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 O2/CO2 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
Marine Flatworm
Nematoda• Round worms• Bilateral symmetry• Pseudocoelemate…2 layers with
fluid in between• Complete digestive system (2
openings)…specialized organs with specific functions
• Separate 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
Heartworm
Trichinella
Pinworm
G
Pinworm
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…