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 recordHow 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 diversitywithout 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.

Phylum porifera; sponges. assymetrical

Because of assymetry, doesn’t fit into any neat story – so viewed as a development separate from everything else.

Symmetry, bilateral or radial

Jellyfish, corals, radial

cnideria

Radial symmetry plus one ended digestive system = primitive

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 =

Flatworms – one opening dig system, solid (acoelomate)

Round worms; two openings dig system pseudocoel

Seg. Worms (annelids) segments true coelom

Arthropods – trilobite = segmented and legs

Molluscs = chitin, segmented. Odd –legs??

Trilobite = arthropoda

Chitin = mollusca

Marine worm = annelida

All segmented.

Deuterostome, protostome split

Protostomes groups by segmentation.

Link segmentation together

Note: Classical classification((it’s wrong))

New phylogeny

• Lophotrochozoans

• Filter feeders

• Ecdysozoans

• 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.

Central position of flatworms as ancestral.

Question marks.

separate

Ecdysozoans

Shell shedders

segmented

NEXT

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.