PHYLUM PLATYHELMINTHES FLATWORMS

General Information 1.Usually flattened 2.No segments 3.Acoelomates 4.Bilateral symmetry 5.Cephalization- distinct head region w/brain-like organ. 6.Triploblastic- 3 tissue layers a. Ectoderm- make up the epidermis b. Endoderm- make up the digestive system. c. Mesoderm- make up all other organs

General Information 7. Three classes in Phylum Platyhelminthes – Class Turbellaria- free living flatworms (planarian & marine) – Class Trematoda- parasitic flukes – Class Cestoda- parasitic tapeworms

I. Class Turbellaria 1.Free-living planarians 2.Fresh or saltwater 3.Found crawling on stones, sand or vegetation 4.Have the ability to regenerate

Eyespot- senses light & dark Cerebral ganglion- simple brain Auricle- detects movement, chemicals, food Ventral Nerve Cord- transmits impulses thru body Anterior Intestine- transports nutrients to head end of planarian Pharyngeal Chamber- holds pharynx Pharynx- “sucks up” food like a straw Mouth- opening thru which pharynx extends Posterior Intestine- transports nutrients to tail end of planarian

Body Plan 1.Epidermis- outer layer of cells a. Ventral surface- belly 1. Cilia-movement 2. Genital pore- sexual reproduction 3. Mouth at end of pharynx- feeding b. Dorsal surface- back 1. Eyespots- sense light 2. Auricles- pointed sensory lobes at anterior end. Can detect: a. Chemicals b. Movement c. Food d. Water currents

2.Mesenchyme- layer of tissue that fills space around internal organs. a. Gland Cells- secrete mucous & adhesives thru skin. Aids in movement. b. Formative Cells- help regenerate damaged parts. 3.Muscle Layers- together create smooth swimming motion. a. Circular muscle- outer muscle extending around body. b. Longitudinal muscle- inner muscle runs the length of the worm.

Respiration: Flat bodies allow for simple diffusion

Digestion/Feeding 1. Can be carnivores, scavengers, or herbivores 2. Use extracellular digestion- digestion outside of body.

Dig. System 3.Pharynx extends from mouth and pharyngeal glands secrete enzymes that breakdown food into pieces. 4.Pharynx acts like a straw and “sucks” up the food pieces. 5.Food is passed into highly branched gastrovascular cavity w/ 3 extensions: 1.1 anterior intestinal branches 2.2 posterior intestinal branches 6.Whatever can’t be digested is ejected back out of the mouth. 7.Because GVC is so highly branched, there is no need for circulatory system to transport food.

Pharynx of planarian

Excretion- getting rid of excess liquid waste 1. Flame cells- contain cilia that create a current that collects extra water & liquid waste from tissues. 2. Excretory ducts- branching tubules that collect & transport water & wastes from flame cells. 3. Nephridiopore- holes in dorsal side that water & wastes are excreted through.

Nervous System 1. Looks like a ladder within body. 2. Double ventral nerve cord- picks up impulses from muscles & sends messages to cerebral ganglion. 3. Cerebral ganglion- simple brain; can detect light, movement, touch, water current & chemicals.

Reproduction 1. Asexual- transverse fission (regeneration) a. Head & tail separate into two immature planarians called zooids. b. Zooids eventually re-grow missing parts. Zooid

2. Sexual- monoecious/hermaphrodites a. Do not self-fertilize. b. Sperm made in several testis along lateral side c. Sperm pass along sperm ducts to seminal vesicle for storage. d. Planarians exchange sperm through the genital pore & store mates sperm in copulatory sac. e. Sperm migrate up oviduct to ovary to fertilize eggs. f. Fertilized eggs are enclosed in cocoon that contains yolk sac (provides food). g. Cocoon passed thru genital pore & will hatch within a few weeks.

Economic/Environmental Significance Planarians 1.Clean up water by eating detritus- dead, decaying matter. 2.Part of food chain. 3.Can be invasive species (Bipalium)

Bipalium- land planarians that eat earthworms found in: Powder Springs, Athens, Cornelia, Cumming, Dacula, Fayetteville, Marietta, Newnan, Peachtree City, Rome, Sharpsburg, and Stockbridge considered invasive species because eating so many earthworms will cause – Decrease in nutrients in soil – Increased flooding due to lack of aeration from earthworm burrows.