Noncoelomate Invertebrates

1
Noncoelomate Invertebrates

• Chapter 32

2
Invertebrate Phylogeny

• 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

3
Traditional Protostome Phylogeny
4
Novel rRNA Protostome Phylogenies

• Two major clades
• Lophotrochozoans
• flatworms
• mollusks
• annelids
• Ecdysozoans
• roundworms
• arthropods

5
rRNA Protostome Phylogeny
6
Parazoa

• Sponges (Porifera)
• most lack symmetry
• adults are sessile
• little coordination among cells
• three functional layers
• choanocytes
• mesohyl
• outer epithelial layer
• spicules

7
Parazoa

• 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.

8
Sponges
9
Radiata

• Distinct tissues
• epidermis and nervous system develop from
  ectoderm
• gastrodermis develops from endodermis
• True body symmetry
• Radiata
• Cnidaria
• Ctenophora
• Bilateria
• all others

10
Radiata

• Cnidarians
• nearly all marine
• carnivorous
• cnidocytes
• nematocysts
• two basic body plans
• polyps and medusae
• fertilized eggs give rise to planulae
• internal extracellular digestion

11
Two Body Forms
12
Cnidarians
13
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

14
Bilateral Acoelomates

• 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.

15
The Bilateral Acoelomates

• Flatworms
• cannot feed, digest, and eliminate food
  simultaneously
• absorb food directly through body walls
• have excretory system
• flame cells
• most are hermaphroditic

16
Flatworm Architecture
17
The Bilateral Acoelomates

• 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

18
The Bilateral Acoelomates

• 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

19
The Bilateral Acoelomates

• Phylum Nemertea ribbon worms
• simplest animals that possess a complete
  digestive system
• mouth and anus

20
The Pseudocoelomates

• Internal body cavity
• pseudocoel serves as hydrostatic skeleton
• gains rigidity from being filled with fluid under
  pressure
• lack a defined circulatory system

21
The Pseudocoelomates

• 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

22
Roundworms
23
Nematode-Caused Diseases

• Trichinosis - Trichinella
• Pinworms - Enterobius
• Intestinal roundworms - Ascaris
• Filariasis - Filaria

24
The Pseudocoelomates

• 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