INVERTEBRATESPhylum Ctenophora (Comb jellies)MRS. ADORA G. ILAC,RN,MSBIO

Phylum Ctenophora: Comb jellies possess rows of ciliary plates and adhesive colloblastsSuperficially they resemble cnidarian medusas however, the relationship between them is uncertainAbout 100 species, all are marineDiameter: 1-10cmMost are spherical or ovoid, some elongate and ribbonlike forms up to 1 m longCtenophora means "comb bearer": named for their eight rows of comblike plates composed of fused cilia

Phylum Ctenophora: Comb jellies possess rows of ciliary plates and adhesive colloblastsThe largest animals to use cilia for locomotion An aboral sensory organ functions in the orientation, and nerves running from the sensory organ to the combs of cilia coordinate movement

Phylum Ctenophora: Comb jellies possess rows of ciliary plates and adhesive colloblastsMost have a pair of long retractable tentacles, it bear adhesive structures called colloblast (lasso cells)When prey (mostly small plankton) contact a tentacle, colloblasts burst open. A sticky thread released by each colloblast captures the food, which is then wiped off the tentacle into the mouth

PROTOSTOMIA: LOPHOTROCHOZOAChoanoflagellateEumetazoaBilateriaProtostomiaLophotrochozoaPLATYHELMINTHESMOLLUSCAANNELIDA

Phylum Platehylminthes: Flatworms are acoelomates with gastrovascular cavitiesThere are about 20,000 species living in marine, freshwater, and damp terrestrial habitatsSome are free-living forms many are parasitic species (flukes, tapeworms)Are named because their bodies are thin between the dorsal and ventral surfaces (flattened dorsoventrally; platyhelminth means "flatworm")

Phylum Platehylminthes: Flatworms are acoelomates with gastrovascular cavitiesThey range in size: microscopic free living species to 20 m long (tapeworm)In contrast to the radiate animals (cnidarians and ctenophores), flatworms and all other bilateratians are tripoblasticHowever, flatworm just like radiate animals, have a gastrovascular cavity with only one opening. (Tapeworms lack digestive tract altogether and absorbs nutrients across their body surface)

Phylum Platehylminthes: Flatworms are acoelomates with gastrovascular cavitiesAre simpler than other bilateratians in lacking a body cavityAre acoelomates

4 CLASSESTurbellaria (mostly free-living flatworms)Monogenea (monogeneans)Trematoda (trematodes, or flukes)Cestoidea (tapeworms)

Classes of Phylum Platyhelminthes

Class and ExamplesMain CharacteristicsTurbellaria (mostly free-living flatworms; e.g., DugesiaMostly marine, some freshwater, a few terrestrial, predators and scavengers; body surface ciliatedMonogenea (monogeneans)Marine and freshwater parasites; most infect external surfaces of fishes; life history simple; a ciliated larva starts an infection on a hostTrematoda (trematodes, also called flukes)Parasites, almost always of vertebrates; two suckers attach to host; most life histories include intermaediate hostsCestoidea (tapeworms)Parasites of vertebrates; scolex attaches to host; proglottids produce eggs and break off after fertilization; no head or digestive system; life history with one or more intermediate hosts

Class TurbellariaNearly all free-living (nonparasitic)Mostly marineMembers of the genus Dugesia, commonly known as Planarians

PlanariansCarnivores: smaller animals or dead animalshave a simple nervous system consisting of a brain, sense organs, and branching nervesAs in cnidarians, the mouth of a flatworm is the only opening for its gastrovascular cavityDigestive tract (gastrovascular cavity)Nerve cordsMouthEyespotsNervous tissue clustersBilateral symmetry

