ot rich s , ▁and ▁included ▁all ▁c ili ates ▁with ▁prominent ▁or al ▁c ilia : ▁heter ot rich s , ▁hyp ot rich s , ▁o lig ot rich s , ▁and ▁per it rich s , ▁although ▁the ▁last ▁were ▁soon ▁separated . ▁ ▁The ▁heter ot rich s ▁have ▁an ▁ad oral ▁zone ▁of ▁memb ran elles , ▁but ▁mole cular ▁and ▁ul tr astr ucture ▁studies ▁have ▁shown ▁they ▁are ▁a ▁separate ▁group ▁that ▁diver ged ▁from ▁most ▁other ▁c ili ates ▁early ▁on . ▁ ▁A ▁few ▁of ▁the ▁smaller ▁groups ▁included ▁with ▁them ▁may ▁be ▁genu ine ▁sp iro tr ich s , ▁however , ▁such ▁as ▁the ▁Pro to c ru zi ida . ▁ ▁The ▁remaining ▁sp iro tr ich s ▁form ▁a ▁mon oph y let ic ▁group , ▁but ▁their ▁relationships ▁are ▁uncertain . ▁ ▁For ▁the ▁most ▁part ▁the ▁o lig ot rich s ▁and ▁ch ore ot rich s ▁appear ▁to ▁form ▁closely ▁related , ▁natural ▁groups . ▁ ▁However ▁Hal ter ia ▁and ▁its ▁close ▁relatives , ▁originally ▁considered ▁o lig ot rich s , ▁form ▁a ▁separate ▁group ▁and ▁may ▁even ▁be ▁modified ▁st ich ot rich s . ▁ ▁Studies ▁also ▁suggest ▁the ▁hyp ot rich s ▁are ▁par ap hy let ic ▁to ▁the ▁st ich ot rich s , ▁and ▁possibly ▁to ▁the ▁o lig ot rich s ▁and ▁ch ore ot rich s ▁as ▁well . ▁ ▁This ▁stands ▁in ▁contrast ▁to ▁the ▁earlier