▁g astro zo oid . ▁The ▁g astro zo oid ▁has ▁a ▁tent acle ▁used ▁for ▁capt uring ▁and ▁dig est ing ▁food . ▁The ▁groups ▁also ▁have ▁g on op hor es , ▁which ▁are ▁special ized ▁for ▁reprodu ction . ▁They ▁use ▁a ▁p neum at oph ore , ▁a ▁gas - filled ▁float , ▁on ▁their ▁anterior ▁end ▁and ▁mainly ▁dr ift ▁at ▁the ▁surface ▁of ▁the ▁water . ▁Phys on ect s ▁have ▁a ▁p neum at oph ore ▁and ▁ne ct os ome , ▁which ▁har b ors ▁the ▁ne ct op hor es ▁used ▁for ▁jet ▁prop ulsion . ▁The ▁ne ct op hor es ▁p ump ▁the ▁water ▁back ▁in ▁order ▁to ▁move ▁forward . ▁Cal y cop hor ans ▁differ ▁from ▁c yst on ect s ▁and ▁phys on ect s ▁in ▁that ▁they ▁have ▁two ▁ne ct op hor es ▁and ▁no ▁p neum at oph ore . ▁ ▁Zo oid s ▁Si phon op hor es ▁can ▁have ▁zo oid s ▁that ▁are ▁either ▁poly ps ▁or ▁med us ae . ▁However , ▁zo oid s ▁are ▁unique ▁and ▁can ▁develop ▁to ▁have ▁different ▁functions . ▁N ect op hor es ▁N ect op hor es ▁are ▁med us ae ▁that ▁assist ▁in ▁the ▁prop ulsion ▁and ▁movement ▁of ▁some ▁si phon op hor es ▁in ▁water . ▁They ▁are ▁characteristic ▁in ▁phys on ect ae ▁and ▁cal y cop hor es . ▁The ▁ne ct op hor es ▁of ▁these ▁organ isms