Unsegmented worms

1. Phylum Platyhelminthes Otherwise known as FLATWORMS Characteristics: - bilateral symmetry - cephalization (development of nervous tissue at “head” end)

Free Living Flatworm (planaria)

Physiological Characteristics Feeding & Digestion Some are carnivores (suck food in at pharynx, branches into gastrovascular cavity Enzymes in cavity break down food which diffuses into body cells Some are parasites (feed on blood/tissue or host’s digested food) Circulation & Respiration Diffusion of O2 & CO2 across epidermal cells Flame cells help get rid of excess water Flame cells empty into tiny pores

More… Nervous System Free living worms have a “head” region & cephalization & primitive brain Long nerve cords (2) run down sides of body Ocelli sense light & dark Parasitic flatworms DO NOT have nervous tissue Locomotion (free living) Cilia in epidermal cells Muscle cells  allow for twisting & turning Reproduction Most are hermaphrodites (both male & female) Sexual: between 2 worms (egg fertilized by sperm) Asexual: binary fission

Class Turbellaria Example: Planarians, “cross eyed” freshwater worms Features: Flatworms; live in a variety of environments (land, fresh water, oceans)

Class Trematoda Example: Flukes (ex. Blood flukes) Features: Parasitic (internal or external); complex life cycle often involving several hosts Reproduce sexually or asexually Many are hermaphrodites

Class Cestoda Example: Tapeworm Features: Parasitic (most live in intestines of host) Scolex (head) contains suckers to embed in intestinal wall Absorbs nutrients from host

Fun with Flukes!

2. Phylum Nematoda Otherwise known as ROUNDWORMS Simple digestive system (mouth  intestines  anus) Range in size Most are free living; some parasitic

Physiological Characteristics Feeding & Digestion Long tube (mouth  anus) Many are carnivores, although some feed on decaying plant material Circulation & Respiration Diffusion; transfer of nutrients & gases internally also through diffusion

More… Nervous System GANGLIA in “head” region Long nerves run down length of body allow for movement Examples: hookworms, Ascaris (parasitic intestinal worm)