MARB 435 Lecture 10 Outline of Last Lecture 1 Ctenophore Morphological Terms 2 Ctenophore Symmetry 3 Fossilized Ctenophores 4 Invasive Ctenophores 5 Mnemiopsis Ctenophores blossoms 6 Introduction of Bilateria 7 Types of Symmetry 8 Unusual types of Symmetry 9 Bilateria Adaptive Significance of Bilateral Symmtery 10 Cephalization 11 Germ Layer Table 12 Body Cavities 13 Coelom Functions 14 Genreal Excretion 15 Nitrogenous Waste Products 16 Urine 17 Steps of Excretion 18 Excretory Organs in Bilateria In 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 Lecture 1 Phylum Platyhelminthes 2 Fossil Record 3 Internal Morphology Vocabulary 4 Turbellaria Body Wall 5 Feeding Habitats Strategies 6 Toxic Flatworms 7 Asexual Reproduction Regeneration 8 Sexual Reproduction 9 Parasitism 10 Challenges of and Endoparasitic Lifestyle 11 Tapeworm Lifecycle 12 Class Trematoda Digenea 13 Schistosomiasis 14 Snails and Digeneans Current Lecture Phylum Platyhelminthes These organisms are soft bodied and have no cuticle or skeleton this mean no circulatory system 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 Record When 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 Tubellarians The 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 Vocabulary To 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 cavity Turbellarian Body Wall The turbellaria have a multiciliated epidermis and each cell bears multiple cilia They rely particularly 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 Strategies Platyheminthes 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 and eat 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 mouth Toxic Flatworm Toxic 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 Regeneration Regeneration 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 1 300 th 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 Reproduction As 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 that receives the sperm Turbellarians develop directly and some produce ciliated planktotorophic larvae The larvae is either Muller s or Gotte s larva Parasitism Parasitism is he symbiotic interaction in which one