MARB 435 Lecture 10 Outline of Last Lecture1. Ctenophore Morphological Terms2. Ctenophore Symmetry3. Fossilized Ctenophores4. Invasive Ctenophores5. Mnemiopsis (Ctenophores) blossoms6. Introduction of Bilateria7. Types of Symmetry8. Unusual types of Symmetry9. Bilateria: Adaptive Significance of Bilateral Symmtery10. Cephalization11. Germ Layer Table12. Body Cavities13. Coelom Functions14. Genreal Excretion15. Nitrogenous Waste Products16. Urine17. Steps of Excretion18. Excretory Organs in BilateriaIn today’s lecture, the notes introduce the Phylum Platyhelminthes commonly known as flatworms. The notes discuss various classes of flatworms, morphology, and reproduction.Outline of Current Lecture1. Phylum Platyhelminthes2. Fossil Record3. Internal Morphology Vocabulary4. Turbellaria Body Wall5. Feeding Habitats & Strategies6. Toxic Flatworms7. Asexual Reproduction: Regeneration8. Sexual Reproduction9. Parasitism10. Challenges of and Endoparasitic Lifestyle11. Tapeworm Lifecycle12. Class Trematoda/Digenea13. Schistosomiasis14. Snails and DigeneansCurrent LecturePhylum PlatyhelminthesThese organisms are soft bodied and have no cuticle or skeleton this mean no circulatorysystem. They are acoelomates and tripoblastic and bilaterally symmetrical. Similar to barnacles these species are hermaphrodites which is discussed in reproduction. They have no anus meaning they have a gastrovascular cavity; having a gastrovascular cavity means the species only has one opening. They have an organelle called neoblasts which are stem cells that develop into other cell types.Fossil RecordWhen looking at Platyhelminthes fossil records they are almost non-existent because of their soft body which shows poorly in fossils. The earliest fossil was found 40 million years ago in Baltic Amber and this fossil shows that some turbellarians (flatworms) were terrestrial organisms.Class TubellariansThe class tubellarians are commonly known as flatworms. They are very small organisms with a size ranging from 1 millimeter to 60 centimeters. They are marine and freshwater species. They like to inhabit environments that are classified as being humid and terrestrial. They are mostly benthic with a few pelagic forms.Internal Morphology VocabularyTo understand tubellarians the organisms must understand four very useful terms which are as followed.- Paranchyma- The mesodermal tissue between the gut and the epidermis- Gastrovascular Cavity- Species with having only one opening- Tricladida- Three branches of the gastrovascular cavity- Polycladida- The many branches of the gastrovascular cavityTurbellarian Body WallThe turbellaria have a multiciliated epidermis and each cell bears multiple cilia. They relyparticularly on cilia to glide over surfaces. They havea well developed and complex body wall musculature which is looping of circular, diagonal, and longitudinal musculature. These three types of musculature lay under the epidermis and basal lamina.Feeding Habitats & StrategiesPlatyheminthes follow a complex diet. They are commonly predators, detritivores, and herbivores. The detritivores feed on dead animals that sink to the bottom of the ocean or body of water. Herbivores feed on algae and diatoms. Diatoms are single-celled algae and many of them are planktonic. They feed by numerous ways the most common four are listed below.- Wrapping their body around their prey and covering it with a toxic mucus- Pinning down their prey to a substrate with adhesive organs to get a good grip to kill andeat- Many species have protrusable pharynx’s or proboscis (proboscis is a nose that’s long and mible like an elephant trunk)- Stabbing the prey with their penis which has stylets and projects from the mouthToxic FlatwormToxic flatworms can feed on mollusk species and other flatworms. The feeding time is determined by the size of the prey and the toxic flatworm can eat prey many times greater than its body mass. Toxic flatworms contain high levels of a toxin called TTX in its pharnx. TTX is tetradotoxin and it has no known antidote. It makes the prey that is exposed to TTX to undergo paralysis. The concentration of TTX is low immediately after feeding and slowly builds up again in toxic flatworms. TTX is currently being studied by it’s studied to be produced by the animal itself or it’s either by a bacterial symbionts. The only two ecological roles that are seen is that it’s a powerful defensive mechanism and assists in capturing prey for nutrients. Once again the TTX is a very powerful toxin and may studies have only been conducted on mice so it’s effects to humans aren’t well known.Asexual Reproduction: RegenerationRegeneration is a way that planarians reproduce. Regeneration is the process where organisms can regrow or develop from lost or destroyed parts or organs. If the heal or tail are bisected longitudinally each half grows a complete new head. Even 1/300th of an animal can grow into a complete new worm. Totipotent neoblasts (stem cells) ar responsible for regeneration of new tissue. Scientists have recently identified the gene responsible for regeneration the same gene might have similar functions in other animals. They can also reproduce asexually through fission. This is where an organism breaks off into numerous pieces which then develop into individual organisms.Sexual ReproductionAs stated earlier the planarians are hermaphrodites, so sexual reproduction is a complex process. When two planarians arrive to have sex they must first decide who shall play which role and this is a painful process. The planarians don’t like to be the mother because they have to start eating more and gathering more nutrients and food to ensure a positive birth of their offspring. So, the planarians reproduce through hypodermin insermination use their peniss and stab each other until one is impregnated; which shows immediately. The fighting is called ‘penis fencing’ which increases benefits of sperm donation over costs of sperm recipients. They have the same reproductive organs such as humans. Being hermaphrodites they have both reproductive organs such as paired testes, vas deferens, seminal vesicle, penis, ovaries and oviduct. Two additional reproductive organs are the vitellaria and the copulatory bursa. The vitellaria is an organelle that secrets a yolk around the egg and the copulatory bursa is a sac thatreceives the sperm. Turbellarians develop directly and some produce ciliated, planktotorophic