Where should the origin of the water vascular system be placed on the phylogenetic tree?

The answer is: at the base of Echinodermata. 

The water vascular system is used by Echinodermata for locomotion, respiration, and transportation of nutrients and waste. It consists of numerous tube feet connected by canals. Since it is present only in Echinodermata, on the phylogenetic tree, the origin of the water vascular system should be placed at the base of Echinodermata.

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