Transcript Parazoa-Eumetazoa dichotomy

Introduction to Animal Evolution
Define: animal
Unique characteristics:
Heterotrophic eukaryotes; ingestion
Lack cell walls; collagen
Nervous & muscular tissue
Sexual; diploid; cleavage; blastula; gastrulation;
larvae; metamorphosis
Regulatory genes: Hox genes
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Trend #1Multicellularity
Monophyletic Group
colonial flagellated protist
ancestor=choanoflagellates
Trend #1: Multicellularity
Hypothesis for the evolution of animals from
a colonial protist ancestor-
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Trend #2: Symmetry and Tissue
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Radial Symmetry:
• Cnidaria (hydra; ‘jellyfish’; sea
anemones)
• Ctenophora (comb jellies)~ radial
body symmetry
Trend #2: Symmetry and Tissue
Parazoa-Eumetazoa
dichotomy:
• sponges (Parazoa)~ no true
tissues
• all other animals
(Eumetazoa)~ true tissues
Diploblastic:
Triploblastic:
Endoderm
Endoderm
Ectoderm
Mesoderm
Ectoderm
Eumetazoa
Trend #3 Bilateral Symmetry, Internal
Organs, Cephalization
Trend #3 Bilateral Symmetry, Internal
Organs, Cephalization
• Bilateral Symmetry:
– DORSAL
– VENTRAL
– ANTERIOR
– POSTERIOR
•Internal Organs
•Cephalization
-Progressive increase in
nerve tissue at anterior
end as organisms
increase in complexity
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Trend #4: Body Cavity
Trend #4: Body Cavity
• Gastrovascular Cavities (GUTS)
are where food is digested, two
openings designate a digestive
tract
• A body cavity is a fluid filled
space separating the digestive
tract from the outer body wall
• Animals without a cavity
between the digestive tract and
the outer body wall are called
ACOELOMATES
Trend # 5: Coelom
•Embryonic development in
more advanced animals, a
cavity called a coelom
develops from tissue
developed from mesoderm
germ layer
•Cushions internal organs,
allows for expansion and
contraction
Trend # 5: Coelom
• Acoelomate, Pseudocoelomate, and
Coelomate Grades:
• triploblastic animals~ solid body, no body
cavity; called acoelomates (Platyhelminthesflatworms)
• body cavity, but not lined with mesoderm;
called pseudocoelomates (Rotifers,
Nematodes)
• true coelom (body cavity) lined with
mesoderm; called coelomate
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Trend # 6: Segmentation
• Insects and Certain worms= segmented
body parts
• Some body parts repeat, others are
adapted for specific functions
(Trend #7: Jointed Appendages
and Exoskeleton)
• Skeleton on the
outside, needs to
be shed to grow
• “Jointed foot”-legs,
antennae,
mouthparts
Trend #8 Deuterostome
Development
• During early development of zygote,
cell divisions, or cleavages occur
• Specific cleavage patterns occur
Protostome-Deuterostome dichotomy
among coelomates:
• protostomes (mollusks, annelids,
arthropods)
• 2 development patterns occur in two
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groups of animals:
deuterostomes (echinoderms,
chordates)
Trend #8 Deuterostome
Development
Protostome-Deuterostome dichotomy
among coelomates:
a) cleavage:
protostomes~ spiral and determinate
deuterotomes~ radial and
indeterminate
b) coelom formation:
protostomes~ schizocoelous;
deuterostomes~ enterocoelous
c) blastopore fate:
protostomes~ mouth from blastopore;
deuterostomes~ anus from blastopore
Trend # 9: Notochord
Trend # 9: Notochord