Noncoelomate Invertebrates Chapter 32

Outline Invertebrate Phylogeny Parazoa Radiata The Bilaterian Acoelomates The Pseudocoelomates

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

Traditional Protostome Phylogeny

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

rRNA Protostome Phylogeny

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

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.

Sponges

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

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

Two Body Forms

Cnidarians

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

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.

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

Flatworm Architecture

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

Life Cycle of Human Liver Fluke

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

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

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

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

Roundworms

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

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

Summary Invertebrate Phylogeny Parazoa Radiata The Bilaterian Acoelomates The Pseudocoelomates