Coelomates. Echiura
The phylum Echiura (spoonworms) contains a small number
of marine worms with a circulatory system of similar
general pattern to that of the annelids. Main dorsal
and ventral vessels are united by contractile circumintestinal
vessels that pump the colourless blood. Coelomic fluid
probably aids in oxygen transport and may contain some
cells with hemoglobin.