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Biology 222Invertebrate Zoology II

Fall 2004Stephen 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 apomorphies2 convergences

5 apomorphies3 convergences

3 apomorphies2 reversals

3 apomorphies3 reversals

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Metazoan Phylogeny

Metazoan Phylogenyc.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 Metazoaa. Are distinct from choanoflagellates

by:2. Multicellularity4. Epithelial tight junctions10. Collagen fibers in body18(1). Development w/”radial” cleavage.23. Spermatozoa

Lower Metazoan Clades:

Choanoflagellata

Porifera

Placozoa

Cnidaria

Ctenophora

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Poriferaa. 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 system2. Layered construction3. Spicules

03.03B Barrel sponges

Glass sponge

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Pseudosuberites pseudos

Sponge Spicules

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Placozoa and other MetazoaThis clade includes all animals

(multicellular heterotrophs)a. Synapomorphies:1. Absence of collar cells13. 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. Synapomorphies5. – Gap junctions

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Tight and Gap Junctions

Cnidaria and Other Metazoa

Includes the major animal phyla –

b. Synapomorphies5. – Gap junctions11. – Organized gonads31 – Ectoderm and endoderm (gastrulation)52(1) – Nervous system with at least a nerve

net.

Other Characters:

65. – Basal lamina beneath epidermis66. – Striated myofibrils68.- Synaptic nervous system69(1) – Primary symmetry – radial (as

ancestral trait)93 – Body cuticle with collagen.

Cnidaria and Other Metazoa

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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

Synapo-morphies:7. Acetylcholine -cholinesterase system at synapses.

Ctenophora and Other Metazoa

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Autapomorphies:

1. comb rows2. unique digestive system3. unusual symmetry

Ctenophora

Bilateria

Bilateria1. Includes two major groups separated

by particular developmental characteristics:a. Deuterostomiab. Protostomia

2. We’ll get to these details shortly

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BilaterianSynapomorphies

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 Deuterostome-Protostome node.

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Rotation at the Proto-Deutero Node

Deuterostomia1. Synapomorphiesa. 34(1) – mesoderm derived from

archenteron by enterocoelic pouchingb. 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.

Deuterostomia1. Synapomorphies:a. 34(1) – mesoderm

derived from archenteron by enterocoelicpouching

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Deuterostomia1. Synapomorphies:b. 39 – tri partite

coelom (anterior, middle and posterior compartments)

Deuterostomia1. Synapomorphies:c. 77(2) – internal

body cavity lined by peritoneum (mesodermallyderived).

Deuterostomia1. 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 Chaetognatha1. Also known as “arrow worms” –small, highly voracious predators2. Will not be considered in great detail.

Phylum Echinodermata