Worms

1
Worms

• Read 524-529, 536-539
• HW 529 2-4
• 539 1-3

2
Types of worms

• There are 3 major phyla of worms
• Annelida segmented worms
• Platyhelminthes flat worms
• Nematoda round worms
• Interestingly, none of these worms are closely
  related to each other.

3
Flatworms

• Have bilateral symmetry
• Soft-bodied
• Invertebrates
• Common ex
• Tapeworms, flukes

4
Flatworm Anatomy

• No respiratory or circulatory organs and requires
  diffusion (resulting in the flat shape)
• Distinct brain
• Specialized digestive system, no anus

5
Flat worm reproduction

• Complex lifecycles that involve parasitism and
  infestation of hosts. (see diagram for example)

6
Major Classes

• Evolutionary Milestone Bilateral symmetry
• Cestoda- table 1
• Turbellaria- table 2
• Trematoda- table 3

7
Roundworms

• Un-segmented
• Bilateral
• Have adapted to every ecological niche
• Represent 90 of all life on the sea floor.
• Mostly microscopic
• Common examples
• Hookworm, C. elegans

8
Round worm anatomy

• Most are parasitic
• Contain a complete digestive system
• No respiratory or circulatory system
• Simple nervous system- main ventral nerve,
  smaller dorsal nerve cord
• Simple sensory organs at both ends

9
Reproduction

• Usually sexual.
• Males are smaller and have bent tails.
• Some are hemaphroditic.

10
Major Classes

• Evolutionary Milestones Complete digestive
  tract, body cavity
• Adenophorea
• Secernentea- table 4

11
Segmented worms

• Annelids are some of the most well-recognized
  worms.
• ex leeches and earthworms
• Found in most wet environments
• Range in size from one millimeter to over 3
  meters
• Hard chitin body

12
Anatomy of a segmented worm

• Major identifying characteristic is a segmented
  body.
• Invertebrates
• Bilateral symmetry
• Closed circulatory system
• Protostome with a coelom
• Digestive tract includes a gut
• Has a nerve cord and ganglia
• Contain photoreceptors (but not eyes)

13
Segmented worm reproduction

• Asexual reproduction still possible!
• Using fission, posterior part of worm breaks off
  to form a new clone worm.
• Considered the most highly organized animal to be
  able to perform complete regeneration
• Sexual reproduction can be hermaphroditic or have
  distinct sexes.
• Aquatic segmented worms perform external
  fertilization.
• Terrestrial worms are typically hermaphrodites
  and exchange gametes when laying next to each
  other.

14
Major Classes

• Evolutionary Milestones segmented body cavities
• Oligochaeta- table 5
• Polychaeta- table 6
• Hirudinea- table 7

15
Phylum Class Exploration

• Each table has been assigned a class from either
  annelida, platyhelminthes, or nematoda.
• In the next 20 minutes collect the following
• 1 sample species, both common name and binomial
  nomenclature
• 5 pictures of organisms in that class
• What makes that class different from other
  classes in the same phylum.