Download ECOLOGY SPRING 2009 - Florida International University

The traditional metazoan phylogeny is being
reevaluated using molecular data. (Remember the
homology/analogy problem.)
Therefore, key morphological characters used in
traditional classification are not necessarily
conservative
Molecular systematics uses unique sequences within
certain genes to identify clusters of related groups
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Molecular data has helped to clarify the
relationship of different groups with the animals
(metazoans) for example annelids and
arthropods
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Most taxonomists agree that the metazoan
kingdom is monophyletic
Three prominent hypotheses have been proposed
for the origin of metazoans from single-celled
protists
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1. The multinucleate hypothesis
2. The colonial flagellate hypothesis
3. The polyphyletic origin hypothesis
Molecular systematics using rRNA sequences settles
this argument in favor of the colonial flagellate
hypothesis
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Scientists generally agree about the taxonomic classification
of 36 animal phyla
-They do disagree, however, about how these are
interrelated
Traditional reconstructions lump together phyla that share
major features of body plan
New reconstructions employ molecular comparisons of rRNA
and other genes
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Both old and new phylogenies agree that:
-Porifera belongs to paraozoa
-Among the eumetazoans, Cnidaria and Ctenophora branch
out before Bilateria
-Bilateria are divided into two groups: protostomes and
deuterostomes
Modern phylogeny differs radically from traditional phylogeny
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in construction of the protostome lineage
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Parazoans lack tissues, organs and a definite symmetry
-However, they have complex multicellularity
Posess choanocytes, spongin, mesohyl, spicules, osculum.
Spicules found within the mesohyl.
Sponges, phylum Porifera, are parazoans
-Include marine and freshwater species
-Larval sponges are free-swimming, but adults are anchored
onto submerged objects
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Sponges use intracellular
Digestion—mostly bacteria
Sponge reproduction
-Asexual = Fragmentation
-Sexual = Egg and sperm
-Larval sponges use cilia for swimming
-Settle down on a substrate
-Transform into adults
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Eumetazoans are animals with distinct tissues
Embryos have distinct layers
-Inner endoderm = Forms the gastrodermis
-Outer ectoderm = Forms the epidermis and nervous system
-Middle mesoderm (Only in bilateral animals, Ctnophora
controversy)
-Forms the muscles
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Eumetazoans also evolved true body symmetry
-Radiata = Exhibit radial symmetry
-Phylum Cnidaria
-Phylum = Ctenophora
-Bilateria = Exhibit radial symmetry
-All other animals
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Cnidarians are carnivores
They have two basic body forms
• Polyps = Cylindrical and
sessile
• Medusae = Umbrella-shaped
and free-living
Gastrovascular cavity with
extracellular digestion.
Derived from gastrodermis
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Cnidarians have unique specialized cells on their
epidermis called cnidocytes and nematocysts
Cnidarians can reproduce sexually creating a ciliated
swimming larvae called a planulae.
Can be poly, medusa, or both in life cycle.
Hydrozoa (hydroids)
Obelia
Polyp & Med.
Hydra
Scyphozoa (jellyfish)
Jellyfish
Sex/asex
Cubozoa (box jellyfish) Anthozoa (corals & anemones)
Has an
endosymbiotic
relationship
with a
dinoflagellate
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A small phylum whose members are known as comb jellies, sea
walnuts or sea gooseberries
• Structurally more complex than
cnidarians
• 8 rows cilia
• Capture prey with a colloblast
• Contains strong adhesive material
• Triploblastic (probably). Recent
molecular evidence has placed
ctenophors at the base of the
animal tree.
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The Bilateria are characterized by bilateral
symmetry
• Allowed for high levels of specialization
Bilaterians are traditionally classified by the
condition of their coelom
• Acoelomates
• Pseudoceolomates
• Coelomates
Triploblastic
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Modern protostome phylogeny distinguishes
between two major clades that have evolved
independently:
-Spiralians: Grow by adding mass to an
existing body
-Ecdysozoans: Increase in size by molting their
external skeletons
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Spiralians
•
Grow by adding mass to an existing body
Two main groups
1.
Lophotrochozoa: mostly coelomates
•
•
Include the phyla Brachiopoda, Mollusca and Annelida
Platyzoa: mostly acoelomates
2.
•
Include the phyla Platyhelminthes, and Micrognathozoa
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Ecdysozoans
• Increase in size by molting their external
skeletons
• Two phyla have been particularly successful
• Nematoda (roundworms): pseudocoelomates
• Arthropoda: coelomates
• Insects, crustaceans, and others
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The flatworms are soft-bodied animals
Many species are parasitic
Others are free-living
Triploblastic
Flame cells
Move by ciliated
epithelial cells
Have developed
musculature
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Flatworms lack a
circulatory system
-Flattened body shape
and highly-branched gut
utilize diffusion
They have a simple
nervous system
-Eyespot can distinguish
light from dark
Most are hermaphroditic
-Undergo sexual
reproduction
-Also have capacity for
asexual regeneration
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Three classes:
Turbellaria: Free living flatworms. Dugesia.
2. Monogenea and Tematoda: Flukes.
Endo and Ecto parasites
Adaptions of endoparasites—epidermis, sensory
Simple and complex life cycles
Important pathogens—liver flukes, blood flukes
3. Cestodes: Tapeworms
Intestinal parasite
No digestive system.
Scolex/neck/proglottids
4.
All parasitic classes in Neodermata
1.
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Nemerteans are often called ribbon worms or proboscis worms
• Are long animals
that can stretch
to several
meters.
• Rhynchocoel
• Complete
digestive system
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Nematodes are roundworms comprising many species with
many sizes.
Cuticle molts as it grows--Ectysozoa
Found in marine, freshwater and soil habitats
Some are parasites.
Are bilaterally symmetrical and unsegmented
Pharynx
Important human parasites
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Rotifers are bilaterally symmetrical unsegmented pseudocoelomates
They have complex internal organs
They propel themselves through water by rapidly beating thick cilia at
their heads
-“Wheel animals”
They gather food via a conspicuous organ called the corona
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