I.General Information: 1.Round, unsegmented bodies tapered at each end 2.Pseudocoelom- body cavity filled w/fluid that distributes oxygen & nutrients so don’t have circulatory system 3.Tube-within-a-tube body plan 4.2 body openings- mouth & anus 5.Size- microscopic to about 1 meter 6.Bilateral symmetry 7.Triploblastic 8.Most are free living some are parasitic
II. Body a.Cuticle- Thin, tough outer skin may have spines or scales for protection. Not easily digested by host Most molt about 4x during life b.Longitudinal muscle- Produces thrashing motion Creates S- or C-shaped curves
III. Digestion/Feeding a.Parasitic, free living, saprobes (decomposers) b.Mouth- buccal cavity May have hooks or suckers for attaching (parasite) Sensory organs (“lips”) may be present c. Pharynx- muscular organ that rhythmically pumps food thru digestive tract d.Intestine- long tubular organ where digestion/absorption occur e.Rectum/Anus- end of digestive tract where wastes are excreted.
IV. Nervous System a.Dorsal & Ventral Nerve Cord- run along upper & lower surface of body sending nerve impulses to anterior end. b.Nerve ring- simple brain picks up stimuli from nerve cords. c.amphids – anterior (towards the head) depressions used for sensing chemicals in the water d.phasmids – posterior (towards the tail) depressions used for sensing chemicals in the water
V. Respiration a.All roundworms breathe by diffusion of oxygen into moist skin and carbon dioxide out of moist skin.
VI. Excretory System a.Excretory ducts collect liquid waste b.Excretory pores excrete collected liquid waste thru skin
VII. Reproductive system a.Dioecious b.Males are usually smaller than females c.Most lay eggs that hatch into larva- oviparous d.Some give birth to live larva- viviparous e.Some create eggs which they retain & hatch inside body- ovoviviparous f.Some males may have bursa- flap of skin used to hold female while transfering sperm May also have copulatory spikes or spicules which are penis-like
g. Typical Nematode Life Cycle Egg L1- 1 st larval stage L2- 2 nd larval stage L3- 3 rd larval stage L4- 4 th larval stage Adult Molt in between each larval stage to get bigger Dauer- after 1 st molt larvae may enter this hibernation stage if overpopulation pheromone is present, temperature is too high, or no food present. Parasitic nematodes have different life cycles
VIII. Economic/Environmental Importance a.Free-living soil nematodes & saprobes- important as recyclers of necessary nutrients back to soil. 1 m 2 of mud = 4 million nematodes! b. Parasitic nematodes- Cause disease Plants Vertebrates Humans
DAILY QUIZ #1 1.Nematodes are a. Monoeciousb. Dioecious 2.Nematodes are the first animals we have study to have a.Nervous systemb. Mouth and anusc. Excretory system 3.The structure that helps prevent digestion of parasitic nematodes is the a. Cuticleb. Hookc. sucker 4.Which is true about nematodes a.Males are larger than females b.Females are larger than males c.Neither A or B because they are hermaphrodites 5.Which is not a characteristic of nematodes? a.Bilateral symmetryc. Pseudocoelom b.Triploblastic d. Segmented