Nemertea

1. Nemertea By: Alex Wolf and Sheila Ghanian

2. Basic Information • Common Name: Ribbon Worm Niponnemertespuler Tubbulanusribon worm Giant ribbon worm

3. Body of Nemertea • Body Symmetry: Bilateral symmetry • Body Plan: Acoelomate • Support/Movement System: • Nemertea move slow • Most use external cilia to glide on surfaces • Smile produced to help glide • Larger species crawl by muscular waves • Aquatic species swim by undulations

4. Nutrition • Mode of nutrition: heterotrophic • Eating: eats bacteria ingested through pharynx at anterior end. • Digestion: flows through one way

5. Gas Exchange • occurs by cutaneous respiration, which involves simple diffusion through the skin • Nemertea do not need a formal respiratory system because of cutaneous respiration

6. Defense Mechanism • one mechanism is the eversible proboscis, which can be used to inject toxins or poisons into predators in the same way as for prey→ a blind-ended tube that often has nail-shaped structures attached to the end, lies dorsal to digestive tract, is contained within hydrostatic chamber called the rhynocoell, and can be everted and retracted via hydrostatic pressure or retractor muscles • a second mechanism is the secretion of large amounts of mucous

7. Excretion/ Water Balance • Nemerteans have a metabolic excretory system→ pairs of nephridial ducts • osmoregulation is under the control of the cerebral ganglion, and involves the circulatory system and photonephridia • the secretion of large amounts of mucous also can help decrease the inflow of freshwater (freshwater species) • with the exception of the above information, the excretory system and the osmoregulation mechanism have not been well-studied

8. Reproduction • most Nemerteans reproduce sexually (marine species), but some species reproduce asexually (usually freshwater and terrestrial species) • sexual reproduction: male and female organisms and gametes(sperm and egg)→ fertilization occurs outside the female’s body in the water→ after fertilization occurs, the egg either develops into a smaller version of the adult (what happens with humans), or grows into a larva that eventually becomes an adult via metamorphosis

9. Reproduction • there are two ways that Nemertea reproduce asexually • first way: body fragmentation→ smaller fragments of the parent organism form • second way: freshwater Nemertea are hermaphroditic→ self-fertilization→ male gonads form before female gonads, and then a sperm fertilizes an egg internally

10. Response to Stimuli • Nemertea have a well-developed nervous system with cephalic ganglia and nerve network connecting various sensory organs→ usually there are a pair of cerebral ganglia, a pair of ganglionated nerve cords, and a main nerve net • Many Nemertea possess eyes that are located towards the front of the animal’s body near the cephalic ganglia. Other sense organs include cephalic grooves and sensory pits that perform chemotactic functions.

11. More Characteristics • Nemertea are the first group of acoelomate animals to have a complete digestive system (mouth and anus) and a true circulatory system • eversible proboscis • Nemertea are the simplest animals to have a circulatory system with blood

12. The End