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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 Scientists generally agree about the taxonomic classification of 36 animal phylaof 36 animal phyla

-They do disagree, however, about how these are -They do disagree, however, about how these are interrelatedinterrelated

Traditional reconstructions lump together phyla that share Traditional reconstructions lump together phyla that share major features of body planmajor features of body plan

New reconstructions employ molecular comparisons of rRNA New reconstructions employ molecular comparisons of rRNA and other genesand other genes

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Both old and new phylogenies agree that: Both old and new phylogenies agree that: --PoriferaPorifera belongs to belongs to paraozoaparaozoa-Among the eumetazoans, -Among the eumetazoans, CnidariaCnidaria and and CtenophoraCtenophora branch branch out before out before BilateriaBilateria-Bilateria are divided into two groups: -Bilateria are divided into two groups: protostomesprotostomes and and deuterostomesdeuterostomes

Modern phylogeny differs radically from traditional phylogeny Modern phylogeny differs radically from traditional phylogeny in construction of the protostome lineagein construction of the protostome lineage

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Parazoans Parazoans lack tissues, organs and a definite symmetrylack tissues, organs and a definite symmetry

-However, they have complex multicellularity-However, they have complex multicellularity

Posess choanocytes, spongin, mesohyl, spicules, osculum. Posess choanocytes, spongin, mesohyl, spicules, osculum. Spicules found within the mesohyl.Spicules found within the mesohyl.

Sponges, phylum Sponges, phylum PoriferaPorifera, are parazoans, are parazoans

-Include marine and freshwater species-Include marine and freshwater species

-Larval sponges are free-swimming, but adults are anchored -Larval sponges are free-swimming, but adults are anchored onto submerged objects onto submerged objects

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Sponges use intracellular Sponges use intracellular

Digestion—Digestion—mostly bacteriamostly bacteria

Sponge reproductionSponge reproduction

-Asexual = Fragmentation-Asexual = Fragmentation

-Sexual = Egg and sperm-Sexual = Egg and sperm

-Larval sponges use cilia for swimming-Larval sponges use cilia for swimming

-Settle down on a substrate-Settle down on a substrate

-Transform into adults-Transform into adults

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EumetazoansEumetazoans are animals with distinct tissues are animals with distinct tissues

Embryos have distinct layersEmbryos have distinct layers

-Inner -Inner endodermendoderm = Forms the = Forms the gastrodermisgastrodermis

-Outer -Outer ectodermectoderm = Forms the = Forms the epidermisepidermis and nervous system and nervous system

-Middle -Middle mesodermmesoderm (Only in bilateral animals, (Only in bilateral animals, Ctnophora Ctnophora controversycontroversy))

-Forms the muscles-Forms the muscles

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Eumetazoans also evolved true body symmetryEumetazoans also evolved true body symmetry

--RadiataRadiata = Exhibit radial symmetry = Exhibit radial symmetry

-Phylum -Phylum CnidariaCnidaria

-Phylum = -Phylum = CtenophoraCtenophora

--Bilateria Bilateria = Exhibit radial symmetry= Exhibit radial symmetry

-All other animals-All other animals

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CnidariansCnidarians are carnivoresare carnivores

They have two basic body formsThey have two basic body forms• PolypsPolyps = Cylindrical and = Cylindrical and

sessilesessile• MedusaeMedusae = Umbrella-shaped = Umbrella-shaped

and free-livingand free-living

Gastrovascular cavity Gastrovascular cavity with with extracellular digestion. extracellular digestion. Derived from gastrodermisDerived from gastrodermis

Cnidarians have unique specialized cells on their epidermis called cnidocytes and nematocystsCnidarians can reproduce sexually creating a ciliated swimming larvae called a planulae.

Can be poly, medusa, or both in life cycle.

