In this article we will discuss about the development characteristics of protostomes and deuterostomes. Protostomes: Developmental Characteristics: 1. Pattern of embryonic cleavage: Spiral cleavage pattern; the spiral cleavage is masked at the 6th cleavages (64-cell stage), e.g., Sipuncula, Echiura, Annelida, Pogonophora, Mollusca and some groups of Arthropoda (e.g., Myriapoda, Crustacea and Insecta except Chelicerata). 2. […]
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, […]
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 […]
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