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Phylum Platyhelminthes

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Presentation on theme: "Phylum Platyhelminthes"— Presentation transcript:

1 Phylum Platyhelminthes
Lecture #11 Worms, Worms & Worms Phylum Platyhelminthes Phylum Nematoda Phylum Annelida

2 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

3 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

4 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

5 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)

6 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

7 Class Turbellaria 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

8 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

9 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

10 Class Turbellaria Asexual reproduction: reproduce asexually via transverse or longitudinal fission regenerate the missing body regions once they separate head regeneration:

11 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

12 Flukes: e.g Clonorchis sinensis – liver 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

13 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

14 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

15 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

16 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 oncospheres

17 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 =

18 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

19 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

20 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

21 Subphylum Chelicerata
chelicerae 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

22 Subphylum Crustacea crayfish, shrimp, lobsters and crabs
plus the copepods, fairy shrimp, isopods (pillbugs), amphipods and barnacles barnacle copepod isopod

23 Class Malacostraca crayfish: known as a Decapod
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”

24 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)

25 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

26 circulation: similar in all arthropods – open system
Class Malacostraca circulation: similar in all arthropods – open system 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

27 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

28 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

29 The Insect 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

30 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

31 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

32 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

33 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

34 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

35 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

36 extensions off the ring canals
-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

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