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Biology 222Invertebrate Zoology II
Fall 2004Stephen M. Shuster
Northern Arizona University
Lecture 8
Bilateria, Revisited
Rotation at the Proto-Deutero Node
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BlastoporeFormation
a. This is an important part of earlier classification schemes
based on developmental characteristics.
b. Fate of blastopore differs among two major lines of
animals.1. Blastopore becomes mouth
- Protostomes2. Blastopore becomes anus -
Deuterostomes
Deuterostomes:
Lophophorates (?)
Chaetognatha
Echinodermata
Hemichordata
Chordata
Phylum Phoronida
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Phylum Brachiopoda
Phylum Ectoprocta (Bryozoa)
Phylum Chaetognatha1. Also known as “arrow worms” –small, highly voracious predators2. Will not be considered in great detail.
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Phylum Echinodermata
Hemichordates and Chordates
1. Highly specialized groups
with clear relationships to
each other
Hemichordates and Chordates
2. Synapomorphies:a. 22 – epithelia that binds to iodineb. 46 – pharyngeal gill slitsc. 52(4) – nervous system concentrated
dorsally
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Hemichordates and ChordatesClass EnteropneustaClass Pterobranchia
Subphylum UrochordataSubphylum
CephalochordataSubphylum Vertebrata
Hemichordates and ChordatesClass EnteropneustaClass Pterobranchia
Subphylum UrochordataSubphylum
CephalochordataSubphylum Vertebrata
Phylum Hemichordata1. Marine filter feeders2. Synapomorphiesa. 15 – preoral gut diverticulum that
supports anterior body - stomochordb. 51 –glomerulus as excretory organ.3. Classesa. Enteropneustab. Pterobranchia
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Phylum Hemichordata
Hemichordates and ChordatesClass EnteropneustaClass Pterobranchia
Subphylum UrochordataSubphylum
CephalochordataSubphylum Vertebrata
Phylum Chordata1. Ancestrally marine, sessile filter
feeders with motile larvae2. Synapomorphies:a. 39(1) – tripartite body cavity (again)b. 47 – notochordc. 48 – endostyle (becomes thyroid
gland in vertebrates)d. 63 – muscular, locomotory tail (in
larvae in urochordates)
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Phylum Chordata1. Representative Subphyla:
a. Urochordata – sea squirts and other ascidians
b. Cephalochordata - lanceletsc. Vertebrata – vertebrates
Hemichordates and ChordatesClass EnteropneustaClass Pterobranchia
Subphylum UrochordataSubphylum
CephalochordataSubphylum Vertebrata
Hemichordates and ChordatesClass EnteropneustaClass Pterobranchia
Subphylum UrochordataSubphylum
CephalochordataSubphylum Vertebrata
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Phylum Chordata1. Synapomorphies separating
Urochordates from Cephalochordates and Vertebrates:
a. 21 – myotomes – blocks of muscles arranges in segments.
b. 37 – longitudinal musculature derived from segmental enterocoelicpouching.
c. 94(6) – dorsal hollow nerve chord.
Subhylum Urochordata
Subphylum Cephalochordata
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νν
Subphylum VertebrataSubphylum Vertebrata
Protostomia
Protostomia1. Synapomorphiesa. 18(0) – Cleavage pattern spiral.b. 52(3) – Ventral or ventrolateral
synaptic nervous system.c. 74(1) – Entomesoderm derived from a
single mesentoblast (4d) cell.d. 75(1) – Subepidermal muscle in
sheets, derived (at least in part) from 4d cell.
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Protostomia1. Synapomorphies:a. 18(0) – Cleavage
pattern spiral.
CleavageCleavage1. After fertilization zygote must go from unicellular to
multicellular state.
2. Divisions are called cleavage because,
a. Cell size is reduced -reduction division.
b. No growth between cell divisions.
Blastomeresd. blastomeres vary in size
depending on type of cleavage and amount
of yolk present in ovum.
