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