributes O2 & nutrients. No circulatory system.

3. Characteristics Tube within a tube body plan
2 body openings= mouth & anus
Bilateral symmetry
Size: microscopic to about 1 meter.
Triploblastic
Most are free living some are parasitic.

4. Class Secernentea (Phasmidea)
Phasmids on tail end.
Phasmids- paired glandular or sensory structures
Poorly developed amphids on anterior end.
Amphids similar to phasmids.
Contains excretory system
Both free-living and parasitic species
About 5,000 species

5. Class Adenophora (Aphasmidia)
Phasmids absent
Most are free-living
Some parasitic species occur
About 3,000 species

6. Body Plan Cuticle Longitudinal Muscle
Thin, tough outer skin may have spines or scales for protection.
Not easily digested by host
Most molt about four times during life
Produces thrashing motion
Creates S- or C-shaped curves

7. Digestion/ Feeding Parasitic, free living, saprobes (decomposers)
Mouth- buccal cavity
May have hooks or suckers for attaching (parasite)
Sensory organs (“lips”) may be present
Pharynx- muscular organ that rhythmically pumps food thru digestive tract
Intestine- long tubular organ where digestion/absorption occur
Rectum/Anus- end of digestive tract where wastes are excreted.

8. Nervous System
Dorsal & Ventral Nerve Cord- run along upper & lower surface of body sending nerve impulses to anterior end.
Nerve ring- simple brain picks up stimuli from nerve cords.

9. Nervous System
amphids – anterior (towards the head) depressions used for sensing chemicals in the water
phasmids – posterior (towards the tail) depressions used for sensing chemicals in the water

10. Respiration
All roundworms breathe by diffusion of oxygen into moist skin and carbon dioxide out of moist skin.

11. Excretory System Excretory ducts collect liquid waste
Excretory pores excrete collected liquid waste through skin

12. Reproductive System Dioecious: Males are usually smaller than females
Oviparous: lay eggs that hatch into larva
Viviparous: Some give birth to live larva
Ovoviviparous: Some create eggs which they retain & hatch inside body

13. Reproductive System
Some males may have bursa- flap of skin used to hold female while transferring sperm
May also have copulatory spikes or spicules which are penis-like

14. Typical Nematode Life Cycle
Stages
Molting
Egg
L1- 1st larval stage
L2- 2nd larval stage
L3- 3rd larval stage
L4- 4th larval stage
Adult
Molt in between each larval stage to get bigger
Dauer- after 1st molt larvae may enter this hibernation stage if overpopulation pheromone is present, temperature is too high, or no food present.

15. Economic/ Environmental Importance
Free-living soil nematodes & saprobes- important as recyclers of necessary nutrients back to soil.
1m2 of mud = 4 million nematodes!
Parasitic nematodes- Cause disease in…
Plants
Vertebrates
Humans

16. Reproductive System
Female
Male

17. Exit Ticket
NO TALKING
NO NOTES

18. Nematodes are
Monoecious
Dioecious

19. Nematodes are the first animal we have studied to have…
Nervous System
Mouth and Anus
Excretory System

20. The structure that helps prevent digestion is the…
Cuticle
Hook
Sucker

21. Which is true about nematodes?
Males are larger than females
Females are larger than males
Neither A or B because they are hermaphrodites

22. Which is not a characteristic of nematodes?
Bilateral symmetry
Triploblastic
Pseudocoelem
Segmented