sign in sign up
<<
Home , Cephalization, Dracunculus medinensis, Extracellular digestion, Flatworm, Head, Larva

Acoelomate à organs are embedded in tissue, not in any body space (like us) several phyla including Platyhelminthes share the following characteristics: like and

1. have 3 true embryonic tissue layers à only 1 “internal space” =digestive cavity (=triploblastic): 4. in terms of development these organisms are

between epidermis and digestive cavity is filled à develops first in during with a 3rd tissue layer = mesoderm gastrulation

à mesoderm allows development of muscle 5. most have bilateral layers in body wall such design allows for a “front end” à mesoderm allows more elaborate organs = more specialization and greater division of labor than in Cnidaria contains organs, simple

2. have true organs was a major new design

each is a combination of several tissues à more efficient search for food, mates, etc specialized for a particular function most animals before this were sedentary filter feeders

have various specialized cells but no true tissues or organs

and have 2 true tissue layers and a few simple organs

3. acoelomate=without body cavity

Animals - Phyla: Platyhelminthes; Ziser Lecture Notes, 2015.10 1 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 2

Phylum Platyhelminthes diverse array of parasitic species that parasitize () members of virtually every other animal phylum

[helminth = ] more specialization and division of labor among greater variety of tissues and organs simplest phylum at “organ level” of complexity acoelomate = no body cavity around digestive very diverse group but most are poorly known system

includes flatworms, flukes, tapeworms have three true tissue layers (primary germ layers) = triploblastic 25,000 living species, few fossils à no hard parts embryonic adult tissues tissues poorly known in fossil record but possible trails have ectoderm à epidermis been found from 565MY mesoderm à endoderm à gastrodermis may be first animal to have a head & tail may be first animal to have bilateral symmetry mesoderm makes more elaborate organs possible may be first animal to show directed movement à it differentiates into different kinds of wide variety of body forms all with bilateral symmetry muscle layers

body is usually elongated & slender, leaf-like or organ systems are better developed long & ribbon-like only major phylum that is mostly parasitic species à flattened body allows them to still rely on for exchange of gasses, of 4 classes, 3 are made up of entirely parasitic and wastes species

Body Wall range in size from few mm à 10 M long

A. Epidermis free living in ocean and freshwater habitats, moist soil

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 3 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 4 free living forms have single layer of ciliated cells eversible in some à can be extended to find food parasitic forms have syncytial layer that lacks cilia secretes to partially digest food before “eating” then suck in liquified food B. Muscle Layers once ingested enzymes are secreted into GVC two layers around body wall: circular muscle mostly extracellular some intracellular after phagocytosis longitudinal muscle Respiration no rigid for muscles to act on no thick muscle layers in (=feeding tube) make it “prehensile” flatworms have high surface/volume ratio

in some primitive species these muscle cells through flattened body wall resemble the epitheliomuscular cells of cnidarians

Feeding & Digestion free living forms are mainly carnivores beginnings of cephalization

most species are endoparasites ie. at least some members have distinct head incomplete digestive tract in most flatworms were probably the first creatures to have a “brain” in some digestive tract is highly branched to distribute food throughout the animal head with cephalic ganglia (~ simple brain)

some parasites (eg. tapeworms) completely lack a digestive system have pair of ventral nerve cords pharynx = muscular “throatlike” tube connected by ladder like interconnections Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 5 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 6

with true synapses between nerve cells some times produces a chain of zooids

Excretion à superficial resemblance to they are the simplest major phylum with an regeneration some wastes like ammonia are eliminated by diffusion flatworms have considerable powers of through the body wall regeneration others have primitive excretory system replacement of lost parts = protonephridia (tube closed at one end and exiting body at other end) also to recover from long food shortage

à in most takes the form of “flame cells” budding

cupshaped area with tuft of flagella beat of flagella tapeworms bud off proglottids (reproductive resemble candle flame under microscope sacs)

wastes and excess water diffuse into bulb polyembryony flagella create current to send wastes through tube which opens to outside of the body flukes

