Read Worms by Body Plan and Life Cycle
Worm groups differ in body cavity and form, while parasitic species often use specialised attachment and multi-host life cycles.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Separate roundworms and flatworms
Nematodes are cylindrical pseudocoelomates with separate sexes in many species; female Wuchereria is larger than the male. Platyhelminthes are flattened acoelomates, often hermaphroditic, with flame-cell protonephridia; parasitic forms may have hooks/suckers and absorb nutrients through the body surface.
Follow a trematode cycle
A trematode may pass from eggs to a ciliated miracidium, then a snail, cercariae, a second intermediate host and an encysted stage before reaching the bird definitive host. Amphibian infection can cause extra limbs, increasing predation and parasite transmission.
Link host manipulation to transmission
A trematode moves through snail and tadpole hosts before reaching its definitive bird host. Extra limbs make tadpoles easier for birds to catch, helping the parasite reach that final host. The snail is not the final host. Choose B and C.
OlympIQ exam lens
- ✓Nematode: pseudocoelom, cylindrical, sexes often separate.
- ✓Flatworm: acoelomate, flattened; flame cells.
- ✓Trematodes often use multiple hosts and larval stages.
- ✓Parasite-induced host changes can increase transmission to the definitive host.
Do not confuse a pseudocoelomate roundworm with an acoelomate flatworm.
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