Worms- Phylum
Platyhelminthes
LINK TO VIDEO
Flatworms - General Information
3 phyla in Ch. 14 – We are going to focus mainly on Phylum Platyhelminthes
Symmetry: Bilateral
Cephalization- head end concentrated with sense organs and nervous
control
Tripoblastic- has a middle germ layer (mesoderm) as well as ectoderm and
endoderm
Parasitic in nature
Examples of Flatworms include: planaria, flukes, and tapeworms
4 Classes : Turbellaria(Planarians), Trematoda (Flukes), Monogenea and
Cestoda(Tapeworms)
Class: Turbellians - Body Form
•Ciliated epidermis
•Rod- shaped Rhabdites- swell and form a protective mucous
sheath around the body
•Dual gland adhesive organs in the epidermis
Class Monogenea, Tremotoda, and
Cestoda – Body form
Parasitic
Non-ciliated body covering
Ciliated covering is lost once a host is contacted
Digestive System:
Includes a mouth, pharynx, and an intestine
GVC- Gastrovascular cavity present
Mainly carnivorous – feed on small crustaceons, nematodes, rotifers, and insects
Flatworms have a system called: protonephridia/ can be used for osmoregulation or excretion
System is mainly osmoregulatory ( regulates the water inside and outside of the body)
Flame Cells- cup shaped cell that has flagella extending out
Nervous SystemSimple nervous system (found in turbellarians) – Subepidermal Nerve Plexus similar to the nerve net
in cnidarians
•May also have one to five pairs on longitudinal nerve cords lying under the muscle layer
•Have ganglia and neurons
•SENSE ORGANS:
•Ocelli: light sensitive eyespots
•Tactile Cells -touch
•Chemoreceptive cells •Statocysts for equilibrium
•Rheorecptors- sensing direction in water currents
Reproduction and regeneration:
Reproduce both sexually and asexually (fission) same as budding like
the hydra
Almost all flatworms are monoecious
Some have spiral determinate cleavage typical of protostomes
Class Turbellaria – extra information
Often distinguished on the basis of the form of the gut (
present or absent? , simple or branched?, pattern of
branching? )
•Creeping forms that combine muscular with ciliary
movements to move
Class Trematoda
All parasitic flukes
Leaflike in form
Penetration glands / organs for adhesion to hosts like suckers and hooks
Increased reproduction capacity
Sense organs are poorly developed
EX: Liver Fluke in Humans ( common in regions of east Asia, especially China,
Southeast Asia, and Japan; also common in cats, dogs, and pigs.)
Blood Fluke (causes schistosomiasis)
Life cycle of a fluke
Class Monogenea
Are all parasites ( on fish, frogs, turtles, and one on the eye
of a hippopotamus)
Cause little damage to hosts
Can be serious if many hosts are crowded together (farmraised fish)
Class CestodaTapeworms
Long, flat bodies
Has a scolex(for attachment to host)- has suckers/ tentacles for attachment , and
proglottids ( linear series of reproductive units)
No digestive system
Well-developed muscles
Excretory system is similar to other flatworms as well as nervous system
No special sense organs
No head
Examples of Cestoda : Beef Tapeworm, Pork Tapeworm, Fish tapeworm, Dog Tapeworm
Phylum Nemertea
Often called ribbon worms
Long muscular proboscis
Bilateral
Triploblastic
1000 species; all marine
Annelids
link
Ch. 17 P. Annelida
•Segmented Worms – Each segment contains similar
components of all major organ systems
•Annuli- Circular Rings that give this phylum their name
•Setae- Chitinous bristles ( exception: leeches) Eww!
•Freshwater dwelling – Oligochaetes (Earthworms and
Leeches)
Body Plan
Two part head region - Prostomium and Peristomium
Terminal portion: pygidium which contains an anus
Each segment contains: 1) circulatory, 2) respiratory, 3)
nervous, 4) Excretory 5) coelom
Peritoneum lines the body wall of each compartment
Hydrostatic Skeleton: coelom is filled with fluid
Triploblastic- 3 Germ Layers
Coelom well developed
Bilateral symmetry
Nervous System: double ventral nerve cord, ganglia, Brain
Sensory system: Tactile (touch) organs, taste buds,
photoreceptor cells
Reproduction Methods
Asexually by fission
Can completely regenerate
Sexually- Monoecious – having both male and female
organs
2 Classes have Clitellum( region of body) which aids in
sexual reproduction
3 Classes:
1)
C. Oligochaeta
2) C. Hirundinida –Leeches
3) C. Polychaeta ( paraphyletic group) What does THAT
mean?
Groups 1 and 3 share a common feature:
Reproductive structure called a clitellum
Environments:
Marine, Freshwater, and Land (terrestrial)
Class Oligochaeta:
See terms on vocabulary sheet