Reproduction one can produce 100’s of larvae

many reproduce both sexually and asexually increases chances finding a

Asexual Sexual

fission almost all flatworms are monoecious

() pinch in half

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 7 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 8 cross fertilization not self fertilization Classification

some with Class (planarians) free living ventral mouth locomotion by creeping on cilia and mucous

Class ectoparasites on skin or of simple cycle – no intermediate host

Class (flukes) all are parasitic endoparasitic flukes parasites in or digestive system up to 5 developmental stages in 2 or more hosts

Class (tapeworms) all are parasitic endoparasites in intestine bud long chains of proglottids

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 9 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 10

Class Turbellaria Feeding & Digestion (Planarians)

incomplete digestive tract in most almost all are free living àmouth, no

mostly bottom dwelling aquatic forms some have more than one mouth & more than one

mostly freshwater pharynx some are marine a few are even terrestrial (6 sp in US) mainly carnivorous

flattened, slender, ribbonlike or leaflike bodies feed on small crustacea, , ,

à still rely on diffusion for much exchange of

gasses, nutrients and wastes can detect food at a distance by chemoreceptors

often brightly colored entangle their prey in mucous

some marine forms have warning coloration wraps its body around prey

Body Covering some marine flatworms prey on molluscs using a

neurotoxin produced by symbiotic epidermis is ciliated

they engulf the whole animal or cover the opening of its secretes mucous trail and uses cilia to glide on it shell then produce the toxin to kill it

land planarians can glide ~6’/hr pharynx = muscular “throatlike” tube contains rhabdites extend prehensile proboscis to get prey

discharge into water swell and form protective mucous sheet around body secretes enzymes to help “predigest” prey may also release toxins to subdue prey and escape predators sucks up bits of prey Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 11 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 12 in intestine secrete enzymes which further digest prey auricles also contain chemoreceptors phagocytic cells in gastrodermis take up bits of pieces some turbellaria have for reacting to of prey and complete digestion intracellularly gravity

GVC extends to most parts of body Excretory System à also serves as distribution system protonephridia with “flame cells” undigested food is egested through mouth in freshwater forms this is mainly a way to get rid of Nervous System & excess water distinct head with cephalic ganglia metabolic wastes still excreted through body wall

pair of ventral nerve cords connected by ladder- reduced or absent in marine forms like interconnections Reproduction sense organs concentrated on head (vision, smell, touch, ) paired sense organs allow brain to discern the a. Regeneration direction of the stimulus turbellarians have considerable powers of 2 eyespots (=ocelli) regeneration

can’t form images, only detect light àreplacement of lost parts

auricles contain tactile cells àalso to recover from long food shortage

tactile cells are also distributed over body some can survive for months by self surface digesting up to 90% of their body Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 13 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 14

cross fertilization not self fertilization early researchers also reported learning by some with internal fertilization taught to run a maze cut in half and allowed to regenerate both new learned the maze quicker some with vaginas & penises - usually open through common genital pore à has never been repeated???

b. transverse fission in some monoecious flatworms mating ritual resembles a fight: the male organ consists of two dagger-like penises. during mating, two flatworms “penis fence” pinch in half: anterior end splits from each trying to get penis in genital pore of the other posterior end some without vagina or genital pore use hypodermic impregnation: sometimes produces a chain of zooids each tries to stab the other with its penis while trying to avoid getting stabbed by the other à superficial resemblance to segmentation the one who gets stabbed absorbs the sperm and fertilizes its

c. fragmentation fertilized egg is enclosed in cocoon which is attached by stalks to underside of stones or when alarmed, some land planarians can break up into dozens of “blobs of slime” most have no larval stage in a few hours each piece will become a new worm emerge as juveniles that grow into adults Sexual Reproduction a few marine species produce -like most are monoecious (hermaphrodites) (=Mullers larva)

during breeding season each individual develops àciliated ball of cells (has 8 ciliated lobes)

both male and female organs

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 15 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 16 Examples of Turbellarians eg. some marine planarians have symbiotic zoochlorella (algae) or feed on algae eg. common in fw streams some marine forms also have “kleptonematocysts” eg. they eat cnidarian polyps and keep the up to 20 pharynxes each with a mouth stinging cells to use for defense

eg Terricola = land planarians

fraction of an inch to almost 1’ long

creatures of dark or dim light

no , 2 eyes or 100’s of eyes

hunters and scavengers

some terrestrial planarians are fast enough to catch fruit (Drosophila)

eg. one Brazilian species pursues into their burrows

enfolds it

mouth exudes digestive enzymes that liquifies it

then sucks up liquified worm

eg.

