Noncoelomate Invertebrates

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Noncoelomate Invertebrates

• Chapter 33

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Invertebrate Phylogeny Revolution

• 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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Invertebrate Phylogeny Revolution

• Both old and new phylogenies agree that
• -Porifera first separated from Eumetazoa
• -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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Invertebrate Phylogeny Revolution

• Traditionally, the branches of animals are based
  on the nature of the body cavity
• -Acoelomates Have no body cavity
• -Pseudocoelomates Have pseudocoel
• -Coelomates Have coelom
• Acoelomates and pseudocoelomates are always
  protostomes
• Coelomates are either protostomes or deuterostomes

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Invertebrate Phylogeny Revolution
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Invertebrate Phylogeny Revolution

• Modern protostome phylogeny distinguishes between
  two major clades that have evolved independently
  
• -Spiralians
• -Ecdysozoans

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Invertebrate Phylogeny Revolution

• 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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Invertebrate Phylogeny Revolution

• 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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Invertebrate Phylogeny Revolution
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Parazoa

• 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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Parazoa

• Adult sponges are shaped like a vase

Walls of the vase have three functional layers
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Parazoa

• 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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Parazoa
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Parazoa

• Sponges are filter-feeders
• -Beating of the choanocyte flagella draws water
  through numerous small pores
• -Brings in food and oxygen and expels wastes
• -Small organisms are filtered from the water,
  which flows through passageways
• -Eventually exits from the osculum

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Parazoa

• 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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Eumetazoa

• 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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Eumetazoa

• 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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Phylum Cnidaria

• Cnidarians are nearly all marine
• -Bodies have distinct tissues but no organs
• Cnidarians are diploblastic
• -Ectoderm (epidermis) and endoderm
  (gastrodermis)
• -In between, a layer of gelatinous material
  (mesoglea)

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Phylum Cnidaria

• Cnidarians are carnivores
• They have two basic body forms
• -Polyps Cylindrical and sessile
• -Medusae Umbrella-shaped and free-living

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Phylum Cnidaria
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Phylum Cnidaria

• Some cnidarians exist as either medusae or
  polyps, while others alternate between the two
  phases
• Polyps may reproduce sexually or asexually
• -Asexual reproduction occurs by budding and may
  produce a new polyp or medusae
• Medusae reproduce sexually
• -Form free-swimming larvae called planulae

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Phylum Cnidaria

• Cnidarians have internal extracellular digestion
• -Digestion begins with extracellular
  fragmentation in the gastrovascular cavity
• -This is followed by phagocytosis and
  intracellular digestion
• Cnidarians have no circulatory, respiratory or
  excretory systems

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Phylum Cnidaria

• 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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Phylum Cnidaria
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Four Classes of Cnidarians

• Hydrozoa (hydroids)

Scyphozoa (jellyfish)
Cubozoa (box jellyfish)
Anthozoa (corals and sea anemones)
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Phylum Ctenophora

• 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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Phylum Ctenophora

• 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 Bilaterian Acoelomates

• 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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Phylum Platyhelminthes

• 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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Phylum Platyhelminthes

• Flatworms have an incomplete digestive cavity
  with only one opening
• -Therefore, they cannot feed continuously
• Muscular contractions in the pharynx allows food
  to be ingested and torn into small bits
• Tapeworms (parasitic flatworms) lack digestive
  systems
• -Absorb food directly through body walls

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Phylum Platyhelminthes

• Flatworms have an excretory and osmoregulatory
  system
• -Network of fine tubules runs through body
• -Flame cells located on the side branches
• -Primary function water balance
• -Secondary function excretion
• Metabolic wastes are excreted into the gut and
  eliminated through the mouth

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Phylum Platyhelminthes

• 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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Phylum Platyhelminthes
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Phylum Platyhelminthes
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Phylum Platyhelminthes

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

Free-living
New studies group all three parasitic classes
into a single group, Neodermata
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Phylum Platyhelminthes

• Class Turbellaria
• -Free-living flatworms
• -Recently shown to be polyphyletic
• -Found in freshwater, marine and even
  terrestrial environments

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Phylum Platyhelminthes

• 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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Phylum Platyhelminthes

• 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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Phylum Platyhelminthes

• Other important flukes are the blood flukes of
  the genus Schistosoma
• -Three species cause the disease
  schistosomiasis, or bilharzia
• -Worms coat themselves with hosts own antigens
• -Thus, are immunologically invisible

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Phylum Platyhelminthes

• Class Cestoda
• -Tapeworms
• -Live as parasites within the bodies of other
  animals

-Most species occur in the intestines of
vertebrates
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Phylum Platyhelminthes

• Class Cestoda
• -Long flat bodies divided into three zones
• -Scolex Attachment organ
• -Neck Unsegmented portion
• -Proglottids Repetitive sections
• -Each a complex hermaphroditic unit
• -Taenia saginata is the beef tapeworm

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Phylum Platyhelminthes
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Phylum Platyhelminthes

• 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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Phylum Nemertea

• Nemerteans are often called ribbon worms or
  proboscis worms

Are long animals that can stretch to several
meters
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Phylum Nemertea

• Nemerteans possess a fluid-filled sac, the
  rhynchocoel a true coelomic cavity
• Are the simplest animals with a complete
  digestive system (mouth and anus)
• Have a closed circulatory system
• They are not related to flatworms
• -Are now classified with other coelomate
  protostomes in the Lophotrochozoa

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Phylum Cycliophora

• Discovered in 1995
• Acoelomates that live on the mouthparts of claw
  lobsters
• Have unique anatomy and form of sexual
  reproduction

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The Pseudocoelomates

• Possess a pseudocoel, which is a cavity between
  the mesoderm and endoderm
• -Serves as a hydrostatic skeleton, against which
  the animals muscles can work
• Pseudocoelomates lack a defined circulatory
  system
• -Role is performed by fluids that move within
  the pseudocoel

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Phylum Nematoda

• Nematodes are roundworms comprising many species
• -Found in marine, freshwater and soil habitats
• Are bilaterally symmetrical and unsegmented

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Phylum Nematoda

• 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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Phylum Nematoda

• 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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Phylum Nematoda
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Phylum Nematoda

• Nematodes usually reproduce sexually
• -Sexes are separate
• Adults of some species exhibit eutely
• -Have a fixed number of cells
• -Caenorhabditis elegans has only 959 cells

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Phylum Nematoda

• Many nematodes are active hunters, preying on
  protists and other small animals
• Others are parasites of plants
• Still others live within the bodies of larger
  animals

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Phylum Nematoda

• Nematodes can cause diseases in humans

-Trichinella causes trichinosis -Forms cysts
in muscles
-Ascaris lumbricoides Intestinal roundworm
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Phylum Rotifera

• 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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Phylum Rotifera