Platyhelminthes

Flatworms

Tapeworms

Flukes

PHYLUM PLATYHELMINTHES

• Bilateral

• Triploblastic

• Acoelomate– Gastrovascular cavity

• Cephalization

• Ladder-like nervous system

• Protonephridia with flame cells

Fig. 21.15

Symmetry

Traditional View Continues

• Acoelomate - Pseudocoelomate vs Coelomate

Aceolomate no space between tissue layers,

no cavity

• Protonephridia with Flame cells

Class Turbellaria

• Free living flatworms

• Example: Dugesia (Planaria)

External Anatomy

• Ladder-like nervous system

• No real “brain”, but anterior ganglia

Ladder Nervous System

Fig. 21.18

Planaria c.s.

Class Trematoda

• Flukes

• All parasitic

• Possess two suckers

• Have complex life cycles

• Need multiple hosts

Chlornorchis sinensis

Fasciola hepatica w.m.

Schistosoma sp. w.m.

Schistosomiasis

eosinophylls attacking a larval fluke.

Class Cestoda

• Tapeworms

• Scolex and proglottids

• Segmented

Diplydium caninum

Scolex Anatomy

Rostellum

Suckers

Neck

Tapeworm development

Proglottid anatomy

• Uterus

• Genital pore

• Ovary

• Testis

Echinococcus granulosus w.m.

Hydatid cyst

• Capsules of scolices

Hydatid Cyst Disease