▁has ▁a ▁fairly ▁complicated ▁and ▁distinct ive ▁bur row ▁pattern : ▁along ▁a ▁central , ▁sometimes ▁sin uous ▁or ▁looping ▁bur row ▁it ▁made ▁success ive ▁prob es ▁up ward ▁through ▁the ▁sed iment ▁in ▁search ▁of ▁nut ri ents , ▁generating ▁a ▁trace ▁pattern ▁rem in is cent ▁of ▁a ▁fan ▁or ▁tw isted ▁ro pe . ▁The ▁organ ism ▁that ▁left ▁such ▁traces ▁is ▁considered ▁more ▁complex ▁than ▁earlier ▁Ed ia car an ▁fa una ; ▁and ▁these ▁trace ▁foss ils , ▁which ▁occur ▁world wide , ▁are ▁usually ▁found ▁in ▁str ata ▁above ▁those . ▁ ▁Since ▁only ▁its ▁bur rows ▁have ▁been ▁found , ▁it ▁is ▁pres umed ▁that ▁the ▁Tre pt ich n us ▁animal ▁lack ed ▁any ▁hard ▁an atom ical ▁features , ▁such ▁as ▁shell s ▁or ▁b ones . ▁ ▁Its ▁morph ology ▁and ▁relationship ▁to ▁modern ▁animals ▁is ▁therefore ▁unknown , ▁and ▁some ▁dispute ▁even ▁its ▁inclusion ▁within ▁the ▁animal ▁kingdom . ▁ ▁Despite ▁this ▁lack ▁of ▁foss il ▁evidence , ▁surface ▁tra ils ▁produced ▁by ▁modern ▁pri ap ul id ▁w orm s ▁exhib it ▁the ▁same ▁prob ing ▁morph ology ▁as ▁Tre pt ich n us , ▁suggesting ▁a ▁close ▁an atom ical ▁relationship ▁between ▁the ▁trace - maker ▁and ▁modern ▁pri ap ul ids . ▁ ▁The ▁name ▁Tre pt ich n us ▁ped um ▁means ▁" turn ed - tra il ▁( G reek ) ▁of ▁feet ▁( Lat in ) ". ▁ ▁References ▁ ▁Category : C amb rian