terrestrial planarian common here

it also can eat small earthworms

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 17 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 18

Animal Parasites Costs to Parasite: the other classes of Platyhelminths contain only host is a small “discontinuous” habitat parasitic species parasite must locate and infect new hosts to propagate its species à most common form of must be able to overcome hosts defenses: 20-50% of all animal species are parasitic inflammation immune response 1/4th of all animal families are parasites but can’t kill host ectoparasites à parasite on outside of host à the most successful parasites do as little some can use gut for food storage and expand harm as possible to their hosts to many times their normal size eg. leeches, , Some Typical Endoparasitic endoparasite 1. Structures for penetration and attachment to à parasite lives on the inside of host host

digestive system often very simple or gone hooks, suckers, teeth, enzymes altogether most common point of entry to host is through mouth eg. tapeworms, flukes, roundworms 2. Usually have a resistant stage in life cycle Benefits to Endoparasitic Lifestyle: for getting from one host to another which is often in a different kind of environment constant environment if endoparasite - needs to survive trip through digestive system

gets easy access to food 3. Reduction in “unnecessary” structures

protection from predators reduced sense organs reduced nervous system reduced locomotion

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 19 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 20 reduced digestive system simplest life cycle: some endoparasites have lost gut entirely adult parasite à eggs à ingestion by new host some ectoparasites use gut mainly for food storage (eg. leeches, ticks) more complex life cycle: adult parasite à eggs à intermediate host à 4. Tendency toward being definitive host

only need any two, not male and female some can even self fertilize if necessaryà but usually don’t most complex life cycle: flukes have several intermediate states that reproduce 5. Enhancement of reproductive capacity 7. Behavioral Adaptations host is a small “discontinuous” habitat à need extraordinary powers of reproduction to insure behavior is an important tool for animal survival survival

reproductive organs are often the largest, most apparent organ this is also true for parasites: behavior can be systems present used to enhance their chances for success

often able to produce of large #’s of eggs (F. hepatica) à 20,000 eggs/day Examples: Ascaris à 200,000 eggs/day Tapeworm () 1. Simple host finding behaviors à 1M eggs/day for 15

(=5.5 trillion eggs/lifetime) eg. Entobdella (Monogenea)

skin parasite of a stingray 6. Use of intermediate larval stages on eggs are released and settle to bottom intermediate hosts larvae emerge from eggs within 3 seconds of sudden darkness à to enhance chances of getting to final host then swim vertically upwards

Even with large numbers of eggs chances of success are 2. Periodic Behaviors relatively small

eg. F. Hepatica parasite keys in on cyclic stimulus in most favorable situation 3-4 out of 20,000/day will actually eg. Filarial Worms hatch live in blood transmitted by or Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 21 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 22

larvae (microfilariae) move to peripheral blood on periodic basis Amphipods (fw ) typically hide in dark corresponds to “biting hours” of local vegetation during the day to avoid vector (flies & mosquitoes) when infected with acanthocephalan worm which as eg. Guinea worm adult infects , became highly photophilic and (: medinensis) conspicuous occur in tropical areas; lots of rice fields eggs must be laid in water to be able to get to its eg. burrowing clams infected with a fluke, intermediate host rather than burrowing into sediment, female may contain up to 1 Million eggs remain closer to surface where they are more likely to each with a developing larva inside be preyed upon larvae must be released in water to complete life cycle eg. Fluke () to do this female moves to part of body adult in birds; larva in likely to be immersed in water when infected, tend to crawl to tips of à lower legs vegetation instead of hiding like normal creates an ulcer in snail, larvae migrate to tentacles of snail at moment limb enters water the female larvae are brightly colored with red and green bands protrudes anus and discharges 1000’s of they pulsate infective larvae makes snails very conspicuous in daytime at night the larvae withdraw into the snails body 3. Host Modifying Behaviors eg. one of best adapted parasites known an alternative to modifying the parasites own Sacculina is a highly modified that has behavior is to alter the hosts behavior to become a parasite of crabs make it more likely to complete parasites as it matures it sheds all appendages, becomes an oval sac and penetrates a crab host life cycle develops an extensive system of branches extending into every appendage eg. (Tapeworm) a saclike growth appears under the crabs abdomen sheep infected with hydatid cysts lags behind healthier where eggs and sperm form (Sacculina is a members of heard à more easily caught and hermaphrodite) eaten by coyote the crabs is completely altered: b. Conspicuous Behavior if crab is female: changes are not as extensive but egg development is inhibited eg. Acanthocephalans: adult in birds (ducks); larva in if crab is a male: amphipods (small aquatic crustaceans) body assumes shape of a female Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 23 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 24 reduced length of some segments persistent poverty broadening of abdomen testes reduced or converted to ovaries decreased productivity

