Phylum Platyhelminthes
= Life in 2 dimensions, i.e. the flatworms
General Platyhelminth Characteristics
Triploblastic
Acoelomate
Bilateral
Vermiform bodyplan =
dorsoventrally flattened
Not generally segmented,
exception = tapeworms
Distinct cephalization
Protonephridia
Incomplete gut
Platyhelminth General Body Plan
Sperm duct
Dors. Muscle
Circ. Muscle
Long. Muscle
Gut
Testes
Flame
cells
Vitellaria
Oviduct
Nerve cords
Epithelium - Multiciliated cells, mucous secretory cells,
rhabdites (Turbellarians) = mucous coated, syncytial tegument
= parasites
Muscle layers - Longitudinal, circular, oblique
Mesoderm - network of irregular shaped cells, support to
internal organs, no body cavity
Nutrition/ Gut Cavity
Carnivorous
= predators, scavengers,
parasites, detrital feeders
Gut structures
Acoels = lack permanent gut
cavity
Rhabdocoela/Allocoela = 1
branched gut
Triclads = 3 branched gut
Polyclads = multi-branched
gut
Nutrient diffusion
Excretion/ Osmoregulation
Diffusion = ammonia removal
Protonephridia =
excretion/osmoregulation
nephridiopore
Locomotion/ Attachment
1. Ciliary gliding
2. Swimming
Attachment
1. To sand grains (temporary)
2. Duogland adhesive
a) Viscid and b) Release
3. Suckers
a) Oral and b) Ventral
4. Scolex
5. Hooks
Nervous System/Sense Organs
Orthogon =ladder like plan
= longitudinal nc’s connecting to
transverse ring
=> make space for parasitic lifestyle
Anterior concentration = ganglion
Ocelli, chemoreceptors
Reproduction
1. Sexual
Monoecious (hermaphrodites)
Cross-ferilization
= reciprocal or one way
- hypodermic insemination
- = no female opening
- Internal fertilization =
release of encapsulated
eggs
- Juvenile of Mueller’s larva
- Miracidium, rediae,
cercariae
- 2. Asexual
Transverse fission
Classification
Class Turbellaria
=free living or commensal
Rhabdites, cilieated epidermis
No attachment, but sensory structures
Class Aspidocotylea
Ventral suckerlets
Classification
Class Cestoda
= the tapeworms
Elongated endoparasites, proglottids
No alimentary canal
Class Trematoda
Ecto- or endoparasites
Undivided body
Well developed
attachment organs
2 or more hosts