1. Question: Outline the structural features of Obelia (Cnidaria; hydrozoa) that characterize it as an animal showing an intermediate grade of organization

2. Definition of terms  Outline: provide a list.  Structural: physical form or make up.  intermediate: middle stage of animal development.  Provide a list of the physical form of Obelia that shows it is at the middle stage of animal development (transitional)

3. What does intermediate grade of organization mean??? The following can be used to define this term  Body plan  Symmetry  Tissues organization  Body cavity

4. Body plan  Animals vary tremendously in morphology, but their diversity is described by relatively few major body plans.  A body plan is a particular set of morphological and developmental traits.  Body plans provide a simple way to compare and contrast key animal features.

5. symmetry  A basic view when the animal is cut.  Symmetry may be radial or bilateral.  E.g. sponges lack symmetry, Cnidarians and Ctenophores have radial symmetry while Plathyhelminthes have bilateral symmetry.

6. Tissue organization  Primitive animals have cellular level of organization.  Diploblastic animals have a tissue level of organization.  Triploblastic animals show organ level of tissue organization.

7. Body cavity  Some animals lack a body cavity (aceolomate).  Some animals have body cavities completely lined by tissue derived from mesoderm (ceolomates).  Other animals have a body cavity that is not completely lined by tissue derived from mesoderm (pseudoceolomate).

8. General features of animals.  Multi-cellular, eukaryotic.  Heterotrophic; ingestion and detritivory.  No cell wall (but has intracellular junctions).  Nerve impulse conduction  Sexual reproduction.  Development; cleavage, gastrulation, metamorphosis (some species).

9. General characteristics of primitive animals that evolved before Obelia. (porifera)  They are just a loose aggregation of cells (no tissues/ organs/ organ systems).  No transport and nervous system. Individual cells react to environmental stimulus.  Most lack symmetry.  No body cavity hence no ceolome.

11. structural features of Obelia (Cnidaria; Hydrozoa)  Radial symmetry  Nerve net with some sensory tissues  Has a gastro-vascular cavity  No respiratory organs; water flows through colenteron as a mechanism of gaseous exchange  Poly morphic  Diploblastic

13. Now we come to………the general characteristic of more developed animals(bilateria)  Bilateral symmetry  Have a developed GV cavity  Exhibits cephalization  Have dorsal, ventral, anterior, posterial and ventral ends.  Triploblastic  Posses a blood vascular system  Specialized tissues  Undergo gastrulation  metamorphism

15. finally……the list of structural features that place obelia (Cnidaria; Hydrozoa) at the middle of animal development 1. Introduces symmetry(from no symmetry- radial symmetry-bilateral symmetry). 2. Introduces tissue level of organization.( from cellular level- diploblastic-triploblastic) 3. Adventism of a gv cavity. 4. Pioneers in terms of sensory tissue, possessing a nerve net (from no nerve-nerve net-cephalization). 5. 2 body plan (from one in porifera- two in Cnidaria- many in more developed animals).

18. CHAO……

19. GROUP MEMBERS  FELICITY DUBE R175385T  MARCHIA T. CHAGUMA R178458H  RICHARD DZIVA R175382E  TANAKA JAMINE CHAKANETSA R169932Y  TAFARA MUMBA R175393R  ROBERT ZIVENGWA  KUDAKWASHE MUDZAMIRI R1710911  CYNTHIA MUDZIMWA R1713207  KAHUNI KUNDAI R1710608  TRACY CHIPURIRO R178801D  KADZUNGWA LORRAINE T. R167146W  WASHARU JILL T. R176904J  DEVOTION TARIRAI R167124D