Worm Phylums

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

Flatworms Have bilateral symmetry Soft-bodied Invertebrates Common ex: –Tapeworms, flukes

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

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

Major Classes Evolutionary Milestone: Bilateral symmetry Cestoda Turbellaria Trematoda

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

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

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

Major Classes Evolutionary Milestones: Complete digestive tract, body cavity Adenophorea Secernentea

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

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)

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.

Major Classes Evolutionary Milestones: segmented body cavities Oligochaeta Polychaeta Hirudinea

Phylum & Class Exploration Each table has a worm representative from either Annelida, Platyhelminthes, or Nematoda. –In the next 20 minutes collect the following: 1 sample species, both common name and binomial nomenclature pictures of organisms in that class What makes that class different from other classes in the same phylum.