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Lecture #11 Worms, Worms & Worms Phylum Platyhelminthes Phylum Nematoda Phylum Annelida Current Molecular Classification • Clade Lophotrochozoa: – Phylum Platyhelminthes - worms – Phylum Annelida - worms – Phylum Mollusca – clams, scallops, squids, snails etc… • Clade Ecdysozoa: – Phylum Nematoda - worms – Phylum Arthropoda – crustaceans, spiders & insects Phylum Platyhelminthes • • • • • flatworms – 20,000 species “platy” – flat “helminth” = worm unsegmented flatworms novel developments (vs. Sponges and Cnidarians): – development of bilateral symmetry and three embryonic (triploblastic) tissues in these worms – development of a head-like region = cephalization – development of an excretory system = protonephridia Phylum Platyhelminthes • flatworms are divided into two lineages – A. Non Parasitic – Class Turbelleria (free-living) – B. Parasitic: – Class Monogenea (ectoparasitic) – Class Trematoda (parasitic) = flukes – Class Cestoidea (parasitic) = tapeworms Features common to Phylum Platyhelminthes • 1. triploblastic – three germ layers: ectoderm, mesoderm and endoderm – mesoderm muscle • 2. bilateral • 3. flattened body plan – thin • 4. acoelomate • 5. protonephridia for an excretory system • 6. no circulatory or respiratory system – exchange by diffusion • 7. incomplete digestive system – mouth, no anus • 8. most are hermaphroditic (monoecious) Features common to all flatworms • protonephridia for osmoregulation (water balance) • for the flatworms – influx of water into their bodies from their environment • this excess water is removed through protonephridia • comprised of flame cells or flame bulbs that draw the water in and expel it back to the outside • free-living flatworms – e.g. Planaria & Dugesia • marine and freshwater • bottom dwellers • over 4,500 species to date • less than 1 cm long in most species • free-living species are shades of black, brown and gray • larger species can be brightly colored https://www.youtube.com/watch?v=wn3xluIR h1Y Class Turbellaria • incomplete digestive system – most turbellarians are carnivorous and feed on small invertebrates or scavenge dead animals – both extracellular and intracellular – food enters the pharynx – enzymes secreted into the pharnyx for extracellular digestion – food enters the intestine where cells phagocytose smaller food particles and complete digestion intracellularly Class Turbellaria • tubellarians have net-like nervous system (like most flatworms) • nerve trunks that run the length of the body – neurons organized as sensory and motor and association – seen in higher order animals like humans • accumulation of neurons near the head – function as a brain • also have two auricles – have neurons for detecting chemicals • two eyespots called ocelli at the head for detecting light • Asexual reproduction: reproduce asexually via transverse or longitudinal fission Class Turbellaria – regenerate the missing body regions once they separate head regeneration: https://www.youtube.com/watch?v=kndPpqC6 -78 • • • • Class Trematoda 8,000 species parasitic flatworms called flukes wide, flat shape to oval or elongate body plan: like the turbellarians in structure – large intestine that splits into two tubes – hermaphroditic – outside is covered with an organic layer of proteins + carbohydrates = glycocalyx • can help evade the host’s immune system • Flukes: – attachment through an oral sucker that surrounds the mouth – a second sucker – acetebulum – located ventrally in the middle of the body • e.g Clonorchis sinensis – liver flukes – infects 30 million people annually – mostly in Asia – adult flukes live in the human liver – definitive host – life cycle also requires an intermediate host – usually a mollusc e.g. Schistosoma – blood flukes e.g. Paragonimus – lung fluke e.g Clonorchis sinensis – liver flukes • Schistosoma – blood flukes • adult flukes live in the human bloodstream • dioecious – males are shorter and thicker • female is long and slender – carried in a ventral canal on the male • life cycle – 1. copulation is continuous – constantly mating pairs of worms (female, smaller & thinner) – 2. eggs are released in feces and releases miracidia into freshwater – 3. penetrates a snail to continue it life cycle – 4. larval form leave the snail and penetrate human flesh (creates a rash) – 5. once in humans the larvae form adults Class Cestoidea • • • • • • tapeworms 3,500 species endoparasites – vertebrate digestive system 1 mm to 25m in length nearly all monoecious lack a mouth and digestive tract – absorb nutrients by diffusion • • • consist of a long series of repeating units called proglottids (repeating reproductive segments) attachment by a scolex – holdfast that attaches the worm to its host live in a very stable environment – intestinal tract has few variations – proglottids are filled with reproductive structures (male and female) • devoted to making eggs • BUT the male organs mature before the female – no self fertilization • fertilized eggs accumulate in the uterus (black under the microscope) • the further back in the tapeworm – the more mature the proglottid and the more eggs • the oldest proglottids filled with eggs = gravid proglottid • gravid proglottid breaks off from the worm and breaks open to release the fertilized eggs • the lost proglottid is remade up near the neck • beef tapeworm – Taenia saginata – – – – – adults live in small intestine may reach lengths of 25 meters!! 