Acoelomate and Pseudocoelomate Animals

Question 1

What are the defining characters of Platyhelminthes?

Answer 1

1. Active, directed movement
2. Cephalization and bilateral symmetry
3. Triploblastic, acoelomate
4. Body dorsoventrally flattened
5. Tissues organized into organs (incomplete digestive system/blind gut, gas exchange by diffusion thru body surface, excretory system with protonephridia, muscular and nervous system better developed, both asexual and sexual reproduction. Mostly monoecious but practice cross-fertilization)
6. Both free living and parasitic forms
7. Aquatic or in moist terrestrial habitats

Question 2

What are the advancements shown by Platyhelminthes over Cnidarians?

Answer 2

1. Actively move, triploblastic, flattened body for more surface area for diffusion, possession of a brain

Question 3

What are the important features in the life cycle of the medically important parasites, blood fluke, liver fluke and tapeworm?

Answer 3

1. Organs for attachment
2. Ability to form stages that can survive harsh conditions
3. Poorly developed digestive system
4. High reproductive capacity

Question 4

Name some adaptations for parasitic life (that you also see in flatworms)

Answer 4

1. Possess nervous and digestive systems
2. Larger surface area
3. Hermaphrodytic

Question 5

What are the defining features of nematode worms? What advancements do they show over flatworms?

Answer 5

1. Cylindrical with thick, flexible cuticle (roundworms)
2. Pseudocoelom used as a hydrostatic skeleton for movement. A space for organs, although they are still not well anchored in this cavity.
3. Complete digestive system
4. Sexes usually separate (dioecious)
5. Many show utely, a condition in which the number of cells is constant for the entire animal.
6. Both free-living and parasitic forms. Most microscopic.
7. Mostly freshwater, abundant
8. Important in terms of their netrient recycling ability and impact on health.

Question 6

Which are some of the medically important nematode parasites and what are some of the important features in their life cycle?

Answer 6

Ascaris (intestinal roundworm), Enterobius (pinworm), Necator (hookworm, causes anemia), Trichinella (porkworm), Wuchereria (filarial worm), Dirofilaria (Heartworm of dogs)

• Larvae deposited in feces or mucosa
• Adults attach to intestines, etc.
• Parasites are either ingested, penetrate the skin, or are transferred via another host