à both male and female resemble mature female poorer birth outcomes bearing eggs: physically and behaviorally decreased cognitive abilities, and neurological disorders Helminths malnutrition & anorexia

The most common endoparasites are flukes, tapeworms (classes of Platyhelminths) and roundworms

These three are grouped together as “helminths” (=parasitic worms) over 25% (1.5-2 Billion) of the world’s population is infected at any one time

that’s orders of magnitude greater infection rate as HIV

yet proportionally, helminth diseases receive only a small fraction of the research dollars

as such most are listed as “neglected tropical diseases” over 135,000 die each from helminth infections helminth infections also have considerable effects on:

overall health and tissue damage & inflammation, anemias

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 25 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 26

they feed aggressively on body fluids Class Trematoda can clog ducts and trigger gall stones and excessive enlargement over 3x’s more species than any of the other classes of liver of flatworms Body Wall

class includes some of our most serious parasites body covered by thin flexible cuticle

almost all are endoparasitic protects from hosts digestive enzymes

adults mainly found in integument is (not divided into individual

cells) with no cilia leaf-like body shape (=flukes)

muscle layers are embedded in “” two suckers for attachment:

Feeding & Digestion one around mouth

the other further down on the body like turbellaria, they have well developed, incomplete

digestive tract adults & larvae inhabit a wide variety of sites in

hosts: digestive tract àbut with mouth at anterior end respiratory tract gut usually divided into two branches urinary system reproductive system some dissolved nutrients can also be absorbed directly flukes tend to inflict greater harm to their hosts than through skin do tapeworms excretory and nervous systems similar to planarians flukes can be found in veins of intestines, bladder, bile ducts and Reproduction in high numbers they can cause blockages and damage most are monoecious and capable of self fertilization Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 27 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 28 transforms into …

sporocyst trematodes typically have a complex life cycle with sporocyst reproduces asexually (polyembryony) 1 or more larvae occurring in intermediate hosts yeilds more sporocysts or… and adults in definitive host redia also reproduces asexualy adults are typically parasites of fish or other produces more redia or… vertebrates cercaria emerge from snail 1 to 5 larvae occur in intermediate hosts, usually a penetrate second intermediate host mollusc or encyst in vegetaton to become…

metacercaria polyembryony occurs usually in several larval these are flukes stages allowing a single egg to develop into when eaten by definitive host develop into adult fluke 100’s of potential adults Some larval flukes are able to change hosts behavior typical life cycle: to make them more likely to get to final host:

eg. burrowing clams infected with a fluke, adult rather than burrowing into sediment, remain closer to surface where they are more likely to metacercaria egg be eaten

eg. Dicrocoelium (Trematode, Fluke) cercaria miracidium has 3 host life cycle:

adult in , eg sheep st redia sporocyst 1 larva in terrestrial snail nd 2 larva in eggs released by host are eaten by snail egg cercariae emerge entangled in slime of snail forming a usually passes in sticky ball must reach water to develop ants eat these slimy balls ants behavior changes so they are more conspicuous miracidium and more likely to be eaten by vertebrate: free swimming larva penetrates tissue of snail à when infected they crawl up blade of grass;

