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

Hookworms

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…