Free-Living Roundworms Phylum Nematoda Free-Living Roundworms

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

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.

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

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

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

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.

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.

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

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

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

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

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

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.

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

Reproductive System Female Male

Exit Ticket NO TALKING NO NOTES

Nematodes are Monoecious Dioecious

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

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

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

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