1. Noncoelomate Invertebrates
Chapter 32

2. Outline
Invertebrate Phylogeny
Parazoa
Radiata
The Bilaterian Acoelomates
The Pseudocoelomates

3. 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

4. Traditional Protostome Phylogeny

5. Novel rRNA Protostome Phylogenies
Two major clades
Lophotrochozoans
flatworms
mollusks
annelids
Ecdysozoans
roundworms
arthropods

6. rRNA Protostome Phylogeny

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

8. 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.

9. Sponges

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

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

12. Two Body Forms

13. Cnidarians

14. 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

15. 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.

16. 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

17. Flatworm Architecture

18. 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

19. Life Cycle of Human Liver Fluke

20. 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

21. The Bilateral Acoelomates
Phylum Nemertea: ribbon worms
simplest animals that possess a complete digestive system
mouth and anus

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

23. 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

24. Roundworms

25. Nematode-Caused Diseases
Trichinosis - Trichinella
Pinworms - Enterobius
Intestinal roundworms - Ascaris
Filariasis - Filaria

26. 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

27. Summary
Invertebrate Phylogeny
Parazoa
Radiata
The Bilaterian Acoelomates
The Pseudocoelomates