80,000 eggs per proglottid eggs released in human feces egg develops and forms a 6 hooked larva called the onchosphere – intermediate host – cattle – onchospheres travel from the gut to the skeletal muscle where they encyst over long periods of time – when eaten by humans releases the worm into the human bloodstream – scolex attaches to the intestine wall of the human https://www.youtube.com/watch?v=EEBbtwG qPEs oncospheres Phylum Annelida • characteristics: – – – – 1. segmented – into metamers 2. bilaterally symmetrical 3. coelomate 4. closed circulatory system • • • • large vessels that function as hearts series of vessels closed off from the tissues circulatory fluid = blood gas exchange by capillary beds – 5. complete digestive system • mouth --> storage crop grinding gizzard absorptive intestine anus – 6. excretory system – pairs of nephridia in each segment – 7. well developed longitudinal and circular muscles • for locomotion = https://www.youtube.com/watch?v=0Texxu3p7I8 • excretion by nephridia – filters body fluid – minerals and water reclaimed and put back into the bloodstream – wastes expelled to the outside – very similar to the vertebrate nephron Phylum Arthropoda • characteristics: – 1. metamerism – segmentation PLUS specialization of body segments for specific functions – 2. chitinous exoskeleton for support and protection • growth achieved through molting • number one reason for arthropod success – 3. paired, jointed appendages – 4. open circulatory system & complete digestive tract – 5. metamorphosis often seen to achieve sexual maturity Phylum Arthropoda • 4 subphyla – 1. Subphylum Chelicerata • Class Merostomata – horseshoe crabs • Class Arachnida - spiders • Class Pycnogonida – sea spiders – 2. Subphylum Crustacea – 6 classes • Class Branchipoda – brine shrimp • Class Malacostraca – shrimp, lobsters, crab, crayfish • Class Maxillopoda – copepods and barnacles – 3. Subphylum Hexapoda • insects – 4. Subphylum Myriapoda • millipedes and centipedes Subphylum Chelicerata • includes the spiders, mites, ticks, horseshoe carbs and sea spiders • two specialized body segments – 1. cephalothorax – for sensory, feeding and locomotion • first pair of paired appendages = chelicerae (feeding) • second pair = pedipalps (feeding) • followed by paired walking legs – 2. abdomen • contains digestive, reproductive, excretory and respiratory organs chelicerae Subphylum Crustacea • crayfish, shrimp, lobsters and crabs • plus the copepods, fairy shrimp, isopods (pillbugs), amphipods and barnacles barnacle copepod isopod • crayfish: known as a Decapod – – – – Class Malacostraca at least ten pairs of jointed appendages body plan: cephalothorax and abdomen exoskeleton extends all the way around the body = carapace abdomen takes the form of the “tail” Decapod Appendages • 10 pairs of appendages used for feeding and walking • Head - sensory – 1. antennae – 2. antennules • Thorax – feeding and walking – 1 3. Maxillopeds (feeding) – 4 8. Periopods (walking legs) • Abdomen - swimming – 1 5. Pleopods (Swimmerets) – 6. Uropod (part of telson) Class Malacostraca • feeding and digestion: prey on other invertebrates, eat plant matter and scavenge dead and dying animals – 1st 8 pairs of appendages are for food detection and handling – enlargened stomach – part of which is specialized for grinding – digestive gland called a hepatopancreatic gland - secretes digestive enzymes into the stomach – intestine extends from the stomach – intestine ends in an anus – important role in water and salt regulation • circulation: similar in all arthropods – open system Class Malacostraca – tissues are bathed in body fluids containing oxygen binding pigments – do have a heart • respiratory: feathery gills attach to the bases of the walking appendages – water is moved over the gills for the exchange of gases between the oxygenated water and the body fluids gills Subphylum Hexapoda- Class Insecta • 2 classes: Entognatha and Insecta • insect body plan: – body is divided into: head, thorax and abdomen – head bears a single pair of antennae, mouthparts (maxillae, mandibles), compound eyes and ocelli – thorax bears three pairs of legs & wings (in some insects) locomotion: varied methods from crawling to flying Class Insecta • feeding and digestion: – head bears mouthparts for food handling and sensory • mandibles for chewing • maxillae for cutting – digestive tract - long, straight tube of foregut, midgut and hindgut The Insect Eye ocelli compound eye • ocelli + several compound eyes • ocelli = 500 – 1000 receptor cells beneath a single circular lens • compound eyes found in many adult insects – better suited for detecting movement rather than for forming an image • compound eyes consists of a few to 28,000 receptors called ommatidia – fuse into a multifaceted eye • ommatidia –light-gathering structure – covered with a cornea, contains a cone (lens) – base is a rhabdom – converts light energy into a nerve impulse • excretion: Malphigian tubules – open into the junction of the midgut and hindgut – ions, water and other critical materials are reabsorbed from the rectum back into the body fluid – nitrogenous wastes move into hindgut – main excretory product - uric acid • gas exchange : tracheae – tubes that open to the air via the spiracles along the body • spiracles lead to tracheal tubules that carry air to the muscles – gas exhange • inspiration through the thoracic spiracles and expiration through the abdominal spiracles Features common to Phylum Echinodermata • 1. triploblastic • 2. pentaradial symmetry in adults; bilateral symmetry in larvae • 3. coelomate • 4. internal endoskeleton made of calcerous (bony) plates called ossicles • 5. water vascular system for locomotion Phylum Echinodermata • approximately 7,000 species • all are marine • living echinoderms are classified into 6 classes – 1. Asteroidea – sea stars – 2. Ophiuroidea – brittle stars and basket stars – 3. Echinodea – sea urchins and sand dollars – 4. Holothuroidea – sea cucumbers – 5. Crinoidea – sea lilies and feather stars – 6. Cocnentricycloidea – sea daises Class Asteroidea • • • • • • sea stars about 1,500 species live on hard substrates in marine environments five arms radiating from a central disc central disc has a mouth on its ventral side (oral surface) opposite surface is the aboral surface with an anus Water vascular system • water-filled canals for locomotion • water enters into a ring canal through a stone canal and a sieve-like pore called the madreporite • five radial canals (or multiples) branch from the ring canal and run down each arm • extensions off of the radial canals are called tube feet madreporite -tube feet • extensions off the ring canals • project to the outside & have suction cups at its end • inside the body they end as a bulblike, muscular ampulla • when the ampulla contracts- forces water into the tube which then extends • contraction of tube feet back into body pulls sea star forward: locomotion https://www.youtube.com/wa tch?v=2DFXGafpGkQ