Body cavity As you develop, cells from a ball (blastula) that folds in on itself (gastrula). It makes 3 layers (germ layers): –Ectoderm (outside) becomes skin, etc. –Endoderm(inside) becomes organs and other tissues –Mesoderm (in between) becomes muscle

Body cavity What germ layers are where indicates type of body cavity –acoelemate has no body cavity. It is completely filled in (sponges, jellies, flatworms) –Pseudocoelemate appears to have a body cavity, but is not surrounded by muscles/tissues (round worms) –Coelemates have a true body cavity surrounded by muscle/other tissues (segmented worms, arthropods, mollusks, chordates, echinoderms)

Platyhelminthes Flat worms Bilateral symmetry Exchange O 2 /CO 2 through skin (diffusion) No circulatory system Incomplete digestive system (1 opening … gut) Cephalized (sensory organs at “head”) Pseudocoelemate…2 layers with fluid in between

Flat worms Many are parasites e.g. Planaria (Class Turbellaria) Scavenge for food, taken in through pharynx Water excreted through flame cells Cerebral ganglia collection of nerves (“brain”) Fission/sexual repro. (herm, exchange sperm) Eye spots sense light

Flat worms e.g. Flukes (Class Trematoda) Live blood, intestines, lungs, liver… Suckers to attach, draw in body fluids Hermaphroditic Life cycle with more than 1 host E.g. schistosomiasis

Schistosome Big one is female, little one is male Spread by snails! Causes enlargement of liver/spleen

Schistosomiasis

Flat worms e.g. tapeworms (class Cestaoda) live in intestines, absorb nutrients Scolex (head) has hooks and suckers to attach Produces eggs in proglottids (segments)

Tapeworm

Marine Flatworm

Nematoda Round worms Bilateral symmetry Pseudocoelemate…2 layers with fluid in between Complete digestive system (2 openings)…specialized organs with specific functions Seperate sexes Many are parasites

Roundworms Ascaris –Live in intestines  block them Hookworms –Live in intestinal wall, feed on blood  anemia Trichinella –Live in muscle  pain, stiffness, death Pinworms –Live in mesentaries of intestine, crawl out at night to lay eggs Filarial worms –Live in lymph system –Elephantiasis –Heartworms

Ascaris Worms

Hookworms

Heartworm

Trichinella

Pinworm G

Filarial worms

Filarial Worms

Elephantiasis Even once the worms are removed, it will stay like this the rest of their life Often infects genitalia/anal Often gets other infections that kill the person

Annelida “little rings”… segmented worms bilaterally symmetrical complete digestive tract true coelem … 2 layers, space between, allows body to expand/contract in parts segments allow worm to survive when some parts are damaged

Segmented worms Earthworms –Moves via setae, and 2 sets of muscles (circular and longitudinal) Squeeze circular muscle, and worm anterior moves forward, plants setae, squeeze longitudinal muscles to bring posterior up –Complete digestive system (mouth, pharynx, crop, gizzard, intestine, anus) –Closed circulatory system (blood moves posterior on dorsal side, anterior in ventral side)

Segmented worms –breathe through skin (why you see them on sidewalk when it rains) –ventral nerve cord and cerebral ganglia (“brain”) – nephridia (primitive kidney) in each segment –hermaphroditic, but exchange sperm to reproduce, then lay eggs – clitellum secretes mucus to hold them together

Earthworm

Leeches No setae…sucker at each end Secrete an anesthetic, so you don’t feel them, and a anticoagulent to keep blood from clotting Will fall off when “full,” otherwise pull them off (don’t cut or burn!) Used for reattachment surgery!

Class Hirudinea

OK…to end on a peaceful note, these, too, are segmented worms…. They’re marine worms called feather dusters…