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BlastomeresBlastomeresvary in size
depending on type of
cleavage and amountof yolk
present in ovum.
Directions of Cleavage Planes and Blastomere
Fate
Two types of cleavage:
RadialSpiral
Directions of Cleavage Planes and Blastomere
Fate
Two types of cleavage:
RadialSpiral
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Directions of Cleavage planes and Blastomere
Fate
a. Radial Cleavage
1. Cell divisions occur along latitudinal or longitudinal
axes.
Radial Cleavage
3. Developmental fate of cells is indeterminate.
a. Cells can be separated and develop into
complete organisms.
b. Vertebrate zygotes are like this.
Spiral Cleavage1. Cell divisions are
longitudinal for first two divisions.
2. Then mitotic axes are transverse.
a. this causes blastomeres to appear to rotate.
b. usually dextropic; then levotropic; alternates to 64
cells.
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Spiral Cleavage
3. Developmental fate of cells is determinate.
4. After cleavage, you get a ball of cells.
Protostomia• Synapomorphies:• b. 52(3) – Ventral or
ventrolateral synaptic nervous system.
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Protostomia1. Synapomorphies:c. 74(1) – Entomesoderm derived from a single
mesentoblast (4d) cell.
Mesoderm and Coelom Formation
1. Mesoderm is derived from different sources in different
taxa.
2. An important aspect of development.
a. Third germ layer -represents an advance in structural organization.
MesodermSource of this layer is
associated with type and complexity of
coelom- the internal body cavity.
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Coelom
1. Involved in structural support.
2. Provides space for organs, movement,
gametes.c. Patterns of formation are
important in tracing phylogenies.
Sources of Mesoderm
3. In general, mesoderm sources
are:a. Protostomes: from
mesentoblast -endodermal cells near
anus.b. Deterostomes:
form enteric pouches.
Coelom FormationProtostomes
1. Mesoderm arises from vegetal cell (4d).
2. Arises near future anus.3. Forms two masses that later delaminate to form
coelom.a. Mesoderm spreads out to
form musculature and mesenteries.
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CoelomFormation
5. Mesodermal splitting to form coelom is called schizocoely.
Coelom FormationDeuterostomes
1. Mesoderm from enterocoelic pouches.2. Secondary schizocoely may occur.
3. Process proceeds the same as before.4. Mesodermal formation from pouches is enterocoely.
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Coelom Formation
Note: we now have some additional
characteristics that can be used
to classify Protostomes and Deuterostomes.
Protostomesa. Usually spiral,
determinate cleavage.b. Name from "first mouth"; blastopore
becomes mouth.c. Coelom formation by
schizocoely.d. Represent a major evolutionary lineage.
1. Some exceptions are now known; e.g. Lophophorates.
Deuterostomesa. Usually with radial, indeterminate cleavageb. Name from "second
mouth" blastoporebecomes anus, mouth
forms later.c. coelom formation by
enterocoelyd. also represent a major
evolutionary lineage1. again with some
exceptions.
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Protostomia1. Synapomorphies:75(1) – Subepidermal
muscle in sheets, derived (at least in part) from 4d cell.
Protostomia
Phylum Platyhelminthes
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Coelomate Protostomia
Coelomate Protostomia1. Synapomorphiesa. 77(1) – Schizocoelous coelom with body
cavity lined with mesodermally derived epithelium (peritoneum).
b. 95 – With trochophore larvae.
“Blastocoelomates”
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Blastocoelomates1. Gnathostomulida2. Entoprocta3. Cycliophora4. Rotifera5. Acanthocephala
6. Cycloneuraliaa. Gasterotrichab. Nematac. Nematomorphad. Priapulae. Kinorhynchaf. Loricifera
Phylum Nemertea
“Higher Protostomes”
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“Higher Protostomes”
SipunculaMolluscaEchiuraAnnelida
ArthropodaTardigrada
Onychophora