February 14, 2001

1
Lecture 11

• February 14, 2001
• Chapter 18
• The Evolution of Animal Diversity

2
Learning Objectives

• Contrast psuedocoelom and coelom
• Contrast the body plan of flatworms, roundworms,
  and segmented worms
• Name two mammalian diseases caused by nematodes
  (roundworms)
• Recite the 3 major classes of molluscs
• Arrange the phyla covered so far by increasing
  complexity

3
Question Who is the Simplest Phylum?

• Choose one
• Cnidaria
• Mollusca
• Nematoda
• Platyhelminthes
• Porifera

4
Psuedocoelom and Coelom

• These are body cavities
• A body cavity allows for
• Flexibility
• Organ protection
• Improved movement (muscles can work against
  hydroskeleton)
• Fluid can move nutrients, O2, metabollic wastes

5
Why Have a Hydroskeleton?

• Muscles only pullthey cannot push
• A flatworm is small, can move around by thrashing
  in liquid environment
• How then, can an earthworm move its head forward?

6
Flatworm Body Plan

• Has solid body
• No body cavity

7
Roundworm Body Plan

• Has a pseudocoelom
• Basically, the open space between muscles and
  digestive tract

8
Earthworm Body Plan

• Has a true coelom
• Surrounded by muscle tissue

9
Comparison
10
Roundworms

• Phylum Nematoda
• Have a complete digestive system
• Both mouth and anus
• Allows for 1 way movement of food
• Cells in digestive tract can then specialize
• Cells in the front can mash, digest food
• Cell in the rear can absorb

11
Roundworm Life History

• Most are free-living
• A few are parasitic
• Heartworms in dogs
• Trichinella spiralis in humans
• Causes trichinosis!
• Worms find way into muscles
• Very painful, can be fatal
• From undercooked pork!

12
7th Inning Stretch
13
The Molluscs

• Phylum Mollusca
• 3 Classes (names have Greek roots)
• Gastropods (stomach foot)
• Snails
• Bivalves (2 opening doors)
• Clams, oysters, mussels, scallops
• Cephalopods (head foot)
• Octopi, squid

14
All Molluscs Have

• A true coelom
• Mucular foot
• Mantle
• In snails clams, produces a shell
• Mantle cavity can also hold a gill or a lung!
• Many molluscs also have a radula

15
Mollusc Figure

• Is this a marine or land snail?

16
For More Info

• Australian Museum
• Their own scientific journal!

17
Phylum Annelida

• The segmented worms have many repeating body
  segments
• 3 groups
• Earthworms
• Polychaetes (Greek many hairs)
• Leeches

18
Complexity of Phyla is Increasing

• Porifera
• Cnidaria
• Platyhelminthes
• Nematoda
• Mollusca