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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 New reconstructions employ molecular comparisons of rRNA and other genescomparisons 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 cells2. Central layer = Gelatinous, protein-rich matrix called the mesohyl3. 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

Cnidarians have unique specialized cells on their epidermis called cnidocytes

The nematocyst is a special type of cnidocyte, contains a small but powerful harpoon, Used for food acquisition and defense

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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 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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Flatworms have been traditionally grouped into four major classes-Turbellaria-Monogenea -Trematoda-Cestoda

New studies group all three parasitic classes into a single group, Neodermata

Free-living

Parasitic

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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