Practice question

Phoronids despite small vermiform dimensions possess surprisingly well-developed closed vascular system distinguishing them from many colonial bryozoans. System includes two major longitudinal vessels: dorsal median collecting and ventral median distributing, plus transverse connectives and dense capillaries in lophophore tentacles, body wall, intestine and nephridia, propelled by contractility of vessels themselves rather than discrete heart. Blood remains confined within vessels ensuring high pressure flow allowing efficient oxygen transport. Contains extracellular hemoglobin. Closed condition contrasts with open circulation of many ectoprocts, aligning phoronids more closely with brachiopods as advanced coelomate lophophorates adapted to low oxygen sediments and burrow life.