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 29 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 30

seize the grass in their and remain Examples of Flukes there until the next morning sheep are early grazers and eat the eg. (Chinese Liver Fluke)

eg. Fluke (Leucochloridium) adult in birds; larva in snail the most important human liver fluke when infected, snails tend to crawl to tips of vegetation instead of hiding like normal in snail, larvae migrate to tentacles of snail one of most complex life cycles: larvae are brightly colored with red and green bands they pulsate primary host and two intermediate hosts makes snails very conspicuous at night the larvae withdraw into the snails body during the day they are easy prey for birds 5 larval stages

serious problem in China, Asia, Japan

are final host (also cats, dogs, pigs) in which the adult lives

transmitted to humans by eating raw fish

Adult

10-20 mm long oval, with 2 ventral suckers simple digestive sacs hermaphrodite almost 80% of body is devoted to reproduction

flukes mature in intestine then move to bile ducts in liver

typically lives 15-30 years (up to 50 yrs) Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 31 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 32 eg. hepatica (Sheep Liver Fluke) light infection are asymptomatic or may produce light abdominal pain adult lives in liver and bile ducts of liver of sheep, other ruminants and can live in humans heavy infection (up to 20,000) can cause liver damage, cirrhosis and death feed on blood

1000’s of eggs released each day in feces into can produce up to 50,000 eggs/day for several water years

eggs can survive weeks in water eggs passed in feces

if snail eats egg miracidium larva hatches from if pasture is wet the eggs hatch into free living egg and developes into sporocyst then redia miracidium then cercaria

through polyembryony, a single egg can produce miracidium ingested by snail or penetrates land 250,000 cercaria snail and becomes sporocyst, then redia, then cercaria cercariae burst out of snail and burrow into fish and encyst in muscle as metacercariae through polyembryony, a single miracidium larva can produce up to 4000 cercaria larvae

if fish is eaten by the metacercaria cyst cercaria leaves snail and encysts as dissolves in intestine and fluke moves to liver metacercaria on vegetation of their adult host

when vegetation is eaten by sheep or ruminants, the adult hatches and moves to liver

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 33 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 34

eg. (blood fluke, ) female penetrates wall of blood vessel in liver and release eggs into bile ducts doesn’t occur in US; but >400,000 immigrants are infected eggs move from bile ducts to intestine and passed in feces one of the worlds major helminth infections eggs might also enter bladder and be released in urine à affects 200M worldwide: many eggs can lodge in liver and cause esp Africa, S. America, Mid East, Far East abdominal pain, fever and bloody diarrhea, ulcerations, etc 150,000 die each year from direct effects of eggs may also be carried to lungs causing inflammation the parasite; especially renal failure if eggs reach water they hatch into ciliated another 200,000 die from related causes miracidium

snail is intermediate host, humans are final host have only a few hours to find snail host or they die for 3 mainly human species if eaten by snail they develop into sporocyst,

then cercaria (no redia stage) other species of Schistosoma infect birds and

if humans are in contaminated water:

cercariae bore directly thru skin to get into mature adults live in portal vein of liver, feeding blood on blood

cercaria are one of few parasites that can bore through skin differ from most other flukes by being dioecious (separate sexed) rice farmers are easily infected

males larger in North America some blood flukes of birds may

females smaller, stay in groove (=gynecophoric canal) in atempt to bore into humans males body they don’t survive and cannot infect us

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 35 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 36 but their burrowing and death in skin can eg. ( fluke) cause swimmers itch lives in lungs of host

many mammals are hosts

found in East Asia, SW Pacific and parts of S. America

eggs coughed up, swallowed then eliminated in feces

metacercaria develop in fw crabs

infection is acquired by eating uncooked crab meat

infection causes breathing difficulties and chronic cough

fatalities are common

one species found in N America infects minks with its larvae in crayfish

only 1 human case reported

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 37 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 38

Class Monogenea egg hatches into ciliated larva A group of small (rarely >.75”) mostly ectoparasitic flatworms larva and adult have large posterior attachment organ with hooks widespread and common

