30 2 INVERTEBRATE FLATWORMS OVERVIEW Phylum Platyhelminthes Sac

30. 2 INVERTEBRATE

FLATWORMS - OVERVIEW Phylum Platyhelminthes Sac body plan Bilateral symmetry Acoelomates: 3 germs layers but no coelom

More complex than earlier organisms � Muscles and excretory/reproductive/digestive systems � No respiratory or circulatory systems Thin, flat body � Allows diffusion to pass oxygen and other nutrients from cell to cell

FLATWORMS - PLANARIANS Habitat Freshwater (lakes, ponds, streams, and springs) Body Structure Small, flat worms Range of colour

Feeding and Digestion Feed on small living or dead organisms Wraps around prey and uses muscular pharynx to tear up food Pharynx leads to gastrovascular cavity Incomplete (only one opening)

Respiration, Circulation, and Excretion No circulatory or respiratory organs � Use diffusion to move dissolved oxygen and nutrients Excretory system made of network of interconnecting canals � Flame pores cell cilia move, moving water towards excretory

Response to Stimuli Regulated by nervous system � 2 nerve cords with connecting nerve tissue along body length � Ladder-like Small, anterior brain with 2 lateral nerve cords � Show cephalisation – have a brain, light-sensitive organs (eyespot), and chemosensitive organs around auricles Ganglion: group of nerve cell bodies that coordinates incoming/outgoing nerve signals

Movement 3 muscle layers (outer circular, inner longitudinal, an diagonal layer) allow for varied movement Glide along mucus film

Reproduction Are hermaphrodites(both male and female organs) Cross fertilization: penis of one is inserted into genital pore of another worm � Reciprocal transfer of sperm Can regenerate when cut in half

FLATWORMS – PARASITIC FLATWORMS

Flukes and tapeworms are 2 classes of parasitic flatworms. Both cause serious illness in humans Use secondary hosts as transport between primary hosts � Primary host infected with mature adult � Secondary host carries larval stage(s)

Habitat Depends on the species (can live in digestive tract, bile ducts, blood, and lungs) Ex. Schistosomes are blood flukes

Body Structure Hooks and suckers used to attach to host � Called the scolex in tapeworms Oval body shape Bilateral symmetry Anterior end has oral suckers with sensory papilla to attach to host

Feeding and Digestion Tapeworms essential have no digestive system � Use tegument – specialized body wall resistant to host’s digestive juices, covered with mucus coating

Reproduction Proglottids: contain muscles, nerves, flame cells, and reproductive organs � New ones form near scolex, pushing the older ones down � Mature proglottids basically sacs of eggs � Break off and are released in feces Larvae consumed by livestock and burrow into their bloodstream, encysting in the muscle � Cyst means to create a hard-walled structure that contains a larval worm Contaminated meat eaten by humans worms break cyst and thrive

ROUNDWORMS

Overview Phylum Nematoda Live anaerobically in animals and some plants 2 new features: Tube within a tube body plan and a body cavity

Habitat Diverse habitat – sea, fresh water, and soil

Body Structure Non-segmented (smooth outside body wall) Generally colourless and under 5 cm in length Tube within a tube body (mouth and anus)

Body cavity is pseudocoelom (incompletely lined with mesoderm) � Fluid-filled � Space for organ development Hydrostatic skeleton supports muscle contraction/flexibility

Feeding and Digestion Parasitic – obtain nutrients from host Respiration, Circulation, and Excretion No circulatory system � Pseudocoelom allows for easy passage of molecules

Reproduction Most have separate sexes Internal fertilization Eggs hatch into larvae that go through stages