Platyhelminthes

Question 1

General Characteristics (7)

Answer 1

Bilateral symmetry, triploblastic, cephalization
Acoelomate
Gut with one opening (GVC)
Dorso-ventrally flattened
Cerebral ganglia (brain) & long. nerve cords (anterior)
Protonephridia - excretion & osmoregulation
Hermaphroditic, internal fertilization, complex reproductive system

Question 2

Free-living flatworms (Turbellaria)
Basic Anatomy
Feeding, circulation & gas exchange 
Locomotion
Nervous System 
Osmoregulation & Excretion
Reproduction

Answer 2

Bilateral, cephalization, gut with one opening
Mid-ventral mouth (often with protrudable pharynx)
Scavengers/predators: secrete digestive enzymes or swallow prey whole (some have neurotoxins)
Ciliary-mucus crawling, muscular undulations for swimming/crawling
Cerebral ganglia, longitudinal nerve cords, peripheral nerve plexus
Protonephridia for osmoregulation and excretion of ammonia
Asexual – transverse fission planes
Sexual – hermaphroditic, internal fertilization, complex male & female reproductive systems

Question 3

Adaptations for Endoparasitism (7)

Answer 3

Loss of cilia & reduction of musculature
Reduction of sensory structures 
Nutrient Absorption
Resist host defences 
Complex life cycles: definitive/intermediate hosts 
Many eggs
Polyembryony

Question 4

Class Trematoda

Morphology

Answer 4

Mouth with oral sucker 
Muscular pharynx 
Ventral sucker
Intestinal caeca
Uterus, ovary, testes, seminal receptacle & yolk glands

Question 5

Class Trematoda Life Cycle (Clonorchis sinensis)

Answer 5

The definitive host (human) has adult worms in bile ducts
Eggs passed out in feces and eaten by a snail
Forms a miracidium which develops into a sporocyst
Sporocysts undergo polyembryony to form many rediae. Rediae undergoes polyembryony to form many cercariae that rupture.
Cercariae swim to fish and encyst as metacercariae then eaten by a human

Question 6

Schistosome parasite

Answer 6

Snail as an intermediate host

Cercariae invade definitive host

Question 7

Class Cestoda Morphology

Answer 7

Scolex (head area) has anterior hooks and 4 anterior suckers

Budding neck zone followed by many replicate proglottids

Question 8

Class Cestoda Life Cycle (Taenia)

Answer 8

Carnivore with an adult worm in the small intestine
Proglottids deposited in feces
Herbivore eats oncosphere
Develops into cysticercus within the muscle
Eaten by a carnivore