Question 17 Which major hypotheses describes the earliest ancestor of metazoan a

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Question 17 Which major hypotheses describes the earliest ancestor of metazoan as a bilateral organism and requires that cnidarians derive radial symmetry later? 1. Metazoa arose from a colonial flagellates form similar to Volvox which became independent and specialized. 2. Metazoans are derived from many separate lineages of unicellular organisms. 3. Metazoans arose from a multinucleate ciliate where cell boundaries eventually formed around each nucleus. 4. Eucoelomate bilateria evolved first then degenerated into single cells by schizogony 5. None of the choices are correct.

Explanation / Answer

Ans 3. Metazoans arose from a multinucleated ciliate where cell boundaries eventually formed around each nucleus.

This is Syncytial theory by Haji. The ancestral metazoan was at first Syncytial in structure and were bilaterally symmetrical. By cellularization it give rise to acoel(flatworm)

Acoel turbellaria is considered as primitive living metazoans.

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