Phylum Nemertea (Rhynchocoela)
Phylum Nemertea (Rhynchocoela)
Phylum Nemertea (Rhynchocoela)
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Are <strong>Nemertea</strong>ns sister taxa with flatworms?<br />
First scenario<br />
• Origin of triploblasty, spiralian condition, a= Acoelomate ancestor (characters<br />
from ancestor a are retained in flatworms)<br />
3. Circulatory system, anus<br />
b = acoelomate ancestor<br />
4. <strong>Nemertea</strong>n synapomorphies (Characters from b are retained)<br />
5. Coelom<br />
Alternative scenario<br />
• Coelom. If 1 is coelom, flatworms lost the coelom (2)<br />
3. Coelom. If 3 is coelom, flatworms are primitively acoelomates and nemerteans<br />
either lost the coelom (4) or kept it in the form of rhynchocoel<br />
Coelomate ancestor b gives rise to coelomate phyla
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