ding ▁process . ▁Zo oid s ▁are ▁the ▁mult ic ell ular ▁units ▁that ▁build ▁the ▁colon ies . ▁A ▁single ▁bud ▁called ▁the ▁pro - bud ▁initi ates ▁the ▁growth ▁of ▁a ▁col ony ▁by ▁under going ▁f ission . ▁Each ▁zo oid ▁is ▁produced ▁to ▁be ▁gen et ically ▁identical ; ▁however , ▁mut ations ▁can ▁alter ▁their ▁functions ▁and ▁increase ▁divers ity ▁of ▁the ▁zo oid s ▁within ▁the ▁col ony . ▁Si phon op hor es ▁are ▁unique ▁in ▁that ▁the ▁pro - bud ▁initi ates ▁the ▁production ▁of ▁diverse ▁zo oid s ▁with ▁specific ▁functions . ▁The ▁functions ▁and ▁organizations ▁of ▁the ▁zo oid s ▁in ▁colon ies ▁widely ▁vary ▁among ▁the ▁different ▁species ; ▁however , ▁the ▁majority ▁of ▁colon ies ▁are ▁bil ater ally ▁arranged ▁with ▁d ors al ▁and ▁vent ral ▁sides ▁to ▁the ▁stem . ▁The ▁stem ▁is ▁the ▁vertical ▁branch ▁in ▁the ▁center ▁of ▁the ▁col ony ▁to ▁which ▁the ▁zo oid s ▁attach .   Z o oid s ▁typically ▁have ▁special ▁functions , ▁and ▁thus ▁assume ▁specific ▁spatial ▁patterns ▁along ▁the ▁stem . ▁ ▁General ▁morph ology ▁ ▁Si phon op hor es ▁typically ▁exhib it ▁one ▁of ▁the ▁three ▁standard ▁body ▁plans . ▁The ▁body ▁plans ▁are ▁named ▁C yst on ect a , ▁Phys on ect a , ▁and ▁Cal y cop hor ae . ▁C yst on ect s ▁have ▁a ▁long ▁stem ▁with ▁the ▁attached ▁zo oid s . ▁Each ▁group ▁of ▁zo oid s ▁has ▁a