PLATYHELMINTHES(Flatworms)

GENERAL CHARACTERISTICS

• Morphology– Flattened dorso-ventral– No segmentation, bilaterlly symetrical– Incomplete GIT( no anus) – Lack body cavity– Hermaphrodite or monoecious

• EXCEPT for Schistosoma (dioecious)

PLATYHELMINTHES: CHARACTERISTICS

• 3 dermal layers (tripoblastik)• Flat dorsal –ventrally• Dorsal different from ventral• Anterior different from posterior• Mouth and genital opening on ventral side• Bilateral symmetry• Considered most primitive animal• Living surface membrane• No body cavity except for digestive tract (acoelomate).

Space between organs filled with parenchyma cells (a kind of connective tissue)

PLATYHELMINTHES: Characteristics (cont.)

• Considered more advance than Cnidaria because they have developed good nervous, muscle and reproductive systems;

• Do not have an anus; wastes remove through mouth; • Nervous system made up of a pair of anterior ganglion and

longitudinal nerve cord and connected with a criss-cross of nerve network;

• Simple sensory organ; eye-spot for some;• Excretory system made up of 2 lateral canals with

branching ending in the flame cells (protonephridia). Absent in the primitive forms.

PLATYHELMINTHES: Characteristics (cont.)

• Respiratory, circulatory and skeletal systems absent; • Most monoecious. ie. both male and female organs on

same animal; • Asexual reproduction also possible - regenaration.

PHYLUM PLATYHELMINTHES – FLAT WORMS

PLATYHELMINTHES: CLASSIFICATION

• Class Terbullaria (free-living)• Class Monogenea• Class Trematoda (flukes)• Class Cestoidea (tape worm)

Classification

Class trematoda (Flukes)– Liver flukes

• Fasciola hepatica• Chlonorchis

sinensis– Intestinal flukes

• Fascilopsis buski– Lung flukes

• Paragonimous westermani

– Blood flukes• Schistosoma sp.

Class Cestoda– Order

Pseudophyllidea• Diphylliobotrium

latum

– Order Cyclophyllidea• Dipyliidium

caninum• Hymenolepsis nana• Taenia saginata• Taenia solium

Internal sections of a Planaria

Class Terbullaria

• Most free-living• Found in the oceans, in fresh water, and in moist

terrestrial habitats, and a few are parasitic • Most are carnivorous;• Some omnivorous;• Excretory system made up of 2 lateral canals with

branchings that end in flame cells (protonephridia).– eg. Planaria

Eg. planaria Dugesia sp

Protonephridia (flame cells)

• Function more for osmoregulation

• Excess water (and waste materials) absorbed into flame cells;

• Materials moved along excretory canal by cilia movement to be discharged via excretory pore

Flame cell (protonephridia)

Excretory canal

Flat worm – external features

A    Dorsal surfaceB Dorsal and ventral surface; 1    Head 2    Anterior 3    Posterior 4    eye-spot 5    Sensory lobe 6  Dorsal surface7 Mouth 8    Pharynx (extended when feeding) 9    Pharynx opening10    Genital opening11    Ventral surface (ciliated)       

CLASS MONOGENEA

Parasites found in gills skin of fish. Never in humans

CLASS TREMATODA

Class Trematoda:

– All parasites, especially along digestive tract;• Digenea – 2 host, one must be mollusca• Aspidogastrea -1 host, normally mollusca• Didymozoidea – in fish tissue

Life Cycle of Liver Fluke - Trematoda

CLASS CESTOIDEA(tape worm)

Class Cestoda: Taenia sp. – tape worm found in pork

Scolex

Hook

Sucker