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HydrozoaHydrozoa (hydroids) (hydroids) Scyphozoa (jellyfish)

Cubozoa (box jellyfish) Anthozoa (corals & anemones)

ObeliaPolyp & Med.Hydra

JellyfishSex/asex

Has an endosymbiotic relationship with a dinoflagellate

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A small phylum whose members are known as comb jellies, sea A small phylum whose members are known as comb jellies, sea walnuts or sea gooseberrieswalnuts 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 The BilateriaBilateria are characterized by bilateral are characterized by bilateral symmetrysymmetry

• Allowed for high levels of specializationAllowed for high levels of specialization

Bilaterians are traditionally classified by the Bilaterians are traditionally classified by the condition of their coelomcondition of their coelom

• AcoelomatesAcoelomates• PseudoceolomatesPseudoceolomates• CoelomatesCoelomates

TriploblasticTriploblastic

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Modern protostome phylogeny distinguishes Modern protostome phylogeny distinguishes between two major clades that have evolved between two major clades that have evolved independently: independently:

--Spiralians: Spiralians: Grow by adding mass to an Grow by adding mass to an existing bodyexisting body

--Ecdysozoans: Ecdysozoans: Increase in size by molting their Increase in size by molting their external skeletonsexternal skeletons

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SpiraliansSpiralians• Grow by adding mass to an existing bodyGrow by adding mass to an existing body• Two main groupsTwo main groups

1.1. LophotrochozoaLophotrochozoa:: mostly coelomatesmostly coelomates• Include the phyla Brachiopoda, Mollusca and Annelida

2.2. PlatyzoaPlatyzoa:: mostly acoelomatesmostly acoelomates• Include the phyla Platyhelminthes, and Micrognathozoa

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EcdysozoansEcdysozoans• Increase in size by molting their external Increase in size by molting their external

skeletonsskeletons• Two phyla have been particularly successfulTwo phyla have been particularly successful

• Nematoda (roundworms): pseudocoelomates

• Arthropoda: coelomates• Insects, crustaceans, and others

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The flatworms are soft-bodied animalsThe flatworms are soft-bodied animals

Many species are parasiticMany species are parasitic

Others are free-livingOthers are free-living

TriploblasticTriploblastic

Flame cellsFlame cells

Move by ciliated epithelial cells

Have developed musculature

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Flatworms lack a Flatworms lack a circulatory system circulatory system -Flattened body shape -Flattened body shape and highly-branched gut and highly-branched gut utilize diffusionutilize diffusion

They have a simple They have a simple nervous systemnervous system--Eyespot Eyespot can distinguish can distinguish light from darklight from dark

Most are Most are hermaphroditichermaphroditic-Undergo sexual -Undergo sexual reproductionreproduction-Also have capacity for -Also have capacity for asexual regenerationasexual regeneration

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Three classes:Three classes:

1.1. TurbellariaTurbellaria: Free living flatworms. : Free living flatworms. Dugesia. Dugesia. 2.2. Monogenea and TematodaMonogenea and Tematoda: Flukes. : Flukes.

Endo and Ecto parasitesAdaptions of endoparasites—epidermis, sensory Simple and complex life cyclesImportant pathogens—liver flukes, blood flukes

3.3. CestodesCestodes: : TapewormsIntestinal parasiteNo digestive system.Scolex/neck/proglottids

4.4. All parasitic classes in NeodermataAll parasitic classes in Neodermata

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Nemerteans Nemerteans are often called ribbon worms or proboscis wormsare 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 Nematodes are roundworms comprising many species with are roundworms comprising many species with many sizes.many sizes.

Cuticle molts as it grows--EctysozoaCuticle molts as it grows--EctysozoaFound in marine, freshwater and soil habitatsFound in marine, freshwater and soil habitatsSome are parasites.Some are parasites.AreAre bilaterally symmetrical and unsegmentedbilaterally symmetrical and unsegmentedPharynxPharynxImportant human parasitesImportant human parasites

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Rotifers are bilaterally symmetrical unsegmented Rotifers are bilaterally symmetrical unsegmented pseudocoelomatespseudocoelomates

They have complex internal organsThey have complex internal organs

They propel themselves through water by rapidly beating thick cilia at They propel themselves through water by rapidly beating thick cilia at their headstheir heads-“Wheel animals”-“Wheel animals”

They gather food via a conspicuous organ called theThey gather food via a conspicuous organ called the coronacorona

Don’t forget quiz. Read chapters for next

week.