Transcript Phylum Platyhelminthes ("flatworms")

Worm Phyla:
Platyhelminthes (flatworms - acoelomates)
Nematoda (roundworms - pseudocoelomates)
Annelida (segmented worms – coelomates)
Phylum #1
Platyhelminthes
(flatworms)
Classes:
1. Turbellaria (free-living)
2. Trematoda (parasitic)
3. Cestoda (parasitic)
Phylum Platyhelminthes ("flatworms")
Evolved from Cnidarians, gained bilateral
symmetry and developed excretory, nervous and
reproductive systems. Bilateral, acoelomates.
Digestion = single opening (mouth and pharnyx)
and digestive cavity. Excretory = flame cells
excrete wastes. No circulatory or respiratory
systems; diffusion only for O2 / CO2 exchange.
Sexual (hermaphrodites) and asexual
reproduction regeneration.
Class #1
Turbellaria
(Phylum Platyhelminthes)
 free-living scavengers
 branched intestines with pharynx tube
 eyespots, can learn (chopped up & fed to others...)
 hermaphroditic; sexually reproduce
A variety of
marine
turbellarians
Eurylepta
This turbellarian flatworm mimics a (very unsavory) sea slug
Marine Flatworms mating
Class #2
Trematoda - flukes
(Still Phylum Platyhelminthes)
 Parasitic (species-specific)
 Thick, protective "tegument" resists acids/enzymes
 No digestive system (diffusion only for gases / food) no
eyespots; very little cephalization
Ex: Swimmer's itch, Schistosoma, Liver flukes
Sheep liver fluke
Sheep livers with trematode fluke
Schistosoma
male/female
Schistosoma
male / female
blood flukes
Typical Schistosoma egg
Schistosome eggs, which may become lodged within
the hosts intestinal wall or in liver, are the major
cause of pathology in schistosomiasis.
Class # 3
Cestoda (tapeworms)
(still Phylum Platyhelminthes)
• parasites (mostly mild symptoms in wellnourished people)
 scolex (head with hooks)
 proglottids (egg cases)
Ex: Diplydium (cat intestines  feces  larval fleas 
adult fleas  another cat  ingested by licking fur)
Scolex of tapeworm
Nereis
closeup
Methane hydrate deposits on the ocean floor teem with
life. Residents include ferocious polychaete ice worms
that burrow into the formations and defend their lairs
against intruders.
Tapeworm (Class Cestoda)
•Scolex and proglottids
Phylum Nematodes
(roundworms)
Evolution- gained body cavity
(pseudocoelom), separate sexes, and
complete digestive system (2 openings).
Bilateral symmetry. Dioeciuos– not
hermaphrodites. Complete digestive system
(two openings). Circulation and respiration
through diffusion.
Nematodes are pseudocoelomates
DISEASES
Pinworm (Enterobius sp.): eggs swallowed (dust/food)  lg.
intestine (lay eggs)  anus (itching)
Lungworm (Ascaris sp.): eggs swallowed  penetrate to
lungs  throat  swallowed  intestine (lay eggs)
Trichinosis: cysts ingested (pork, bear)  intestine (pain,
diarrhea, fever)  blood  muscles (lumps, pain)
Hookworm (Huck Finn disease): bloodstream  push
abdomen through intestine  eggs outside
Brainworms, heartworms, Guinea worms (“the fiery
serpent” makes great tattoos!), Filaria (clog lymph:
elephantiasis), Loa loa (eyeworms)
The Fiery Serpent- Guinea Worm
Trichina-- a roundworm (nematode) common in pork
• picture shows capsule embedded in muscle tissue.
• enters host via raw or poorly cooked meat
• eggs shed in the gastrointestinal tract--> feces
• eggs eaten by herbivores --> encyst in muscle
• encysted worm is resistant to antihelmithic drugs.
Heartworm-a parasitic
nematode
Pinworms-- infections of kids (itchy eggs!)
Reminder: Kingdom Animalia; Phylum Nematoda
Phylum Annelida The Segmented
Worms
Evolution-development of coelom.
Cephalization! Well-developed nervous system: nerve cord with
ganglion in each segment and anterior brain
Bilaterally symmetrical
Organs within a true coelom (cavity within mesoderm)
Compartmentalization of organs / movement of parts of body
Closed circulatory system with five pairs of “aortic arches”
Most have red hemoglobin in blood (efficient) Sophisticated
digestive system:
mouth  pharynx esophagus  crop gizzard  intestine  anus
Appendages: Setae &/or parapodia
Excretion- Nephridia remove nitrogenous wastes; wets skin
Respiration—use diffusion
Most hermaphroditic, some dioecious.
Classes of Annelids
Oligochaeta: earthworms, nightcrawlers, (aquatic) tubifex worms
 20-45 tons of soil/year/acre processed by worms on organic farms
 each worm processes its own weight each day
Polychaeta: bristleworms, tube worms, featherdusters
marine worms with parapodia and (most) jaws!
Hirudinea: terrestrial / aquatic leeches
some parasitic, some free-living
•medicinal anticoagulant “hirudin”
Fanworm
A filter-feeding polychaete:
feather-duster
Bristle-worm (nereis)
The medicinal leech is best known as the organism used
for blood letting (people used to believe many health
problems caused by "bad" blood). They are being used
once again to remove blood from hematomas (areas of
blood leakage) resulting from surgery (like re-attaching
severed limbs, etc.).
http://www.sp.uconn.edu/~mcbstaff/
graf/AvHm/MedUsemain.htm