Download ECOLOGY SPRING 2009 - Florida International University

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 protozoa
-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 in construction of the protostome lineage
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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
-Lophotrochozoa: mostly coelomates
-Include the phyla Brachiopoda,
Mollusca and Annelida
-Platyzoa: mostly acoelomates
-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: pseudocoelomates
-Roundworms
-Arthropoda: coelomates
-Insects, crustaceans, and others
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Parazoans lack tissues, organs and a definite
symmetry
-However, they have complex multicellularity
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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1. Inner layer = Specialized flagellate cells called
choanocytes, or collar cells
2. Central layer = Gelatinous, protein-rich matrix
called the mesohyl
3. Outer layer = Protective epithelium
Mesohyl may contain spicules and/or fibers of a
tough protein called spongin
-These strengthen the body of the sponge
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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)
-Forms the muscles
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Eumetazoans also evolved true body symmetry
-Radiata = Exhibit radial symmetry
-Phylum Cnidaria
-Phylum = Ctenophora
-Bilateria = Exhibit bilateral 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
The nematocyst is a special type of
cnidocyte, contains a small but powerful
harpoon, Used for food acquisition and
defense
Cnidarians have unique
specialized cells on their
epidermis called cnidocytes
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Hydrozoa (hydroids)
Scyphozoa (jellyfish)
Cubozoa (box jellyfish) Anthozoa (corals
and sea anemones)
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A small phylum whose members are
known as comb jellies, sea walnuts
or sea gooseberries
Structurally more complex
than cnidarians
Capture prey with a
colloblast
-Contains strong adhesive
material
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Ctenophores propel themselves through water with
eight rows of fused cilia
They are triploblastic
-Have true muscles cells derived from the mesoderm
Their mode of symmetry is not strictly radial as in
cnidarians
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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
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The flatworms are soft-bodied animals
-Many species are parasitic
-Others are free-living
Move by ciliated
epithelial cells
Have developed
musculature
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Flatworms lack a circulatory system
-Flattened body shape and highlybranched 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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Flatworms have been traditionally grouped into four
major classes
-Turbellaria
Free-living
-Monogenea
-Trematoda
-Cestoda
Parasitic
New studies group all three parasitic classes
into a single group, Neodermata
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Class Turbellaria
-Free-living flatworms
-Recently shown to be polyphyletic
-Found in freshwater, marine and even terrestrial
environments
Classes Monogenea and Trematoda
-Flukes
-Live as ectoparasites or endo-parasites in the bodies
of other animals
-Attach by suckers, anchors or hooks
-Most have a life cycle that involves two or more hosts
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Clonorchis sinensis: Oriental liver fluke
-Complex life cycle
-Miracidium – Ciliated stage in egg
-Rediae – Nonciliated larvae produced within
sporocyst
-Cercaria – Tadpole-like larval stage
-Metacercaria – Adult stage produced within
cysts
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Other important flukes are the blood flukes of the
genus Schistosoma
-Three species cause the disease
schistosomiasis, or bilharzia
-Worms coat themselves with host’s own antigens
-Thus, are immunologically invisible
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Class Cestoda
-Tapeworms
-Live as parasites within the bodies of other animals
-Most species occur
in the intestines of
vertebrates
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Acoel flatworms were once considered basal
members of the phylum Platyhelminthes
-Have a primitive nervous system and lack a digestive
cavity
Are now classified
in their own phyla,
Acoela
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Nemerteans are often called ribbon worms or
proboscis worms
Are long animals
that can stretch
to several meters
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Nematodes are roundworms comprising many
species
-Found in marine, freshwater and soil habitats
Are bilaterally symmetrical and unsegmented
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Possess a pseudocoel, which is a cavity between
the mesoderm and endoderm
-Serves as a hydrostatic skeleton, against which the
animal’s muscles can work
Pseudocoelomates lack a defined circulatory system
-Role is performed by fluids that move within the
pseudocoel
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Nematodes are roundworms comprising many
species
-Found in marine, freshwater and soil habitats
Are bilaterally symmetrical and unsegmented
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Nematodes are covered with a flexible, thick cuticle
Are ecdysozoans
-Molt cuticle four times
Lack specialized respiratory organs and exchange
oxygen through their cuticles
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Mouth is equipped with piercing organs called stylets
Food passes through the mouth by the sucking action
of the pharynx
Undigested material is eliminated through the anus
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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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