Transcript Noncoelomate Invertebrates Chapter 32 1

Noncoelomate Invertebrates
Chapter 32
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Invertebrate Phylogeny
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Two Approaches
– Traditional reconstructions are based on
key aspects of body architecture.
 lumping phyla that share fundamental
aspects of body plan
– New reconstructions employ molecular
comparisons.
 focus on differences in ribosomal RNA
sequences
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Traditional Protostome Phylogeny
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Novel rRNA Protostome Phylogenies
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Two major clades
– Lophotrochozoans
 flatworms
 mollusks
 annelids
– Ecdysozoans
 roundworms
 arthropods
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rRNA Protostome Phylogeny
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Parazoa
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Sponges (Porifera)
– most lack symmetry
– adults are sessile
– little coordination among cells
– three functional layers
 choanocytes
 mesohyl
 outer epithelial layer
 spicules
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Parazoa
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Beating of flagella lining interior draws water
in through numerous pores.
– Small organisms are filtered out of the
water, which flows through passageways
and eventually out an osculum.
Reproduction done by fragmentation as well
as sexually.
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Sponges
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Radiata
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Distinct tissues
– epidermis and nervous system develop
from ectoderm
– gastrodermis develops from endodermis
True body symmetry
– Radiata
 Cnidaria
 Ctenophora
– Bilateria
 all others
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Radiata
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Cnidarians
– nearly all marine
– carnivorous
 cnidocytes
 nematocysts
– two basic body plans
 polyps and medusae
– fertilized eggs give rise to planulae
– internal extracellular digestion
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Two Body Forms
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Cnidarians
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Radiata
Classes of Cnidarians
 Hydrozoa - hydroids
 Scyphozoa - jellyfish
 Cubozoa - box jellyfish
 Anthozoa - sea anemones and corals
Ctenophorans (comb jellies)
– propel through the water by means of
eight comb-like plates of fused cilia
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Bilateral Acoelomates
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Bilateral symmetry
– digestive tract is only internal cavity
Phylum Platyhelminthes: the flatworms
– Flatworms are among the simplest
bilaterally symmetrical animals, but they
have a definite head at the anterior end,
and do possess organs.
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The Bilateral Acoelomates
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Flatworms
– cannot feed, digest, and eliminate food
simultaneously
– absorb food directly through body walls
– have excretory system
 flame cells
– most are hermaphroditic
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Flatworm Architecture
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The Bilateral Acoelomates
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Class Turbellaria: turbellarians
 only one of three classes are freeliving
Class Trematoda: flukes
 life cycle liver fluke Clonorchis sinensis
 miracidium - eggs (passed in feces)
 rediae - elongated, nonciliated larvae
 cercariae - tadpole-like larval stage
 metacercariae - adult stage
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The Bilateral Acoelomates
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Class Cestoda: tapeworms
 hang on to inner walls of their hosts by
specialized terminal attachment organs,
and absorb food through their skins.
 scolex - attachment organ
 neck - unsegmented
 proglottids - repetitive segments
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The Bilateral Acoelomates
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Phylum Nemertea: ribbon worms
– simplest animals that possess a complete
digestive system
 mouth and anus
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The Pseudocoelomates
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Internal body cavity
– pseudocoel serves as hydrostatic skeleton
 gains rigidity from being filled with fluid
under pressure
– lack a defined circulatory system
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The Pseudocoelomates
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Phylum Nematoda: roundworms
– bilaterally symmetrical unsegmented worms
 covered by flexible, thick cuticle
– mouth equipped with stylets
– food passes through mouth as result of
sucking action of pharynx
– lack flagella or cilia
– reproduction is sexual
– Trichinella regularly parasitize humans
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Roundworms
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Nematode-Caused Diseases
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Trichinosis - Trichinella
Pinworms - Enterobius
Intestinal roundworms - Ascaris
Filariasis - Filaria
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The Pseudocoelomates
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Phylum Rotifera: rotifers
– small, bilaterally symmetrical, basically
aquatic animals with a crown of thick cilia at
their heads
– well developed food processing apparatus
– “wheel animals”
Phylum Cycliophora
– relatively new
 circular mouth surrounded by fine, hairlike
cilia
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