Ganglia. Located at the anterior end of the worm, near the main sources of sensory input, is a pair of ganglia, dense cluster of nerve cellsVentral nerve cords. From the ganglia, a pair of ventral nerve cords runs the length of the bodyEyespotsGastrovascularcavityUndigested wastes are egested through the mouthDigestion is completed within the cells lining the gastrovascular cavity, which has three branches, each with has three branches, each with fine sub-branches that provide an extensive surface areaPharynx. The mouth is at the tip of a muscular pharynx that extends from the middle of the ventral side of the animal. Digestive juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastriovascular cavity where digestion continuesAn anatomy of planarian

Generalized Anatomy of a Planarian

Generalized Anatomy of a Planarian

Generalized Anatomy of a Planarian

Generalized Anatomy of a Planarian

Generalized Anatomy of a Planarian

PlanariansLack organs specialized for gas exchange and circulationThe flat shape of the body places all cells close to the surrounding water, and fine branching of the gastrovascular cavity distributes food throughout the animalNitrogenous waste in the form of ammonia diffuses directly from the cells into the surrounding water

PlanariansHave simple excretory apparatus that functions mainly to maintain osmotic balance between animal and its surroundings. This system consists of ciliated cells called flame cells that waft fluid through branched ducts opening to the outside

PlanariansThe evolution of osmoregulatory structures was a major factor in allowing some turbellarians to invade freshwater and even moist terrestrial environments

PlanariansMove by using cilia on the ventral epidermis, gliding along a film of mucus they secreteSome uses their muscles to swim through water with an undulating motionHas a head (cephalized) with a pair of eyespots that detect light and lateral flaps that function mainly for smellThe nervous system is more complex and centralized than the nerve nets of cnidarians

PlanariansCan modify their responses to stimuliCan reproduce asexually through regeneration. The parent constricts in the middle, and each half regenerates the missing endSexual reproduction also occursAlthough are hermaphrodites, copulating mates cross-fertilize

Class Monogenea and TrematodaLive as parasites in or other animalsMany have suckers for attaching to internal organs or to outer surfaces of the hostA tough covering helps protect the parasitesReproductive organs nearly fill the interior of these worms

Trematodes (Flukes)Parasitize a wide range of hostsMost species have complex life cycles with alternation of sexual and asexual stagesMany require an intermediate host in which larvae develop before infecting the final host (usually a vertebrate), where the adult worm lives e.g. Trematodes that parasitize human spend parts of their life histories in snail

Flukes and tapeworms are parasitic flatworms with complex life cyclesMature flukes in blood vessels of intestineHuman hostMaleFemaleSnail host1Sexual reproduction of flukes in human; fertilized eggs pass out in feces2Eggs hatch in water3Larva that infects snail4Asexual reproduction of flukes in snail5Larva that infects human6Larva penetrates skin and blood vesselsThe 200 millions people around the world who are infected with blood flukes (Schistotoma) suffer from body pains, anemia, and dysentery

MonogeneansAre external parasites of fishesLife cycle: simple, with a ciliated, free swimming larva starting an infection on a hostStructural and chemical evidence suggests that they are more closely related to tapeworm than trematodes

Class Cestoidea (Tapeworm)ParasiticAdults live mostly in vertebrates, including humansLack digestive tract, it absorbs food predigested by the host

ScolexHeadArmed with suckers and often menacing hooks that lock the worm to the intestinal lining of the hostUnits with reproductive structuresHooksSuckerHead

ProglottidsPosterior to the scolexA long ribbon of units which are little more than sacs of sex organsProglottids with reproductive structures

ProglottidsLoaded with thousands of eggs, are released from the posterior end of a mature tapeworm and leave the host's body with fecesIn one type of life cycle, human feces contaminate the food or water of intermediate hosts (pigs,cattle) and the tapeworm eggs develop into larvae that encysts in the muscles of these animals

ProglottidsHumans acquire the larvae by eating undercooked meat contaminated with cysts, and the worms develop into mature adults within the humanLarge tapeworms (20 m or more in length) can cause intestinal blockage and can rob enough nutrients from the human host to cause nutritional deficienciesNiclosamide: orally administered drug can kills the adult worms