Lecture 8 - Northern Arizona University

Biology 222
Invertebrate Zoology II
Fall 2004
Stephen M. Shuster
Northern Arizona University
Lecture 8
Bilateria, Revisited
Rotation at the Proto-Deutero Node
1
Blastopore
Formation
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
- Protostomes
2. Blastopore becomes anus Deuterostomes
Deuterostomes:
Lophophorates (?)
Chaetognatha
Echinodermata
Hemichordata
Chordata
Phylum Phoronida
2
Phylum Brachiopoda
Phylum Ectoprocta (Bryozoa)
Phylum Chaetognatha
1. Also known
as “arrow
worms” –
small, highly
voracious
predators
2. Will not be
considered in
great detail.
3
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 iodine
b. 46 – pharyngeal gill slits
c. 52(4) – nervous system concentrated
dorsally
4
Hemichordates
and Chordates
Class Enteropneusta
Class Pterobranchia
Subphylum Urochordata
Subphylum
Cephalochordata
Subphylum Vertebrata
Hemichordates
and Chordates
Class Enteropneusta
Class Pterobranchia
Subphylum Urochordata
Subphylum
Cephalochordata
Subphylum Vertebrata
Phylum Hemichordata
1. Marine filter feeders
2. Synapomorphies
a. 15 – preoral gut diverticulum that
supports anterior body - stomochord
b. 51 –glomerulus as excretory organ.
3. Classes
a. Enteropneusta
b. Pterobranchia
5
Phylum Hemichordata
Hemichordates
and Chordates
Class Enteropneusta
Class Pterobranchia
Subphylum Urochordata
Subphylum
Cephalochordata
Subphylum Vertebrata
Phylum Chordata
1. Ancestrally marine, sessile filter
feeders with motile larvae
2. Synapomorphies:
a. 39(1) – tripartite body cavity (again)
b. 47 – notochord
c. 48 – endostyle (becomes thyroid
gland in vertebrates)
d. 63 – muscular, locomotory tail (in
larvae in urochordates)
6
Phylum Chordata
1. Representative Subphyla:
a. Urochordata – sea squirts and other
ascidians
b. Cephalochordata - lancelets
c. Vertebrata – vertebrates
Hemichordates
and Chordates
Class Enteropneusta
Class Pterobranchia
Subphylum Urochordata
Subphylum
Cephalochordata
Subphylum Vertebrata
Hemichordates
and Chordates
Class Enteropneusta
Class Pterobranchia
Subphylum Urochordata
Subphylum
Cephalochordata
Subphylum Vertebrata
7
Phylum Chordata
1. Synapomorphies separating
Urochordates from
Cephalochordates and Vertebrates:
a. 21 – myotomes – blocks of muscles
arranges in segments.
b. 37 – longitudinal musculature
derived from segmental enterocoelic
pouching.
c. 94(6) – dorsal hollow nerve chord.
Subhylum Urochordata
Subphylum Cephalochordata
8
Subphylum Vertebrata
ν
Protostomia
Protostomia
1. Synapomorphies
a. 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.
9
Protostomia
1. Synapomorphies:
a. 18(0) – Cleavage
pattern spiral.
Cleavage
1. 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.
Blastomeres
d. blastomeres vary in size
depending on type of
cleavage and amount
of yolk present in ovum.
10
Blastomeres
Blastomeres
vary in size
depending on
type of
cleavage and
amount
of yolk
present in
ovum.
Directions of
Cleavage Planes
and Blastomere
Fate
Two types of
cleavage:
Radial
Spiral
Directions of
Cleavage Planes
and Blastomere
Fate
Two types of
cleavage:
Radial
Spiral
11
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 Cleavage
1. 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.
13
Protostomia
1. 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.
Mesoderm
Source of this layer is
associated with type and
complexity of
coelom
- the internal body cavity.
14
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 Formation
Protostomes
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.
15
Coelom
Formation
5. Mesodermal splitting to form
coelom is called schizocoely.
Coelom Formation
Deuterostomes
1. Mesoderm from enterocoelic pouches.
2. Secondary schizocoely may occur.
3. Process proceeds the same as before.
4. Mesodermal formation from pouches is enterocoely.
16
Coelom Formation
Note: we now
have some
additional
characteristics
that can be used
to classify
Protostomes and
Deuterostomes.
Protostomes
a. 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.
Deuterostomes
a. Usually with radial,
indeterminate cleavage
b. Name from "second
mouth" blastopore
becomes anus, mouth
forms later.
c. coelom formation by
enterocoely
d. also represent a major
evolutionary lineage
1. again with some
exceptions.
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Protostomia
1. Synapomorphies:
75(1) – Subepidermal
muscle in sheets,
derived (at least in
part) from 4d cell.
Protostomia
Phylum
Platyhelminthes
18
Coelomate Protostomia
Coelomate Protostomia
1. Synapomorphies
a. 77(1) – Schizocoelous coelom with body
cavity lined with mesodermally derived
epithelium (peritoneum).
b. 95 – With trochophore larvae.
“Blastocoelomates”
19
Blastocoelomates
1.
2.
3.
4.
5.
Gnathostomulida
Entoprocta
Cycliophora
Rotifera
Acanthocephala
6. Cycloneuralia
a. Gasterotricha
b. Nemata
c. Nematomorpha
d. Priapula
e. Kinorhyncha
f. Loricifera
Phylum
Nemertea
“Higher Protostomes”
20
“Higher
Protostomes”
Sipuncula
Mollusca
Echiura
Annelida
Arthropoda
Tardigrada
Onychophora
21