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.
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 • Specialized digestive system, no anus
Flat worm parasitism &infestation • Complex lifecycles that involve parasitism and infestation of hosts. (see diagram for example)
Roundworms • 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
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 hermaphroditic.
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 • Digestive tract includes a gut • Has a nerve cord and nerve cells • 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.