Question

I am a phylum of pseudocoelomate organisms. I have pulsatile blood vessels at first time.blood act as transport media first time in me.who am I?
Any give me the correct answer
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Answer 1

Answer:

Explanation:

A true coelom may be defined as a secondary body cavity, formed by the splitting of mesoderm during embryonic development and bounded on all sides by a definite coelomic epithelium or peritoneum. A true coelom probably appeared for the first time in annelids.