1000’s of species once placed with trematodes all are parasites

àmainly ectoparasites on gills or skin of fish

some species infect other cold blooded animals

one species infects the of hippos, no other warmblooded birds or mammals a few are found in urinary bladder of and turtles have anterior and posterior attachment organs seem to cause little damage to their hosts all are hermaphrodites direct life cycle with single host

they have no intermediate hosts

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 39 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 40 Class Cestoda (Tapeworms) proglottids bud off the scolex >1000 species (a chain of proglottids = strobila) most specialized class of flatworms bud from scolex with oldest ones furthest all are endoparasites away

à not same as segmentation since each proglottid acts can grow up to 10 M (30’) long as an individual animal

1991: doctors removed 37’ tapeworm from Mississippi woman

max tapeworm length ever recorded is over 90’ taken from some individuals can produce a dozen a sperm whales intestine proglottids/day

adult can live up to 20 years some tapeworms have up to 3000 proglottids

Body Plan Body Wall

very different from other classes of flatworms tegument is syncytial (not subdivided into separate

cells) with microvilli (microtrichs) to increase àno head surface area for absorption

front end of the animal is not a head, it’s a tegument secretes a protective cuticle special organ for attachment (=scolex)

no external cilia à has suckers and hooks

well developed muscle layers beneath body wall use for attachment, not for feeding or sensing

the environment Feeding & Digestion

à“body” consists of a long chain of reproductive completely lack digestive system sacs = proglottids

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 41 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 42

à absorb food through skin (=tegument) typically the intermediate host is the prey of the Nervous System adult host simple nervous system all are monoecious (hermaphrodites) proglottids are united by nerve cords, the most mature proglottids are those furthest away from the scolex but no special sense organs unlike most hermaphrodites, tapeworm proglottids can Excretion cross fertilize in same animal somewhat similar to other flatworms testes usually develop before ovaries so generally can self- fertilize a single proglottid

protonephridia continuous throughout proglottids eggs or mature proglottids are shed in feces

Reproduction & Life Cycles once egg is released must be ingested by intermediate host (another vertebrate) each proglottid acts as “individual” à usually a vertebrate “prey” of a final host à any two proglottids can exchange sperm once eggs ingested larva hatches and bores through when gravid each proglottid may contain up to intestines of host and into blood 100,000 eggs each travels to , heart and other organ Life Cycle secretes a protective cyst almost all tapeworms require at least 2 hosts; mainly vertebrates in some, cyst develops into a “bladder-worm” or cysticercus but same host can bear either the adult or the larval parasite Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 43 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 44 humans can get infected with eggs by unsanitary Examples of Tapeworms habits with feces, not washing hands, kissing pets, etc eg. Beef Tapeworms ( saginata)

but humans make poor intermediate hosts from >50 Million infection worldwide; especially South the parasites perspective America, SE Asia, Africa

à nothing eats them adult in human intestine

mature adult may reach 10 M (30 ft) or more

scolex buries itself in intestinal wall

à has 4 suckers to attach (no hooks)

can bud over 2000 proglottids

numerous proglottids are released each day:

gravid proglottids break off and pass with feces

sometimes they crawl out anus

they crawl out of feces into nearby vegetation

proglottids dry and release eggs

à can remain viable on grass up to 5 months

picked up by grazing cattle

when eaten by cattle the eggs hatch Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 45 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 46

larva burrows through intestine and into blood eg. Pork Tapeworm ()

reach skeletal muscles where they encyst as pork tapeworm is more dangerous to humans bladderworms since the larval stage can more easily develop in humans = “measly meat” adults usually live in human In US infections are not uncommon: juvenile in muscles of pigs

34 M cattle in US; ~1% of US cattle are infected 20% not federally inspected adult can live up to 10 years and grow to 10’ long th 1/4 of the infections are missed in inspection of meat generally doesn’t occur in US but thrives in Mexico à 5 in 10,000 or ~150,000 in US infected and Central America

humans become infected by eating ‘rare’ or poorly occasionally shows up along border. cooked roast beef, steaks and barbecues WHO estimates that 2.5 Million are infected with

adult worm and many more with larvae when measly meat is eaten bladderworm hatches worldwide and adult develops in intestine of final host

takes 2-3 weeks for mature worm to develop scolex has hooks and suckers

if just a few the infection will be mild or life cycle is similar to beef tapeworm asymptomatic each proglottid can release 50,000 eggs light infections may cause weight loss eggs eaten by pigs and larva migrates to skeletal à “diet pills” muscles

heavier infections may cause diarrhea and humans usually infected by eating poorly cooked vomiting pork and adult develops in intestine

