Practice question
Question
Nemerteans differ from flatworms because they have
Explanation
Nemerteans superficially resemble turbellarian flatworms due to dorsoventrally flattened ciliated creeping body, soft unsegmented appearance, but fundamentally distinguished by several evolutionary advances: possession of true complete tubular system with separate anterior mouth and posterior anus allowing continuous unidirectional processing and fecal egestion, compared to incomplete blind branching gastrovascular cavity of Platyhelminthes, plus development of well-organized closed circulatory system with dorsal ventral vessels containing nucleated erythrocytes with hemoglobin absent in flatworms. Additionally possess protonephridial excretory system and unique rhynchocoel containing proboscis elevating them to higher grade approaching coelomates.
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