The following points highlight the top six theories regarding the origin of metazoa. The theories are: 1. Syncytial-Ciliate Theory 2. Colonial Flagellate Theory 3. Colonial Blastea and Planula Theories 4. Gastraea Theory 5. Monophyletic Origin of Metazoans 6. Polyphyletic Origin of Metazoans. 1. Syncytial-Ciliate Theory: The origin of metazoans probably took place through the growth, nuclear division and cellularisation of [...]
In this article we will discuss about Echinoderms:- 1. Taxonomic Retrospect of Echinoderms 2. Definition and Origin of Echinoderms 3. Classification 4. Phylogenetic Considerations 5. Research 6. Habit and Habitat 7. Size 8. Shape and Symmetry 9. Body Wall and Skeleton 10. Digestive System 11. Coelom 12. Haemal System or Blood Lacunar System 13. Excretory System 14. Nervous System 15. [...]
In this article we will discuss about Phylum Chaetognatha:- 1. History of Phylum Chaetognatha 2. Features of Phylum Chaetognatha 3. Affinities. History of Phylum Chaetognatha: 1. Slabber, in the year 1769, was the first worker to record Sagitta and he placed it in the order Intestina under phylum Vermis. 2. Since then extensive works on various aspects of Sagitta have [...]