Radially symmetrical, 2 cell layers, one ended digestive system. Often with algae inside to provide nourishment Light sensitivity.
Ctenophora comb jellies Bilateral, one ended gut, marine Platyhelminthes = flat worms. Three cell
layers, no body cavity, one ended digestive system, brain, nerves, many are parasitic. Two ended digestive system Head and tail, have an internal
cavity not solid. Very numerous in soil. Annelida = segmented worms; bigger most free living. Have nerves, three cell layers, true body cavity = coelom, circulatory system, excretory system. Skin breathing and many have legs. Some carnivorous, soil eaters
or leaches blood suckers Mollusca: clams, snails, squid, octopus, slugs Two ended gut, nerves, circulation, filter feeders or carnivorous. Some (squid, octopus)
with eyes, brain, etc. Remnants of segmentation chitins. Arthropods joint leg = insects, crustacea Segmented, brain, sense organs, excretory
system Echinoderms pentaradiate, Starfish, urchins, sea lillys.
Chordata, including vertebrata . Backboned organisms. The fossil record How to determine relationships try fossils first.
Burgess Shale in British Columbia, a unique preservation at the right age. Segmented worms (with legs?)
arthropods Chordate similar to early members of this group
sponge ???? Result of fossil record: all major groups plus some other odd ones appear almost simultaneously = no sequental appearance.
How to make sense out of diversity without fossils. Rules: simple to complex symmetry (assymetrical, radial, bilateral)
Cell layers 1 to 2 to 3 Embryology - (old ontogeny recapitulates phylogeny statement of Haeckel) Digestive system design; one ended to two ended
Ernst Haeckel, 1866; ontogeny recapitulates phylogeny = early stages of development mirror
evolutionary changes. Note gill clefts in all embryos, tail present, etc.
Basis; development is often incremental add new stages to old harder to change the beginning stages.
Classic example of this, the aortic arches in vertebrates. Start with a complete set;
need gill arches to deposit them. All embryos have gill clefts and a complete set of arches To get to adult stages, loose
some of the arches. Because of assymetry, doesnt fit into any neat story so viewed as a development separate from everything
else. Phylum porifera; sponges. assymetrical
Symmetry, bilateral or radial Radial symmetry plus one ended digestive system =
primitive Jellyfish, corals, radial cnideria
Bilateral symmetry; all other groups. Clues from development 1. Hollow ball of cells 2. Then 2 cell layers, one
opening,radial symmetry= cnidaria 3. Then three cell layers new opening bilateral symmetry = all higher forms Cell layers 2 vs 3. sponges and cnideria = 2
Digestive system one ended vs. two ended Flatworms bilaterial but with one openning to digestive system
Other worms two ended digestive system. So: 1 no symmetry, followed by radial and then bilateral - porifera oldest then cnidaria, then everything else 2. one ended gut, followed by 2 ended.
3. 2 cell layers, followed by three Now what? Use embryology the great Protostome Deuterostome split
Protostomes vs deuterostomes
First opening = mouth Determinate clevage Spiral clevage
Mesoderm = 4d cell Schizocoel coelom
First opening = anus
Indeterminate clevage Radial clevage Mesoderm = infolding Endocoel coelom Protostomes how to organize
Classical method mesoderm solid to pseudocoelom to true coelom one ended gut to two ended no segments to segments
Body cavity (coelom) in relation to mesoderm Solid mesoderm = no coelom = flatworms acoelomate Coelom partially lined with mesoderm =
roundworms pseudocoele Coelom completely lines with mesoderm = Segmented worms, vertebrates, etc. true coelom
Result = Molluscs = chitin, segmented. Odd legs?? Arthropods trilobite = segmented and
legs Seg. Worms (annelids) segments true coelom Round worms; two openings dig system pseudocoel
All segmented. Deuterostome, protostome split Protostomes groups by
segmentation. Link segmentation together Note: Classical classification
((its wrong)) New phylogeny Lophotrochozoans
Ecdysozoans Filter feeders Shell shedders
Two phylogenies: left based on hypothesized relationships, right based on Both genetic similarity and time. Right is correct in that all major groups appear almost simultaneously (brushpile evolution)
Note: flatworms,mollusc and annelid together// no arthropods Arthropods and round worms in this group. N
E X T Ecdysozoans
Shell shedders separate Central position of flatworms as ancestral. Question marks.
segmented How come the old phylogeny wrong?
1. Segmentation arose more than once not a unifying trait 2. Some organisms, especially parasites (flatworms, roundworms) may have gotten simpler in structure through time. 3. A poor choice of unifying characters.
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