Platyhelminthes & Mollusks

Question 0

General Anatomy of Flatworm

Answer 0

• Specialized organs
• Nervous organization
   – Longitudinal & lateral branching 
      nerves to brain
• Gastrovascular cavity
• Cephalization
   – definite head region 1st time
• Eyespots
   – Area on head; light sensitive but 
     doesn't form images
• Auricle 
   – Lateral projection
   – Sensitive to touch & chemicals
• Hermaphroditic
• Acoelomate
• Bilateral symmetry = triplobastic
• Sac

Question 1

Phylum Platyhelminthes

Answer 1

• Flatworms
• Acoelomate (no body cavity)
• Gastrovascular cavity
   – Mouth is also anus
   – Digestion is extracellular & 
      intracellular in 3-branched blind 
      cavity

Three classes

(1) Turbullaria
– Free living (planaria, dugesia)

(2) Trematoda
– Internal parasites (Flukes)

(3) Cestoda
– Digestive parasites (tapeworms)

Question 2

Class: Turbullaria (planaria)
Phylum: Platyhelminthes

Answer 2

• Digestion: Gastrovascular cavity
• Circulation: Gastrovascular cavity
• Nervous: Brain, 2ventral nerve cords, 
                  ladder-like
• Habitat: Aquatic
• Respiration: Diffusion
• Excretion: Flame cells
• Locomotion: Muscles
• Support: None
• Reproduction: Hermaphroditic

Question 3

Class: Trematoda (flukes)
Phylum: Platyhelminthes

Answer 3

• Internal parasites
• Complex life-cycles w/ intermediate
hosts

Question 4

Class: Cestoda (tapeworms)
Phylum: Platyhelminthes

Answer 4

• Digestive parasites

Question 5

Phylum Nematoda

Answer 5

• Unsegmented roundworms
• Free-living
• Environments: Aquatic, deserts, 
   damp soil, hot springs & cider 
   vinegar
• Bilateral symmetry
• Psuedocoelomate
• Longitudinal muscles only
• Whip-like movement
• Complete digestive system
• Gonochoristic: 
    – Separate males & females
    – Males have posterior hook
• Nervous organization:
    – Brain, dorsal, ventral & lateral 
       nerves

Question 6

Phylum Rotifera

Answer 6

• "Wheel animals"
• Mostly freshwater planktonic animals
• Psuedocoelomate, triplobastic
• Corona
   – Ciliated organs to move & feed
• Mastax to crush food
• Excretion: flame cells

Three general regions:
• Head
• Trunk
• Posterior foot