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 47 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 48 eg. Echinococcus (dog tapeworm)

if humans ingest eggs rather than the larva about 1 Million are infected worldwide.

the eggs will develop into a bladderworm that one of the most dangerous tapeworms encysts in body tissues a group called “tissue tapeworms” = adult is very small: only a few mm can cause serious problems by lodging in: adults occur in dogs, coyotes, wolves and other eyes à blindness canines

brain à neurological symptoms or death juvenile develops in >40 species of mammals muscle à pain and weakness, inflammation (eg. monkeys, sheep, reindeer, cattle)

and other visceral organs including humans

treatment usually involves surgery sheep infected with juvenile lag behind healthier members of heard à more easily caught and eaten by coyote

humans can become intermediate hosts by fecal-oral route; eg. kissing pets

(humans are dead end choice for parasite since few eat humans)

once ingested, juvenile moves to various tissues; eg. liver, lungs, brain

juvenile stage is special kind of cysticercus = hydatid cyst

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 49 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 50

eg. Fish Tapeworm (Diphyllobothrium latum)

grows quickly; 1 cm/month, for up to 20 years humans and other animals are definitive host

may be no symptoms for years ocurs wherever fish are an important food source and the water supply is easily can reach size of basketball contaminated with sewage

à up to 4 gallons endemic in Europe, Asia, US &

within main cyst daughter cysts bud off 2 intermediate hosts: & fish

each daughter cyst contains 1000’s of in humans, adult attaches to intestinal lining by scolices scolex (no hooks)

symptoms and signs depend on the cyst’s eggs are released in feces location and size if feces enters water eggs may be eaten by tiny in humans, growth of cyst can cause damage to , organ fish eats copepod and bladderworm encysts in fish if cyst ruptures the fluid itself can produce muscle anaphylactic shock, even death if fish are improperly cooked, or eaten raw (sushi) only treatment is surgical removal the infection is transferred to humans

thorough cooking or freezing (-10º C) for 24 hrs kills the parasite

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 51 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 52 eg. Diphylidium caninum Human Costs of Parasitic Flatworms

adult in small intestine of dog or cat 250-300 Million people worldwide are infected with some type of parasitic up to 6” long (some put that number much higher) fleas are intermediate host results in Billions of dollars in healthcare costs and lost fleas eat tapeworm eggs released in pet feces productivity

egg hatches and encysts in also affects and pets

dog eats fleas and bladderworm hatches into adult Beneficial Effects of Parasitic Flatworms

1. weight loss

light infections of adult tapeworms cause little damage and may cause a loss in weight

à larvae once sold as weight loss pills in US

today the treatment is only available in Mexico, the approximate cost is $1500.

tapeworm infestation can result in a loss of one to two pounds per week.

once the target weight loss is reached, a deworming agent is given

Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 53 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 54

However, Tapeworm infestation can result in: à as hygiene has improved allergies, asthma and The formation of cysts in the liver, eyes, brain, other autoimmune diseases have dramatically and spinal cord with potentially lethal increased consequences. in developed countries, where improved sanitation if pork tapeworm much more serious has largely eliminated helminth infections there has been an increase in such intestinal blockages autoimmune disease in the past 100 years

malnutrition these same diseases are rare in poor countries where intestinal parasites are endemic 2. Helminth Therapy there is a large “underground market” in helminth a type of immunotherapy to treat autoimmune parasites fueled by these findings – medicine is diseases and immune disorders by deliberately just now catching up infecting patient with intestinal parasites research has found that intestinal parasites, particularly roundworms have the ability to temper the and prevent the overreactions that cause allergies, asthma, ulcerative colitis, Chron’s disease, etc helminthes have thrived in mammals for millions of years over that time they have adapted to survive the onslaught of the hosts immune responses to the infection

“Hygiene Hypothesis” Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 55 Animals - Animal Phyla: Phylum Platyhelminthes; Ziser Lecture Notes, 2015.10 56