▁earlier ▁work ▁by ▁Per cy ▁Raymond , ▁thought ▁that ▁it ▁belonged ▁to ▁the ▁so - called ▁" tr il ob ito ids ". ▁After ▁his ▁thorough ▁analysis ▁Wh itt ington ▁concluded ▁that ▁Op ab in ia ▁was ▁no ▁ar th rop od , ▁as ▁he ▁found ▁no ▁evidence ▁for ▁ar th rop od an ▁joint ed ▁lim bs , ▁and ▁nothing ▁like ▁the ▁flexible , ▁probably ▁fluid - filled ▁prob os cis ▁was ▁known ▁in ▁ar th rop ods . ▁Although ▁he ▁left ▁Op ab ini as ▁classification ▁above ▁the ▁family ▁level ▁open , ▁the ▁ann ulated ▁but ▁not ▁art ic ulated ▁body ▁and ▁the ▁unusual ▁later al ▁lo bes ▁with ▁g ills ▁persu aded ▁him ▁that ▁it ▁may ▁have ▁been ▁a ▁representative ▁of ▁the ▁ancest ral ▁stock ▁from ▁which ▁both ▁the ▁ann el ids ▁and ▁ar th rop ods ▁arose . ▁ ▁In ▁ 1 9 8 5 , ▁D erek ▁Brig gs ▁and ▁Wh itt ington ▁published ▁a ▁description ▁of ▁An om al oc aris , ▁also ▁from ▁the ▁Burg ess ▁Sh ale . ▁Swedish ▁p ala e ont ologist ▁Jan ▁Berg ström ▁suggested ▁that ▁the ▁two ▁animals ▁were ▁related , ▁as ▁they ▁shared ▁later al ▁f laps ▁with ▁g ills , ▁st alk ed ▁eyes ▁and ▁other ▁features ; ▁and ▁he ▁class ified ▁them ▁as ▁primitive ▁ar th rop ods , ▁although ▁he ▁considered ▁that ▁ar th rop ods ▁are ▁not ▁a ▁single ▁ph yl um . ▁ ▁In ▁ 1 9 9 6 , ▁Graham ▁Bud d ▁found ▁what