Animal diversity and relationships - Claremont Colleges

Animal diversity and relationships - Claremont Colleges

Animal diversity and relationships Living forms At least 30 phyla But only x important

ones Importance = numerous, ecologically important, and fit into

our conceptions of evolution Porifera = sponges

Assymetrical, 2 cell layers , internal silica spicules = skeleton. Cnideria, jellyfish, corals

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

Flatworms one opening dig system, solid (acoelomate) Trilobite = arthropoda Chitin = mollusca Marine worm = annelida

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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