Presentation on theme: "P. Nemertea Ribbon Worms"— Presentation transcript:
1P. Nemertea Ribbon Worms Non-parasitic life cycleMostly marineDigestive tract is complete***Have a long proboscis which lays within the rhynchocoel, and closed circulatory system****.Most are less than 20 cm long however Lineus longissimus is reported to measure 60 m in length!
4Nemerteans are voracious predators with well-developed chemical senses scyphozoan medusafish eggs
5FRESHWATER NEMERTEA: THE PROBOSCIS WORMS, PROSTOMA SP FRESHWATER NEMERTEA: THE PROBOSCIS WORMS, PROSTOMA SP. COLLECTED FROM WISCONSIN.
6PROSTOMA SP. NOTE THE SENSORY GROOVE AND 3 PAIRS OF EYES
7P: MesozoaMembers of the phylum are minute, ciliated animals only mm in length.Highly specialized parasites or symbionts living in marine invertebrates.Most are composed of only cells arranged in two layers.
11P: MesozoaThe two layers are not homologous to germ layers of other metazoans.It is still unclear as to whether they are degenerate platyhelminthes (flatworms) or truly-primitive, basal metazonas.Mesozoa were once thought to be evolutionary intermediate forms between Protozoanas and Metazoans, but now they are thought to be degenerate or simplified metazoa.
12The Big PictureFlatworms are a divers group of bilaterally symmetrical invertebrates with a head region.A large proportion of these are parasitic and having complex life cycles.The diversity of life cycle strategies must overcome the small probability of finding and infecting a host were the parasite can grow and reproduce.