Phylum Platyhelminthes & Nematoda

Platyhelminthes Flatworms

3 Classes Turbellaria Trematoda Cestoda Free-living, most marine, flatworms Trematoda Parasitic, internal and external parasites, flukes Cestoda Parasitic, live in intestine of humans and other animals, long & ribbon-like, tapeworms

Characteristics Acoelomates – no true cavity Simplest animals with bilateral symmetry No specialized circulatory or respiratory system (uses diffusion to transport oxygen and nutrients) Excretes by diffusion

Characteristics Continue Cephalization (sense organs and nerve cells gathered into a head region) Primitive organ systems with true organs (digestion, excretion, reproduction) Sexual and asexual reproduction Hermaphroditic (both sexes) but do not self fertilize

Free-Living Flatworms (Aquatic) eg. Planaria

Planaria

Planaria – Class Turbellaria Both marine and freshwater Most are small (less then cm and few mm thick) Primitive nervous systems allows for coordination of body movements Simple eyes that detect light changes (responds to stimuli!)

Feeding Planaria have a gastrovacular cavity with 1 opening at end of muscular tube called a pharynx Pharynx is protrusible (can extend) Food is sucked into intestine via pharynx where enzymes digest food Nutrients diffuse to rest of cells in body Undigested material is ejested (spit out) via pharynx

Planarian Anatomy

Respiration Internal Transport Exchange of gases (oxygen/carbon dioxide) diffuse through body wall Internal Transport Gastrovascular cavity distributes products of digestion throughout body tissues via diffusion

Excretion Response Flame cells – expel water Metabolic waste removed by diffusion through body wall Response Most primitive animal with central nervous system (CNS) Sense organs Ocelli – eye spots sensitive to light Tactile and chemoreceptors on auricles (“ears”)

Movement Cilia on epidermal cells help it to glide through the water Mucus Does not swim freely = glides Muscles cells controlled by CNS Allows for reaction to environment Muscle fibers: longitudinally, circular and diagonally Allows the flatworm to twist and turn

Planaria Movement Video Clip

Reproduction Two types of reproduction Asexual reproduction Fission: constricting behind the pharynx and separates into 2 animals, each which regenerate the missing parts A planaria is cut in two and regenerates into 2 whole organisms Sexual reproduction Worms come together and join up, exchanging sperm & eggs Both sex organs on each worm (hermaphrodites) allow for cross fertilization of each worm

Planaria Regeneration Video

Flukes – Class Trematoda Parasitic Internal and External parasites Lifecycle usually involves 2 or more different host Animal intermediate host Human final (definitive) host Examples: Blood Fluke – Schistosoma mansoni Intermediate host is snails and definitive host is humans Liver Fluke Lung Fluke

Schistosoma mansoni Life cycle: Swimming larvae Burrow into snail Reproduce asexually Break out of snail Swim in water Bores through skin of human to blood vessels and then intestines Blood vessels leak eggs into intestines Very sick human

Tapeworms – Class Cestoda Found inside and outside hosts If inside cannot afford to grow too large or it will kill its host Some can reach up to 30 m in length (found in a sperm whale) Human tapeworms can be 7m Lack : sensory organs, coordination for mobility, digestive system Live in intestines - Feed on blood, tissue, fluids and pieces of cells

Tapeworms Continued Highly developed reproductive system capable of producing hundreds and thousands of egg and sperm. No digestive tract – absorb food as it passed by Attaches to host via suckers and hooks

Tapeworms Continued Have developed a way to maximize absorption of nutrients from their host by being flat and VERY long which increases their surface area to maximize the absorption of nutrients

Tapeworm Scolex

TAPEWORMS –Class Cestoda Scolex Proglottids (sections) form at anterior end

Tapeworm life cycle Mature proglottids break off posterior Eggs are released Animal eats contamination Forms a dormant cyst Human eats Hatch in host

Nematoda Roundworms

Key Characteristics Pseudocoelomate – fluid filled space between mesoderm and internal organs Bilateral symmetry Cephalization Most simplest animals to have mouth, anus and complete digestive tract 3 tissue layers: ectoderm, mesoderm & endoderm Body covered with a flexible nonliving cuticle secreted by ectoderm

Digestive System Tube shaped gut Food ingested, nutrients absorbed via diffusion, waste removed through anus Many are carnivorous, some are herbivores Some attach to the roots of plants and suck out the plant juices This can cause serious damage to plants and crops

Respiration Internal Transport Exchange of gases (oxygen/carbon dioxide) diffuse through body wall Internal Transport None

Excretion Nervous System Metabolic wastes (Carbon dioxide) leave by diffusion through body wall Nervous System Ganglia concentrated in head region – cephalization has a dorsal nerve cord and lateral nerve cord Nerves coordinate, transmit & control muscle movement and sensory input

Muscular System Reproduction Muscles run longitudinally Can bend either dorsally or ventrally Reproduction Most are either male or female Some are hermaphroditic

Parasitic Roundworms Complex lifecycles involving more than one host Whole lifecycle can occur in a single host Ex: Ascaris in human.

Trichonosis – 2 hosts