Biology 222
Invertebrate Zoology II
Fall 2004
Stephen M. Shuster
Northern Arizona University
Lecture 5
The Principle of Parsimony
Occam’s Razor: That which can be
done in fewer steps is done in vain
with more.
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5 apomorphies
2 convergences
5 apomorphies
3 convergences
3 apomorphies
2 reversals
3 apomorphies
3 reversals
2
Metazoan
Phylogeny
Metazoan Phylogeny
c.f. Brusca and Brusca 2004
Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
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Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
Choanoflagellates
Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
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Porifera and Metazoa
a. Are distinct from choanoflagellates
by:
2. Multicellularity
4. Epithelial tight junctions
10. Collagen fibers in body
18(1). Development w/”radial” cleavage.
23. Spermatozoa
Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
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Porifera
a. Are distinct from the Placozoa by:
1. Collar cells (absent in Metazoa)
13. Striated ciliary rootlets (absent in Metazoa)
b. Also have the following apomorphies
1. Aquiferous system
2. Layered construction
3. Spicules
03.03B Barrel sponges
Glass sponge
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Pseudosuberites pseudos
Sponge Spicules
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Placozoa and other Metazoa
This clade includes all animals
(multicellular heterotrophs)
a. Synapomorphies:
1. Absence of collar cells
13. Striated ciliary rootlets
Tricoplax adhaerens
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Tricoplax adhaerens
Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
Cnidaria and Other
Metazoa
Includes the major animal phyla –
b. Synapomorphies
5. – Gap junctions
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Tight and Gap Junctions
Cnidaria and Other
Metazoa
Includes the major animal phyla –
b. Synapomorphies
5. – Gap junctions
11. – Organized gonads
31 – Ectoderm and endoderm (gastrulation)
52(1) – Nervous system with at least a nerve
net.
Cnidaria and Other
Metazoa
Other Characters:
65. – Basal lamina beneath epidermis
66. – Striated myofibrils
68.- Synaptic nervous system
69(1) – Primary symmetry – radial (as
ancestral trait)
93 – Body cuticle with collagen.
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Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
Hydra sp.
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Velella velella
Aurelia aurita
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Metridium senile
Lophogorgia chilensis
Sea fan and brain coral
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Lower Metazoan
Clades:
Choanoflagellata
Porifera
Placozoa
Cnidaria
Ctenophora
Ctenophora and Other Metazoa
Synapomorphies:
7. Acetylcholine
-cholinesterase
system at
synapses.
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Ctenophora
Autapomorphies:
1. comb rows
2. unique digestive
system
3. unusual symmetry
Bilateria
Bilateria
1. Includes two major groups separated
by particular developmental
characteristics:
a. Deuterostomia
b. Protostomia
2. We’ll get to these details shortly
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Bilaterian
Synapomorphies
Are mainly
associated with
body form and
nervous system
organization.
Synapomorphies Common
to Bilateria
a. 52(3) -Ventrally located nervous
system.
Ventrally Located Nervous
System
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Synapomorphies Common
to Bilateria
a. 52(3) -Ventrally located nervous
system.
b. 69(2) - Primary symmetry bilateral
with cephalization.
Primary Symmetry Bilateral
with Cephalization
Higher or Lower?
1. Some researchers consider the
Deuterostomes an ancestral group
relative to the rest of the animal taxa.
2. Others consider the Protostomes to
be more ancestral.
a. Note that it IS possible to rotate the
phylogeny around the DeuterostomeProtostome node.
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Rotation at the Proto-Deutero Node
Deuterostomia
1. Synapomorphies
a. 34(1) – mesoderm derived from
archenteron by enterocoelic pouching
b. 39 – tri partite coelom (anterior,
middle and posterior compartments)
c. 77(2) – internal body cavity lined by
peritoneum (mesodermally derived).
d. 86(0) – anterior body cavity
unmodified as a proboscis.
Deuterostomia
1. Synapomorphies:
a. 34(1) – mesoderm
derived from
archenteron by
enterocoelic
pouching
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Deuterostomia
1. Synapomorphies:
b. 39 – tri partite
coelom (anterior,
middle and
posterior
compartments)
Deuterostomia
1. Synapomorphies:
c. 77(2) – internal
body cavity lined
by peritoneum
(mesodermally
derived).
Deuterostomia
1. Synapomorphies:
86(0) – anterior body
cavity unmodified
as a proboscis,
trunk, collar (as in
hemichordates).
Phoronopsis californica
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Deuterostomes:
Lophophorates (?)
Chaetognatha
Echinodermata
Hemichordata
Chordata
Phylum Phoronida
Phylum Brachiopoda
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Phylum Ectoprocta (Bryozoa)
Phylum Chaetognatha
1. Also known
as “arrow
worms” –
small, highly
voracious
predators
2. Will not be
considered in
great detail.
Phylum Echinodermata
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