Invertebrates – Part 2 Worms and Mollusks

Worms

Characteristics soft-bodied, long, legless bilateral symmetry cephalization three cell layers epidermis gastroderm mesoderm

Phylum platyhelminthes

Phylum platyhelminthes The “flatworms” 3 Classes Turbellaria (free-living) Cestoda (tapeworms) Trematoda (flukes)

Class turbellaria

Planaria

Planaria

Life processes

MOVEMENT Ciliated cells Secrete a slime layer Muscles

NUTRITION Absorptive heterotroph Pharynx Intestine / Gastrovascular cavity Food: small animals and eggs

EXCRETION Flame cells Excretory pores

RESPONSE Anterior mass of nerve tissue (ganglia that act as a “brain”) Photoreceptors Longitudinal nerves Transverse nerves

REPRODUCTION Asexual – regeneration Sexual – hermaphroditic

Planarian Regeneration

Class cestoda

Parasitic Flatworms Few sense organs as adults No external cilia in adults Thick tegument Suckers and/or hooks

Taenia solium (the pork tapeworm)

Taenia solium Scolex Proglottid

Pork tapeworm lifecycle

Symptoms of Parasite Infection

Class trematoda

Opisthorchis sinensis (the Chinese liver fluke)

Chinese liver fluke lifecycle

Phylum nematoda