How many lines of symmetry?

Fertilized egg

• Zygote is one diploid cell made by the fusion of the sperm and egg.

• In humans this is internal fertilization within the fallopian tubes.

• Many other organisms have external fertilization where the egg and sperm are both released outside the parent.

blastula

8 cell stage (blastocyst)morula

gastrula

Germ layers

• 3 kinds:– Ectoderm– Mesoderm– Endoderm

– Layers of cells that work together to form specific tissues.

– Sponges (0), cnidarian (2), others (all three)

Body plans: Coelom

If three germ layers, then….

PoriferaSponges

Sessile AdultsMotile Larvae

Assymetry

Very Primitive- “barely” multicellularClassified by hard skeletal spines called spicules

spicules

Investigating sponges

http://www.youtube.com/watch?v=BW05vMziy2o

Sponges spawning

http://www.youtube.com/watch?v=SHJOu9PjKyU

Body of sponge• Osculum: opening at the top• Ostia: openings in the wall of sponge

Cnidaria• Alternation of generations:

Most have both stages in life cycle

• Medusa: motile/sexual/tentacles down/mouth down

• Polyp: sessile/asexual/ mouth up/tentacles up

Characteristics of Cnidaria

• Nematocyst stingers Nerve net (no brain)

• Hydra• Hydra catching food: http://

www.youtube.com/watch?v=Kukv0AtIVdU&feature=related

• Hydra; http://www.youtube.com/watch?v=yqXkaZwiu6s&feature=related

• http://www.youtube.com/watch?v=v9j9iO6Zy4o&feature=PlayList&p=E9E1093124E2F9C9&playnext=1&index=3; jellyfish movement

• http://www.youtube.com/watch?v=M9MMp7QX6e0&feature=PlayList&p=E9E1093124E2F9C9&playnext=1&index=2 polyp stage

Cnidarians

• Portuguese Man-of-War are colonies of four kinds of highly modified polyps: feeding polyps, reproductive polyps, etc..

• Hydra• Hydra catching food:

http://www.youtube.com/watch?v=Kukv0AtIVdU&feature=related

Cnidaria: hydrozoa

Phylum Ctenophora: close relatives to cnidaria but jelly instead of

stingers• Comb jellies

http://www.youtube.com/watch?v=G7WT81ukHZE

Platyhelminthes FLATWORMS

• Tapeworms, Flukes (parasites), free swimming (planaria)

Cephalization

Notice the front end has sensory organs (HEAD?)

Most are parasitic and don’t have cephalization, but platyhelminthes were first to have it.

Characteristics

• Acoelomate/

• No coelom/organs

• Highly branched• Digestive system as

they have no circulatory system

Flatworm videos

• http://www.youtube.com/watch?v=voMKJea91gg free living flatworm

• http://www.youtube.com/watch?v=Ich4Y_K6GuM&feature=PlayList&p=E9E1093124E2F9C9&playnext=1&index=11 planaria eating

• http://www.youtube.com/watch?v=T6pAfQInf2c tapeworm in intestine

Fluke

• All parasitic• Most famous is the Sheep liver fluke that

causes schistosomiasis.• Over 100 million in the world have this

fluke/disease.