 Worm Anatomy:

 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.

 Have bilateral symmetry  Soft-bodied  Invertebrates  Common ex:  Tapeworms, flukes

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

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

 Un-segmented  Bilateral  Have adapted to every ecological niche  Represent 90% of all life on the sea floor.  Mostly microscopic  Can live in virtually any Moist environment  Have Digestive systems  Common examples:  Hookworm, Pinworms

 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

 Usually sexual.  Males are smaller and have bent tails.  Some are hermaphroditic.

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

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

 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.